Document:

EX-10.5(b)

 Exhibit 10.5(b) 

SIENNA BIOPHARMACEUTICALS, INC. 

(F/K/A SIENNA LABS, INC.) 

2010 EQUITY INCENTIVE PLAN 

STOCK OPTION AGREEMENT 

Unless otherwise defined herein, the terms defined in the 2010 Equity Incentive Plan (the “Plan”) shall have the same defined
meanings in this Stock Option Agreement (the “Option Agreement”). 
  

	I.	NOTICE OF STOCK OPTION GRANT 

  

					
	Name:	 	  
	 	
			
	Address:	 	  
	 	
		 	  
	 	

 The undersigned Participant has been granted an Option to purchase Common Stock of Sienna Biopharmaceuticals,
Inc., a Delaware corporation (f/k/a Sienna Labs, Inc., the “Company”), subject to the terms and conditions of the Plan and this Option Agreement, as follows: 
  

					
	Date of Grant:	  	  
	 	
			
	Vesting Commencement Date:	  	  
	 	
			
	Exercise Price per Share:	  	  
	 	
			
	Total Number of Shares Granted:	  	  
	 	
			
	Total Exercise Price:	  	  
	 	
			
	Type of Option:	  	             Incentive Stock Option	 	
			
		  	             Nonstatutory Stock Option	 	
			
	Term/Expiration Date:	  	  
	 	

 Vesting Schedule: 

This Option shall be exercisable according to the following vesting schedule: 

 Termination Period: 

This Option shall be exercisable for three (3) months after Participant ceases to be a Service Provider, unless such termination is due
to Participant’s death or Disability, in which case this Option shall be exercisable for twelve (12) months after Participant ceases to be a Service Provider. Notwithstanding the foregoing sentence, in no event may this Option be exercised
after the Term/Expiration Date as provided above and this Option may be subject to earlier termination as provided in Section 13 of the Plan. 
  

	II.	AGREEMENT 

 1. Grant of Option. The Administrator of the Company hereby
grants to the Participant named in the Notice of Stock Option Grant in Part I of this Agreement (“Participant”), an option (the “Option”) to purchase the number of Shares set forth in the Notice of Stock Option Grant, at the
exercise price per Share set forth in the Notice of Stock Option Grant (the “Exercise Price”), and subject to the terms and conditions of the Plan, which is incorporated herein by reference. Subject to Section 18 of the Plan, in the
event of a conflict between the terms and conditions of the Plan and this Option Agreement, the terms and conditions of the Plan shall prevail. 

If designated in the Notice of Stock Option Grant as an Incentive Stock Option (“ISO”), this Option is intended to qualify as an
Incentive Stock Option as defined in Section 422 of the Code. Nevertheless, to the extent that it exceeds the $100,000 rule of Code Section 422(d), this Option shall be treated as a Nonstatutory Stock Option (“NSO”). Further, if
for any reason this Option (or portion thereof) shall not qualify as an ISO, then, to the extent of such nonqualification, such Option (or portion thereof) shall be regarded as a NSO granted under the Plan. In no event shall the Administrator, the
Company or any Parent or Subsidiary or any of their respective employees or directors have any liability to Participant (or any other person) due to the failure of the Option to qualify for any reason as an ISO. 

2. Exercise of Option. 

(a) Right to Exercise. This Option shall be exercisable during its term in accordance with the Vesting Schedule set out in the Notice
of Stock Option Grant and with the applicable provisions of the Plan and this Option Agreement. 
 (b) Method of Exercise. This
Option shall be exercisable by delivery of an exercise notice in the form attached as Exhibit A (the “Exercise Notice”) or in a manner and pursuant to such procedures as the Administrator may determine, which shall state the
election to exercise the Option, the number of Shares with respect to which the Option is being exercised (the “Exercised Shares”), and such other representations and agreements as may be required by the Company. The Exercise Notice shall
be accompanied by payment of the aggregate Exercise Price as to all Exercised Shares, together with any applicable tax withholding. This Option shall be deemed to be exercised upon receipt by the Company of such fully executed Exercise Notice
accompanied by the aggregate Exercise Price, together with any applicable tax withholding. 
 No Shares shall be issued pursuant to the
exercise of an Option unless such issuance and such exercise comply with Applicable Laws. Assuming such compliance, for income tax purposes the Shares shall be considered transferred to Participant on the date on which the Option is exercised with
respect to such Shares. 

  
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 3. Participant’s Representations. In the event the Shares have not been registered
under the Securities Act of 1933, as amended (the “Securities Act”), at the time this Option is exercised, Participant shall, if required by the Company, concurrently with the exercise of all or any portion of this Option, deliver to the
Company his or her Investment Representation Statement in the form attached hereto as Exhibit B. 
 4. Lock-Up Period.
Participant hereby agrees that Participant shall not offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer
or dispose of, directly or indirectly, any Common Stock (or other securities) of the Company or enter into any swap, hedging or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of any
Common Stock (or other securities) of the Company held by Participant (other than those included in the registration) for a period specified by the representative of the underwriters of Common Stock (or other securities) of the Company not to exceed
one hundred and eighty (180) days following the effective date of any registration statement of the Company filed under the Securities Act (or such other period as may be requested by the Company or the underwriters to accommodate regulatory
restrictions on (i) the publication or other distribution of research reports and (ii) analyst recommendations and opinions, including, but not limited to, the restrictions contained in NASD Rule 2711(f)(4) or NYSE
Rule 472(f)(4), or any successor provisions or amendments thereto). 
 Participant agrees to execute and deliver such other agreements
as may be reasonably requested by the Company or the underwriter which are consistent with the foregoing or which are necessary to give further effect thereto. In addition, if requested by the Company or the representative of the underwriters of
Common Stock (or other securities) of the Company, Participant shall provide, within ten (10) days of such request, such information as may be required by the Company or such representative in connection with the completion of any public
offering of the Company’s securities pursuant to a registration statement filed under the Securities Act. The obligations described in this Section 4 shall not apply to a registration relating solely to employee benefit plans on Form S-1
or Form S-8 or similar forms that may be promulgated in the future, or a registration relating solely to a Commission Rule 145 transaction on Form S-4 or similar forms that may be promulgated in the future. The Company may impose stop-transfer
instructions with respect to the shares of Common Stock (or other securities) subject to the foregoing restriction until the end of said one hundred and eighty (180) day (or other) period. Participant agrees that any transferee of the Option or
shares acquired pursuant to the Option shall be bound by this Section 4. 
 5. Method of Payment. Payment of the aggregate
Exercise Price shall be by any of the following, or a combination thereof, at the election of the Participant: 
 (a) cash; 

(b) check; 

  
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 (c) consideration received by the Company under a formal cashless exercise program adopted by the
Company in connection with the Plan; or 
 (d) surrender of other Shares which (i) shall be valued at its Fair Market Value on the date
of exercise, and (ii) must be owned free and clear of any liens, claims, encumbrances or security interests, if accepting such Shares, in the sole discretion of the Administrator, shall not result in any adverse accounting consequences to the
Company. 
 6. Restrictions on Exercise. This Option may not be exercised until such time as the Plan has been approved by the
stockholders of the Company, or if the issuance of such Shares upon such exercise or the method of payment of consideration for such shares would constitute a violation of any Applicable Law. 

7. Non-Transferability of Option. 

(a) This Option may not be transferred in any manner otherwise than by will or by the laws of descent or distribution and may be exercised
during the lifetime of Participant only by Participant. The terms of the Plan and this Option Agreement shall be binding upon the executors, administrators, heirs, successors and assigns of Participant. 

(b) Further, until the Company becomes subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act, or after the
Administrator determines that it is, will, or may no longer be relying upon the exemption from registration of Options under the Exchange Act as set forth in Rule 12h-1(f) promulgated under the Exchange Act (the “Reliance End Date”),
Participant shall not transfer this Option or, prior to exercise, the Shares subject to this Option, in any manner other than (i) to persons who are “family members” (as defined in Rule 701(c)(3) of the Securities Act) through gifts
or domestic relations orders, or (ii) to an executor or guardian of Participant upon the death or disability of Participant. Until the Reliance End Date, the Options and, prior to exercise, the Shares subject to this Option, may not be pledged,
hypothecated or otherwise transferred or disposed of, including by entering into any short position, any “put equivalent position” or any “call equivalent position” (as defined in Rule 16a-1(h) and Rule 16a-1(b) of the Exchange
Act, respectively), other than as permitted in clauses (i) and (ii) of this paragraph. 
 8. Term of Option. This Option
may be exercised only within the term set out in the Notice of Stock Option Grant, and may be exercised during such term only in accordance with the Plan and the terms of this Option Agreement. 

9. Tax Obligations. 
 (a)
Tax Withholding. Participant agrees to make appropriate arrangements with the Company (or the Parent or Subsidiary employing or retaining Participant) for the satisfaction of all Federal, state, local and foreign income and employment tax
withholding requirements applicable to the Option exercise. Participant acknowledges and agrees that the Company may refuse to honor the exercise and refuse to deliver the Shares if such withholding amounts are not delivered at the time of exercise.

 (b) Notice of Disqualifying Disposition of ISO Shares. If the Option granted to Participant herein is an ISO, and if Participant
sells or otherwise disposes of any of the Shares 

  
 -4- 

 
acquired pursuant to the ISO on or before the later of (i) the date two (2) years after the Date of Grant, or (ii) the date one (1) year after the date of exercise,
Participant shall immediately notify the Company in writing of such disposition. Participant agrees that Participant may be subject to income tax withholding by the Company on the compensation income recognized by Participant. 

(c) Code Section 409A. Under Code Section 409A, an Option that vests after December 31, 2004 (or that vested on or prior
to such date but which was materially modified after October 3, 2004) that was granted with a per Share exercise price that is determined by the Internal Revenue Service (the “IRS”) to be less than the Fair Market Value of a Share on
the date of grant (a “discount option”) may be considered “deferred compensation.” An Option that is a “discount option” may result in (i) income recognition by Participant prior to the exercise of the Option,
(ii) an additional twenty percent (20%) federal income tax, and (iii) potential penalty and interest charges. The “discount option” may also result in additional state income, penalty and interest tax to the Participant.
Participant acknowledges that the Company cannot and has not guaranteed that the IRS will agree that the per Share exercise price of this Option equals or exceeds the Fair Market Value of a Share on the date of grant in a later examination.
Participant agrees that if the IRS determines that the Option was granted with a per Share exercise price that was less than the Fair Market Value of a Share on the date of grant, Participant shall be solely responsible for Participant’s costs
related to such a determination. 
 10. Entire Agreement; Governing Law. The Plan is incorporated herein by reference. The Plan and
this Option Agreement constitute the entire agreement of the parties with respect to the subject matter hereof and supersede in their entirety all prior undertakings and agreements of the Company and Participant with respect to the subject matter
hereof, and may not be modified adversely to the Participant’s interest except by means of a writing signed by the Company and Participant. This Option Agreement is governed by the internal substantive laws of the State of California 

11. No Guarantee of Continued Service. PARTICIPANT ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES PURSUANT TO THE VESTING SCHEDULE
HEREOF IS EARNED ONLY BY CONTINUING AS A SERVICE PROVIDER AT THE WILL OF THE COMPANY (OR THE PARENT OR SUBSIDIARY EMPLOYING OR RETAINING PARTICIPANT) AND NOT THROUGH THE ACT OF BEING HIRED, BEING GRANTED THIS OPTION OR ACQUIRING SHARES HEREUNDER.
PARTICIPANT FURTHER ACKNOWLEDGES AND AGREES THAT THIS AGREEMENT, THE TRANSACTIONS CONTEMPLATED HEREUNDER AND THE VESTING SCHEDULE SET FORTH HEREIN DO NOT CONSTITUTE AN EXPRESS OR IMPLIED PROMISE OF CONTINUED ENGAGEMENT AS A SERVICE PROVIDER FOR THE
VESTING PERIOD, FOR ANY PERIOD, OR AT ALL, AND SHALL NOT INTERFERE IN ANY WAY WITH PARTICIPANT’S RIGHT OR THE RIGHT OF THE COMPANY (OR THE PARENT OR SUBSIDIARY EMPLOYING OR RETAINING PARTICIPANT) TO TERMINATE PARTICIPANT’S RELATIONSHIP AS
A SERVICE PROVIDER AT ANY TIME, WITH OR WITHOUT CAUSE. 

  
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 Participant acknowledges receipt of a copy of the Plan and represents that he or she is familiar
with the terms and provisions thereof, and hereby accepts this Option subject to all of the terms and provisions thereof. Participant has reviewed the Plan and this Option in their entirety, has had an opportunity to obtain the advice of counsel
prior to executing this Option and fully understands all provisions of the Option. Participant hereby agrees to accept as binding, conclusive and final all decisions or interpretations of the Administrator upon any questions arising under the Plan
or this Option. Participant further agrees to notify the Company upon any change in the residence address indicated below. 
  

					
	PARTICIPANT	 		 	SIENNA BIOPHARMACEUTICALS, INC.
			
	  
	 		 	  

	Signature	 		 	By
			
	  
	 		 	  

	Print Name	 		 	Print Name
			
	  
	 		 	  

		 		 	Title
			
	  
	 		 	
	Residence Address	 		 	

  
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 EXHIBIT A 

2010 EQUITY INCENTIVE PLAN 

EXERCISE NOTICE 
 Sienna
Biopharmaceuticals, Inc. 
 30699 Russell Ranch Road, Suite 140 

Westlake Village, CA 91362 
 Attention: President 

1. Exercise of Option. Effective as of today,
                    ,             , the undersigned
(“Participant”) hereby elects to exercise Participant’s option (the “Option”) to purchase
                         shares of the Common Stock (the “Shares”) of Sienna Biopharmaceuticals, Inc. (the
“Company”) under and pursuant to the 2010 Equity Incentive Plan (the “Plan”) and the Stock Option Agreement dated
                     (the “Option Agreement”). 

2. Delivery of Payment. Participant herewith delivers to the Company the full purchase price of the Shares, as set forth in the Option
Agreement, and any and all withholding taxes due in connection with the exercise of the Option. 
 3. Representations of Participant.
Participant acknowledges that Participant has received, read and understood the Plan and the Option Agreement and agrees to abide by and be bound by their terms and conditions. 

4. Rights as Stockholder. Until the issuance of the Shares (as evidenced by the appropriate entry on the books of the Company or of a
duly authorized transfer agent of the Company), no right to vote or receive dividends or any other rights as a stockholder shall exist with respect to the Common Stock subject to an Award, notwithstanding the exercise of the Option. The Shares shall
be issued to Participant as soon as practicable after the Option is exercised in accordance with the Option Agreement. No adjustment shall be made for a dividend or other right for which the record date is prior to the date of issuance except as
provided in Section 13 of the Plan. 
 5. Company’s Right of First Refusal. Before any Shares held by Participant or any
transferee (either being sometimes referred to herein as the “Holder”) may be sold or otherwise transferred (including transfer by gift or operation of law), the Company or its assignee(s) shall have a right of first refusal to purchase
the Shares on the terms and conditions set forth in this Section 5 (the “Right of First Refusal”). 
 (a) Notice of
Proposed Transfer. The Holder of the Shares shall deliver to the Company a written notice (the “Notice”) stating: (i) the Holder’s bona fide intention to sell or otherwise transfer such Shares; (ii) the name of each
proposed purchaser or other transferee (“Proposed Transferee”); (iii) the number of Shares to be transferred to each Proposed Transferee; and (iv) the bona fide cash price or other consideration for which the Holder proposes to
transfer the Shares (the “Offered Price”), and the Holder shall offer the Shares at the Offered Price to the Company or its assignee(s). 

 (b) Exercise of Right of First Refusal. At any time within thirty (30) days after
receipt of the Notice, the Company and/or its assignee(s) may, by giving written notice to the Holder, elect to purchase all, but not less than all, of the Shares proposed to be transferred to any one or more of the Proposed Transferees, at the
purchase price determined in accordance with subsection (c) below. 
 (c) Purchase Price. The purchase price (“Purchase
Price”) for the Shares purchased by the Company or its assignee(s) under this Section 5 shall be the Offered Price. If the Offered Price includes consideration other than cash, the cash equivalent value of the non-cash consideration shall
be determined by the Board of Directors of the Company in good faith. 
 (d) Payment. Payment of the Purchase Price shall be made, at
the option of the Company or its assignee(s), in cash (by check), by cancellation of all or a portion of any outstanding indebtedness of the Holder to the Company (or, in the case of repurchase by an assignee, to the assignee), or by any combination
thereof within thirty (30) days after receipt of the Notice or in the manner and at the times set forth in the Notice. 
 (e)
Holder’s Right to Transfer. If all of the Shares proposed in the Notice to be transferred to a given Proposed Transferee are not purchased by the Company and/or its assignee(s) as provided in this Section 5, then the Holder may sell
or otherwise transfer such Shares to that Proposed Transferee at the Offered Price or at a higher price, provided that such sale or other transfer is consummated within one hundred and twenty (120) days after the date of the Notice, that
any such sale or other transfer is effected in accordance with any applicable securities laws and that the Proposed Transferee agrees in writing that the provisions of this Section 5 shall continue to apply to the Shares in the hands of such
Proposed Transferee. If the Shares described in the Notice are not transferred to the Proposed Transferee within such period, a new Notice shall be given to the Company, and the Company and/or its assignees shall again be offered the Right of First
Refusal before any Shares held by the Holder may be sold or otherwise transferred. 
 (f) Exception for Certain Family Transfers.
Anything to the contrary contained in this Section 5 notwithstanding, the transfer of any or all of the Shares during the Participant’s lifetime or on the Participant’s death by will or intestacy to the Participant’s immediate
family or a trust for the benefit of the Participant’s immediate family shall be exempt from the provisions of this Section 5. “Immediate Family” as used herein shall mean spouse, lineal descendant or antecedent, father, mother,
brother or sister. In such case, the transferee or other recipient shall receive and hold the Shares so transferred subject to the provisions of this Section 5, and there shall be no further transfer of such Shares except in accordance with the
terms of this Section 5. 
 (g) Termination of Right of First Refusal. The Right of First Refusal shall terminate as to any
Shares upon the earlier of (i) the first sale of Common Stock of the Company to the general public, or (ii) a Change in Control in which the successor corporation has equity securities that are publicly traded. 

  
 -2- 

 6. Tax Consultation. Participant understands that Participant may suffer adverse tax
consequences as a result of Participant’s purchase or disposition of the Shares. Participant represents that Participant has consulted with any tax consultants Participant deems advisable in connection with the purchase or disposition of the
Shares and that Participant is not relying on the Company for any tax advice. 
 7. Restrictive Legends and Stop-Transfer Orders.

 (a) Legends. Participant understands and agrees that the Company shall cause the legends set forth below or legends substantially
equivalent thereto, to be placed upon any certificate(s) evidencing ownership of the Shares together with any other legends that may be required by the Company or by state or federal securities laws: 

THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 (THE “ACT”) AND MAY NOT BE OFFERED, SOLD
OR OTHERWISE TRANSFERRED, PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER THE ACT OR, IN THE OPINION OF COUNSEL SATISFACTORY TO THE ISSUER OF THESE SECURITIES, SUCH OFFER, SALE OR TRANSFER, PLEDGE OR HYPOTHECATION IS IN COMPLIANCE
THEREWITH. 
 THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN RESTRICTIONS ON TRANSFER AND A RIGHT OF FIRST REFUSAL HELD BY
THE ISSUER OR ITS ASSIGNEE(S) AS SET FORTH IN THE EXERCISE NOTICE BETWEEN THE ISSUER AND THE ORIGINAL HOLDER OF THESE SHARES, A COPY OF WHICH MAY BE OBTAINED AT THE PRINCIPAL OFFICE OF THE ISSUER. SUCH TRANSFER RESTRICTIONS AND RIGHT OF FIRST
REFUSAL ARE BINDING ON TRANSFEREES OF THESE SHARES. 
 THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO RESTRICTIONS ON TRANSFER FOR
A PERIOD OF TIME FOLLOWING THE EFFECTIVE DATE OF THE UNDERWRITTEN PUBLIC OFFERING OF THE COMPANY’S SECURITIES SET FORTH IN AN AGREEMENT BETWEEN THE ISSUER AND THE ORIGINAL HOLDER OF THESE SHARES AND MAY NOT BE SOLD OR OTHERWISE DISPOSED OF BY
THE HOLDER PRIOR TO THE EXPIRATION OF SUCH PERIOD WITHOUT THE CONSENT OF THE COMPANY OR THE MANAGING UNDERWRITER. 
 (b) Stop-Transfer
Notices. Participant agrees that, in order to ensure compliance with the restrictions referred to herein, the Company may issue appropriate “stop transfer” instructions to its transfer agent, if any, and that, if the Company transfers
its own securities, it may make appropriate notations to the same effect in its own records. 
 (c) Refusal to Transfer. The
Company shall not be required (i) to transfer on its books any Shares that have been sold or otherwise transferred in violation of any of the provisions of this Exercise Notice or (ii) to treat as owner of such Shares or to accord the
right to vote or pay dividends to any purchaser or other transferee to whom such Shares shall have been so transferred. 

  
 -3- 

 8. Successors and Assigns. The Company may assign any of its rights under this Exercise
Notice to single or multiple assignees, and this Exercise Notice shall inure to the benefit of the successors and assigns of the Company. Subject to the restrictions on transfer herein set forth, this Exercise Notice shall be binding upon
Participant and his or her heirs, executors, administrators, successors and assigns. 
 9. Interpretation. Any dispute regarding the
interpretation of this Exercise Notice shall be submitted by Participant or by the Company forthwith to the Administrator, which shall review such dispute at its next regular meeting. The resolution of such a dispute by the Administrator shall be
final and binding on all parties. 
 10. Governing Law; Severability. This Exercise Notice is governed by the internal substantive
laws, but not the choice of law rules, of the State of California. In the event that any provision hereof becomes or is declared by a court of competent jurisdiction to be illegal, unenforceable or void, this Exercise Notice shall continue in full
force and effect. 
 11. Entire Agreement. The Plan and Option Agreement are incorporated herein by reference. This Exercise Notice,
the Plan, the Option Agreement and the Investment Representation Statement constitute the entire agreement of the parties with respect to the subject matter hereof and supersede in their entirety all prior undertakings and agreements of the Company
and Participant with respect to the subject matter hereof, and may not be modified adversely to the Participant’s interest except by means of a writing signed by the Company and Participant. 

 

					
	Submitted by:	  		 	Accepted by:
			
	PARTICIPANT	  		 	SIENNA BIOPHARMACEUTICALS, INC.
			
	  
	  		 	  

	Signature	  		 	By
			
	  
	  		 	  

	Print Name	  		 	Print Name
			
		  		 	  

		  		 	Title
			
	Address:	  		 	
			
		  		 	Address:
			
	  
	  		 	
			
	  
	  		 	 30699 Russell Ranch Road, Suite 140
 Westlake
Village, CA 91362

			
		  		 	  

		  		 	Date Received

  
 -4- 

 EXHIBIT B 

INVESTMENT REPRESENTATION STATEMENT 
  

							
	PARTICIPANT	 	:	  	                                     
       	  	
				
	COMPANY	 	:	  	SIENNA BIOPHARMACEUTICALS, INC.	  	
				
	SECURITY	 	:	  	COMMON STOCK	  	
				
	AMOUNT	 	:	  	                     SHARES	  	
				
	DATE	 	:	  	                                     
               	  	

 In connection with the purchase of the above-listed Securities, the undersigned Participant represents to
Sienna Biopharmaceuticals, Inc., a Delaware corporation (f/k/a Sienna Labs, Inc., the “Company”), the following: 
 (a)
Participant is aware of the Company’s business affairs and financial condition and has acquired sufficient information about the Company to reach an informed and knowledgeable decision to acquire the Securities. Participant is acquiring these
Securities for investment for Participant’s own account only and not with a view to, or for resale in connection with, any “distribution” thereof within the meaning of the Securities Act of 1933, as amended (the “Securities
Act”). 
 (b) Participant acknowledges and understands that the Securities constitute “restricted securities” under the
Securities Act and have not been registered under the Securities Act in reliance upon a specific exemption therefrom, which exemption depends upon, among other things, the bona fide nature of Participant’s investment intent as expressed herein.
In this connection, Participant understands that, in the view of the Securities and Exchange Commission, the statutory basis for such exemption may be unavailable if Participant’s representation was predicated solely upon a present intention to
hold these Securities for the minimum capital gains period specified under tax statutes, for a deferred sale, for or until an increase or decrease in the market price of the Securities, or for a period of one (1) year or any other fixed period
in the future. Participant further understands that the Securities must be held indefinitely unless they are subsequently registered under the Securities Act or an exemption from such registration is available. Participant further acknowledges and
understands that the Company is under no obligation to register the Securities. Participant understands that the certificate evidencing the Securities shall be imprinted with any legend required under applicable state securities laws. 

(c) Participant is familiar with the provisions of Rule 701 and Rule 144, each promulgated under the Securities Act, which, in
substance, permit limited public resale of “restricted securities” acquired, directly or indirectly from the issuer thereof, in a non-public offering subject to the satisfaction of certain conditions. Rule 701 provides that if the
issuer qualifies under Rule 701 at the time of the grant of the Option to Participant, the exercise shall be exempt from registration under the Securities Act. In the event the Company becomes subject to the reporting requirements of

 
Section 13 or 15(d) of the Securities Exchange Act of 1934, ninety (90) days thereafter (or such longer period as any market stand-off agreement may require) the Securities exempt under
Rule 701 may be resold, subject to the satisfaction of the applicable conditions specified by Rule 144, including in the case of affiliates (1) the availability of certain public information about the Company, (2) the amount of
Securities being sold during any three (3) month period not exceeding specified limitations, (3) the resale being made in an unsolicited “broker’s transaction,” transactions directly with a “market maker” or
“riskless principal transactions” (as those terms are defined under the Securities Exchange Act of 1934) and (4) the timely filing of a Form 144, if applicable. 

In the event that the Company does not qualify under Rule 701 at the time of grant of the Option, then the Securities may be resold in
certain limited circumstances subject to the provisions of Rule 144, which may require (i) the availability of current public information about the Company; (ii) the resale to occur more than a specified period after the purchase and
full payment (within the meaning of Rule 144) for the Securities; and (iii) in the case of the sale of Securities by an affiliate, the satisfaction of the conditions set forth in sections (2), (3) and (4) of the paragraph
immediately above. 
 (d) Participant further understands that in the event all of the applicable requirements of Rule 701 or 144 are
not satisfied, registration under the Securities Act, compliance with Regulation A, or some other registration exemption shall be required; and that, notwithstanding the fact that Rules 144 and 701 are not exclusive, the Staff of the Securities
and Exchange Commission has expressed its opinion that persons proposing to sell private placement securities other than in a registered offering and otherwise than pursuant to Rules 144 or 701 shall have a substantial burden of proof in
establishing that an exemption from registration is available for such offers or sales, and that such persons and their respective brokers who participate in such transactions do so at their own risk. Participant understands that no assurances can
be given that any such other registration exemption shall be available in such event. 
  

	
	PARTICIPANT
	
	  

	Signature
	
	  

	Print Name
	
	  

	Date

  
 -2-EX-10.5(c)

 Exhibit 10.5(c) 

SIENNA BIOPHARMACEUTICALS, INC. 

(F/K/A SIENNA LABS, INC.) 

2010 EQUITY INCENTIVE PLAN 

STOCK PURCHASE RIGHT GRANT NOTICE AND RESTRICTED STOCK PURCHASE AGREEMENT 

Pursuant to its 2010 Equity Incentive Plan (the “Plan”), Sienna Biopharmaceuticals, Inc., a Delaware corporation (f/k/a
Sienna Labs, Inc., the “Company”), hereby grants to the Purchaser listed below (“Purchaser”), the right to purchase the number of shares of the Company’s Common Stock set forth below (the
“Shares”) at the purchase price set forth below (the “Stock Purchase Right”). This Stock Purchase Right is subject to all of the terms and conditions set forth herein, in the Plan and in the certain Restricted Stock
Purchase Agreement attached hereto as Exhibit A (the “Restricted Stock Purchase Agreement”), each of which is incorporated herein by reference. Unless otherwise defined herein, the terms defined in the Plan shall have the
same defined meanings in this Stock Purchase Right Grant Notice (the “Grant Notice”) and the Restricted Stock Purchase Agreement. 
  

					
	Purchaser:	 	  
	  	
			
	Date of Grant:	 	  
	  	
			
	Vesting Start Date:	 	  
	  	
			
	Purchase Price per Share:	 	  
	  	
			
	Number of Shares:	 	  
	  	
		
	Vesting Schedule:	 	 The Shares subject to this Stock Purchase Right shall vest and be released from the Company’s Repurchase Option, as set
forth in the Restricted Stock Purchase Agreement, according to the following schedule:
  

[25% of the Shares shall be released from the Company’s Repurchase Option (as defined in the Restricted Stock Purchase Agreement) on the first anniversary
of the Vesting Start Date and 1/48 of the Shares shall be released from the Repurchase Option on each monthly anniversary thereafter, so that 100% of the Shares shall be released from such Repurchase Option on the fourth (4th) anniversary of the Vesting Start Date, subject to Purchaser not experiencing a Termination of Service through each such vesting date.]

		
	Termination Date:	 	This Stock Purchase Right shall terminate if not exercised prior to the thirty-first (31st) day following the Date of Grant set forth above.

 By his or her signature and the Company’s signature below, Purchaser agrees to be bound by the terms and conditions of
the Plan, the Restricted Stock Purchase Agreement and this Grant Notice. Purchaser has reviewed the Restricted Stock Purchase Agreement, the Plan and this Grant Notice in their entirety, has had an opportunity to obtain the advice of counsel prior
to 

 
executing this Grant Notice and fully understands the provisions of this Grant Notice, the Restricted Stock Purchase Agreement and the Plan. Purchaser hereby agrees to accept as binding,
conclusive and final all decisions or interpretations of the Administrator of the Plan upon any questions arising under the Plan, this Grant Notice or the Restricted Stock Purchase Agreement. To the extent the Shares are issued in uncertificated
form, Purchaser also acknowledges and agrees that the Restricted Stock Purchase Agreement constitutes the notice required by Section 151(f) of the Delaware General Corporation Law. If Purchaser is married or in a registered domestic
partnership, his or her spouse or registered domestic partner has signed the Consent of Spouse or Domestic Partner attached to this Grant Notice as Exhibit D. 
  

													
	SIENNA BIOPHARMACEUTICALS, INC.:	 		 	PURCHASER:	 	
							
	By:	 		 	                                      
                                         
                	 		 	By:	 	  
	 	
	Print Name:	 		 	                                      
                                         
                	 		 	Print Name: 	 	  
	 	
	Title:	 		 	                                      
                                         
                	 		 	Title: 	 	  
	 	
	Address:	 		 	                                      
                                         
                	 		 	Address: 	 	  
	 	
		 		 	                                      
                                         
                	 		 		 	  
	 	

 Signature Page to Sienna Biopharmaceuticals, Inc. Stock Purchase Right Grant Notice 

 EXHIBIT A 

TO STOCK PURCHASE RIGHT GRANT NOTICE 

RESTRICTED STOCK PURCHASE AGREEMENT 

Pursuant to the Stock Purchase Right Grant Notice (the “Grant Notice”) to which this Restricted Stock Purchase Agreement
(this “Agreement”) is attached, Sienna Biopharmaceuticals, Inc., a Delaware corporation (f/k/a Sienna Labs, Inc., the “Company”), has granted to Purchaser (as defined in the Grant Notice) the right to purchase the
number of shares of Restricted Stock under the Company’s 2016 Equity Incentive Plan (the “Plan”) indicated in the Grant Notice. 

1. General. 
 1.1
Defined Terms. Capitalized terms not specifically defined herein shall have the meanings specified in the Plan and the Grant Notice. 

1.2 Incorporation of Terms of Plan. The Shares are subject to the terms and conditions of the Plan, which is incorporated herein by
reference. 
 2. Grant of Restricted Stock. 

2.1 Grant of Restricted Stock. In consideration of Purchaser’s agreement to remain in the employ of the Company or its
subsidiaries, if Purchaser is an Employee, or to continue to provide services to the Company or its subsidiaries, if Purchaser is a Consultant, or to serve as a Director, if Purchaser is a Director, and for other good and valuable consideration,
effective as of the Date of Grant set forth in the Grant Notice (the “Grant Date”), the Company irrevocably grants to Purchaser the right to purchase the Shares at any time prior to the Termination Date set forth in the Grant
Notice, upon the terms and conditions set forth in the Plan and this Agreement. 
 2.2 Purchase Price. The purchase price of the
Shares shall be as set forth in the Grant Notice, without commission or other charge (the “Purchase Price”). Unless otherwise determined by the Administrator and in accordance with the terms of the Plan, the Purchase Price shall be
paid by cash or check. 
 2.3 Issuance of Shares. The issuance of the Shares under this Agreement shall occur at the principal office
of the Company simultaneously with the execution of this Agreement by the parties or on such other date as the Company and Purchaser shall agree (the “Issuance Date”). Subject to the provisions of Section 3 below, on the
Issuance Date, the Company shall issue the Shares (which shall be issued in Purchaser’s name). 
 2.4 Conditions to Issuance of
Shares. The Shares, or any portion thereof, may be either previously authorized but unissued shares or issued shares which have then been reacquired by the Company. Such Shares shall be fully paid and nonassessable. The Company shall not be
required to issue or deliver any Shares prior to fulfillment of all of the following conditions: 

 (a) The admission of such Shares to listing on all stock exchanges on which the Company’s
Common Stock is then listed; and 
 (b) The completion of any registration or other qualification of such shares under any state or federal
law or under rulings or regulations of the Securities and Exchange Commission or of any other governmental regulatory body, which the Administrator shall, in its absolute discretion, deem necessary or advisable; and 

(c) The obtaining of any approval or other clearance from any state or federal governmental agency which the Administrator shall, in its
absolute discretion, determine to be necessary or advisable; and 
 (d) The receipt by the Company of full payment for such Shares,
including payment of all amounts which, under federal, state or local tax law, the Company (or other employer corporation) is required to withhold upon issuance of such Shares; and 

(e) The lapse of such reasonable period of time following the Issuance Date as the Administrator may from time to time establish for reasons
of administrative convenience. 
 2.5 Consideration to the Company. In consideration of the issuance of the Shares by the Company,
Purchaser agrees to render faithful and efficient services to the Company or any subsidiary. Nothing in the Plan or this Agreement shall confer upon Purchaser any right to (a) continue in the employ of the Company or any subsidiary or shall
interfere with or restrict in any way the rights of the Company and its subsidiaries, which are hereby expressly reserved, to discharge Purchaser, if Purchaser is an Employee, or (b) continue to provide services to the Company or any subsidiary
or shall interfere with or restrict in any way the rights of the Company or its subsidiaries, which are hereby expressly reserved, to terminate the services of Purchaser, if Purchaser is a Consultant, at any time for any reason whatsoever, with or
without cause, except to the extent expressly provided otherwise in a written agreement between the Company and Purchaser. 
 3.
Repurchase Option. 
 3.1 If Purchaser ceases to be a Service Provider for any reason, including for cause, death and Disability, the
Company or its assignee shall have the right and option to purchase from Purchaser, or Purchaser’s personal representative, as the case may be, all of Purchaser’s Unreleased Shares (as defined below) as of the date on which Purchaser
ceases to be a Service Provider at the purchase price paid by Purchaser for such Shares in connection with the Stock Purchase Rights (the “Repurchase Option”). 

3.2 The Company may exercise its Repurchase Option by delivering, personally or by registered mail, to Purchaser (or his or her transferee or
legal representative, as the case may be), within ninety (90) days of the date on which Purchaser ceases to be a Service Provider, a notice in writing indicating the Company’s intention to exercise the Repurchase

  
 2 

 
Option and setting forth a date for closing not later than thirty (30) days from the mailing of such notice. The closing shall take place at the Company’s office. At the closing, the
holder of any certificates for the Unreleased Shares being transferred shall deliver the stock certificate or certificates evidencing the Unreleased Shares, and the Company shall deliver the purchase price therefor. 

3.3 At its option, the Company may elect to make payment for the Unreleased Shares to a bank selected by the Company. The Company shall avail
itself of this option by a notice in writing to Purchaser stating the name and address of the bank, date of closing, and waiving the closing at the Company’s office. 

3.4 If the Company does not elect to exercise the Repurchase Option conferred above by giving the requisite notice within ninety
(90) days following the date on which Purchaser ceases to be a Service Provider, the Repurchase Option shall terminate. 
 3.5 One
hundred percent (100%) of the Shares shall initially be subject to the Repurchase Option. The Shares shall be released from the Repurchase Option in accordance with the Vesting Schedule set forth in the Grant Notice until all Shares are
released from the Repurchase Option. Fractional Shares shall be rounded to the nearest whole share. 
 3.6 Any Shares which from time to
time have not yet been released from the Company’s Repurchase Option pursuant to Section 3.5 above shall be referred to herein as “Unreleased Shares.” 

4. Transferability of the Shares; Escrow. 

4.1 Purchaser hereby authorizes and directs the Secretary of the Company, or such other person designated by the Company from time to time, to
transfer the Unreleased Shares as to which the Repurchase Option has been exercised from Purchaser to the Company. 
 4.2 To ensure the
availability for delivery of Purchaser’s Unreleased Shares upon repurchase by the Company pursuant to the Repurchase Option under Section 3 above, Purchaser hereby appoints the Secretary, or any other person designated by the Company from
time to time as escrow agent, as its attorney-in-fact to sell, assign and transfer unto the Company, such Unreleased Shares, if any, repurchased by the Company pursuant to the Repurchase Option and shall, upon execution of this Agreement, deliver
and deposit with the Secretary of the Company, or such other person designated by the Company from time to time, any share certificate(s) representing the Unreleased Shares, together with the stock assignment duly endorsed in blank, attached hereto
as Exhibit B. The Unreleased Shares and stock assignment shall be held by the Secretary, or such other person designated by the Company from time to time, in escrow, pursuant to the Joint Escrow Instructions of the Company and Purchaser
attached as Exhibit C hereto, until the Company exercises its Repurchase Option as provided in Section 3 above, until such Unreleased Shares are vested, or until such time as the Repurchase Option no longer is in effect. As a
further condition to the Company’s obligations under this Agreement, the spouse or registered domestic partner of Purchaser, if any, shall execute and deliver to the Company the Consent of Spouse or Domestic Partner attached hereto as
Exhibit D. Upon vesting of the Unreleased Shares, the escrow agent shall promptly deliver to Purchaser any 

  
 3 

 
certificate or certificates representing such Shares in the escrow agent’s possession belonging to Purchaser, and the escrow agent shall be discharged of all further obligations hereunder;
provided, however, that the escrow agent shall nevertheless retain such certificate or certificates, if any, as escrow agent if so required pursuant to other restrictions imposed pursuant to this Agreement. 

4.3 The Company, or its designee, shall not be liable for any act it may do or omit to do with respect to holding the Shares in escrow and
while acting in good faith and in the exercise of its judgment. 
 4.4 Transfer or sale of the Shares is subject to restrictions on transfer
imposed by Section 5 of this Agreement and any applicable state and federal securities laws. Any transferee shall hold such Shares subject to all of the provisions hereof and shall acknowledge the same by signing a copy of this Agreement. Any
transfer or attempted transfer of any of the Shares not in accordance with the terms of this Agreement shall be void and the Company may enforce the terms of this Agreement by stop transfer instructions or similar actions by the Company and its
agents or designees. 
 5. Purchaser’s Rights to Transfer Shares. 

5.1 Company’s Right of First Refusal. Before any Shares held by Purchaser or any permitted transferee (each, a
“Holder”) may be sold, pledged, assigned, hypothecated, transferred, or otherwise disposed of (each, a “Transfer”), the Company or its assignee(s) shall have a right of first refusal to purchase the Shares proposed
to be Transferred on the terms and conditions set forth in this Section 5 (the “Right of First Refusal”). In the event the Company’s charter, bylaws and/or a stockholders’ agreement applicable to the Shares contain a
right of first refusal with respect to the Shares, such right of first refusal shall apply to the Shares to the extent such provisions are more restrictive than the Right of First Refusal set forth in this Section 5 and the Right of First
Refusal set forth in this Section 5 shall not in any way restrict the operation of the Company’s charter, bylaws or the operation of any applicable stockholders’ agreement. 

(a) Notice of Proposed Transfer. In the event any Holder desires to Transfer any Shares, the Holder shall deliver to the Company a
written notice (the “Notice”) stating: (A) the Holder’s bona fide intention to sell or otherwise Transfer such Shares; (B) the name of each proposed purchaser or other transferee (“Proposed
Transferee”); (C) the number of Shares to be Transferred to each Proposed Transferee; and (D) the price for which the Holder proposes to Transfer the Shares (the “Offered Price”), and the Holder shall offer such
Shares at the Offered Price to the Company or its assignee(s). 
 (b) Exercise of Right of First Refusal. Within twenty-five
(25) days after receipt of the Notice, the Company and/or its assignee(s) may elect in writing to purchase all, but not less than all, of the Shares proposed to be Transferred to any one or more of the Proposed Transferees by delivery of a
written exercise notice to the Holder. The purchase price shall be determined in accordance with Section 5.1(c) hereof. 
 (c)
Purchase Price. The purchase price (“Repurchase Price”) for the Shares repurchased under this Section 5 shall be the Offered Price. Should the Offered Price 

  
 4 

 
specified in the Notice be payable in property other than cash, the Company or its assignee shall have the right to pay the purchase price in the form of cash equal in amount to the value of such
property, as determined by the Administrator. 
 (d) Payment. Payment of the Repurchase Price shall be made, at the option of the
Company or its assignee(s), in cash (by check or wire transfer), by cancellation of all or a portion of any outstanding indebtedness of the Holder to the Company (or, in the case of repurchase by an assignee, to the assignee), or by any combination
thereof within five (5) days after receipt of the Notice or in the manner and at the times mutually agreed to by the Company and the Holder. 

(e) Holder’s Right to Transfer. If all of the Shares proposed in the Notice to be Transferred are not purchased by the Company
and/or its assignee(s) as provided in this Section 5, then the Holder may sell or otherwise Transfer such Shares to that Proposed Transferee at the Offered Price or at a higher price, provided that such sale or other Transfer is consummated
within sixty (60) days after the date of the Notice and provided further that any such sale or other Transfer is effected in accordance with any Applicable Laws and the Proposed Transferee agrees in writing that the provisions of this
Section 5 and the Restricted Stock Purchase Agreement, if applicable, shall continue to apply to the Shares in the hands of such Proposed Transferee. If the Shares described in the Notice are not Transferred to the Proposed Transferee within
such 60-day period, a new Notice shall be given to the Company, and the Company and/or its assignees shall again be offered the Right of First Refusal as provided herein before any Shares held by the Holder may be sold or otherwise Transferred. 

5.2 Exception for Certain Family Transfers. Anything to the contrary contained in this Section 5 notwithstanding and to the extent
permitted by the Administrator, the Transfer of any or all of the Shares during Purchaser’s lifetime or upon Purchaser’s death by will or intestacy to Purchaser’s Immediate Family or a trust for the benefit of Purchaser’s
Immediate Family shall be exempt from the Right of First Refusal. As used herein, “Immediate Family” shall mean spouse, lineal descendant or antecedent, father, mother, brother or sister or stepchild (whether or not adopted). In
such case, the transferee or other recipient shall receive and hold the Shares so Transferred subject to the provisions of the Plan, this Agreement and any other applicable agreements, and there shall be no further Transfer of such Shares except in
accordance with the terms of this Section 5 (or otherwise as expressly provided under the Plan). 
 5.3 Termination of Right of
First Refusal. The Right of First Refusal shall terminate as to all Shares if the Company becomes a Publicly Listed Company upon such occurrence. 

6. Ownership, Voting Rights, Duties. This Agreement shall not affect in any way the ownership, voting rights or other rights or duties
of Purchaser, except as specifically provided herein. 
 7. Adjustment for Stock Split. All references to the number of Shares and
the purchase price of the Shares in this Agreement shall be appropriately adjusted to reflect any stock split, stock dividend or other change in the Shares which may be made by the Company after the date of this Agreement. 

  
 5 

 8. Notices. Notices required hereunder shall be given in person or by registered mail to
the address of Purchaser shown on the records of the Company, and to the Company at its principal executive office. 
 9. Survival of
Terms. This Agreement shall apply to and bind Purchaser and the Company and their respective permitted assignees and transferees, heirs, legatees, executors, administrators and legal successors. 

10. Section 83(b) Election for Unreleased Shares. Purchaser hereby acknowledges that he or she has been informed that, with
respect to the purchase of Unreleased Shares, that unless an election is filed by Purchaser with the Internal Revenue Service and, if necessary, the proper state taxing authorities, within thirty (30) days of the purchase of the Shares,
electing pursuant to Section 83(b) of the Code (and similar state tax provisions if applicable) to be taxed currently on any difference between the purchase price of the Shares and their Fair Market Value on the date of purchase, there will be
a recognition of taxable income to Purchaser, measured by the excess, if any, of the fair market value of the Shares, at the time the Company’s Repurchase Option lapses over the purchase price for the Shares. Purchaser represents that Purchaser
has consulted any tax consultant(s) Purchaser deems advisable in connection with the purchase of the Shares or the filing of the Election under Section 83(b) and similar tax provisions. 

PURCHASER ACKNOWLEDGES THAT IT IS PURCHASER’S SOLE RESPONSIBILITY AND NOT THE COMPANY’S TO FILE TIMELY THE ELECTION UNDER
SECTION 83(b), EVEN IF PURCHASER REQUESTS THE COMPANY OR ITS REPRESENTATIVE TO MAKE THIS FILING ON PURCHASER’S BEHALF. 
 11.
Representations. Purchaser has reviewed with his or her own tax advisors the federal, state, local and foreign tax consequences of this investment and the transactions contemplated by this Agreement. Purchaser is relying solely on such
advisors and not on any statements or representations of the Company or any of its agents. Purchaser understands that Purchaser (and not the Company) shall be responsible for his or her own tax liability that may arise as a result of this investment
or the transactions contemplated by this Agreement. 
 12. Restrictive Legends and Stop-Transfer Orders. 

12.1 Any share certificate(s) evidencing the Shares issued hereunder shall be endorsed with the following legends and any other legends that
may be required by state or federal securities laws: 
 THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A RIGHT OF REPURCHASE IN
FAVOR OF SIENNA BIOPHARMACEUTICALS, INC. (THE “COMPANY”) AND MAY BE TRANSFERRED ONLY IN ACCORDANCE WITH THE TERMS OF A RESTRICTED STOCK PURCHASE AGREEMENT BETWEEN THE COMPANY AND THE STOCKHOLDER, A COPY OF WHICH IS ON FILE WITH THE
SECRETARY OF THE COMPANY. 
 THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS

  
 6 

 
AMENDED (THE “ACT”), AND THEY HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE OR DISTRIBUTION THEREOF. NO SUCH SALE OR DISTRIBUTION MAY BE
EFFECTED WITHOUT AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL IN A FORM SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES ACT. 

THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A RIGHT OF FIRST REFUSAL IN FAVOR OF THE COMPANY AND/OR ITS ASSIGNEE(S) AND TRANSFER
RESTRICTIONS AS PROVIDED IN THE BYLAWS OF THE COMPANY THAT PROVIDES FOR TRANSFER RESTRICTIONS AT THE DISCRETION OF THE COMPANY. SUCH RIGHT OF FIRST REFUSAL AND TRANSFER RESTRICTIONS ARE BINDING UPON TRANSFEREES OF THESE SECURITIES. COPIES OF THE
BYLAWS OF THE COMPANY MAY BE OBTAINED UPON WRITTEN REQUEST TO THE SECRETARY OF THE COMPANY. 
 The Company may be authorized from time to
time pursuant to its certificate of incorporation to issue more than 1 class or series of stock. In such case and at any time or from time to time thereafter the Company will furnish without charge to you upon request the powers, designations,
preferences and relative participating, optional or other special rights of each class of stock or series thereof and the qualifications, limitations or restrictions of such preferences and/or rights. 

12.2 Purchaser agrees that, in order to ensure compliance with the restrictions referred to herein, the Company may issue appropriate
“stop transfer” instructions to its transfer agent, if any, and that, if the Company transfers its own securities, it may make appropriate notations to the same effect in its own records. 

12.3 The Company shall not be required: (i) to transfer on its books any Shares that have been sold or otherwise transferred in violation
of any of the provisions of this Agreement, or (ii) to treat as owner of such Shares or to accord the right to vote or pay dividends to any purchaser or other transferee to whom such Shares shall have been so transferred. 

12.4 To the extent the Shares are issued in uncertificated form, this Section 12 provides the Purchaser with notice that the Shares are
subject to the aforementioned restrictions in satisfaction of the notice requirement set forth in Section 151(f) of the Delaware General Corporation Law. 

13. Titles. Titles are provided herein for convenience only and are not to serve as a basis for interpretation or construction of this
Agreement. 

  
 7 

 14. Conformity to Securities Laws. Purchaser acknowledges that the Plan is intended to
conform to the extent necessary with all provisions of the Securities Act and the Exchange Act and any and all regulations and rules promulgated by the Securities and Exchange Commission thereunder, and state securities laws and regulations.
Notwithstanding anything herein to the contrary, the Plan shall be administered, and the Shares are to be issued, only in such a manner as to conform to such laws, rules and regulations. To the extent permitted by applicable law, the Plan and this
Agreement shall be deemed amended to the extent necessary to conform to such laws, rules and regulations. Purchaser shall not transfer in any manner the Shares issued pursuant to this Agreement, without regard to whether such Shares are no longer
subject to the Repurchase Option, unless (i) the transfer is pursuant to an effective registration statement under the Securities Act, or the rules and regulations in effect thereunder or (ii) counsel for the Company shall have reasonably
concluded that no such registration is required because of the availability of an exemption from registration under the Securities Act. 

15. Lock-Up Period. Purchaser hereby agrees that if so requested by the Company or any representative of the underwriters (the
“Managing Underwriter”) in connection with any registration of the offering of any securities of the Company under the Securities Act, Purchaser shall not, directly or indirectly, sell or otherwise transfer any Shares or other
securities of the Company during a period of up to 180 days (the “Lock-Up Period”) following the effective date of a registration statement of the Company filed under the Securities Act; provided, however, that such restriction
shall apply only to the first registration statement of the Company to become effective under the Securities Act that includes securities to be sold on behalf of the Company to the public in an underwritten public offering under the Securities Act.
The Company may impose stop-transfer instructions with respect to securities subject to the foregoing restrictions until the end of such Lock-Up Period and these restrictions shall be binding on any transferee
of such Shares. Notwithstanding the foregoing, the 180-day period may be extended for up to such number of additional days as is deemed necessary by the Company or the Managing Underwriter to continue coverage by research analysts in accordance with
NASD Rule 2711 or any successor rule. 
 16. Further Instruments. Purchaser hereby agrees to execute such further instruments and to
take such further action as may be reasonably necessary to carry out the purposes and intent of this Agreement including, without limitation, the Investment Representation Statement, in the form attached to the Grant Notice as Exhibit E. 

17. Governing Law; Severability. This Agreement shall be governed by and construed in accordance with the laws of the State of Delaware
excluding that body of law pertaining to conflicts of law. Should any provision of this Agreement be determined by a court of law to be illegal or unenforceable, the other provisions shall nevertheless remain effective and shall remain enforceable.

 18. Rules Particular To Specific Countries. 

18.1 Generally. Purchaser shall, if required by the Administrator, enter into an election with the Company or a subsidiary (in a form
approved by the Company) under which any liability to the Company’s (or a subsidiary’s) Tax Liability, including, but not limited to, National Insurance Contributions (“NICs”) and Fringe Benefit Tax
(“FBT”), is transferred to and 

  
 8 

 
met by Purchaser. For purposes of this Section 18, Tax Liability shall mean any and all liability under applicable non-U.S. laws, rules or regulations from any income tax, the Company’s
(or a subsidiary’s) NICs, FBT or similar liability and Purchaser’s NICs, FBT or similar liability under non-U.S. laws that are attributable to: (A) the grant of, or any other benefit derived by the Purchaser from the Shares;
(B) the acquisition by Purchaser of the Shares; or (C) the disposal of any Shares acquired. 
 18.2 Tax Indemnity.
Purchaser shall indemnify and keep indemnified the Company and any of its subsidiaries from and against any Tax Liability. 

*     *     *     *     * 

  
 9 

 Exhibit B 

STOCK ASSIGNMENT 
 FOR VALUE
RECEIVED I,                 , hereby sell, assign and transfer unto
                                         
    (                ) shares of the Common Stock of Sienna Biopharmaceuticals, Inc. registered in my name on the books of said corporation
[represented by Certificate No.              herewith] and do hereby irrevocably constitute and appoint
                                         
    to transfer the said stock on the books of the within named corporation with full power of substitution in the premises. 

This Stock Assignment may be used only in accordance with the Restricted Stock Purchase Agreement between Sienna Biopharmaceuticals, Inc. and
the undersigned dated                 ,             . 

Dated:                     ,
             
  

					
	Signature:	 	  

 INSTRUCTIONS: Please do not fill in any blanks other than the signature line. The purpose of this assignment
is to enable the Company to exercise the Repurchase Option, as set forth in the Restricted Stock Purchase Agreement, without requiring additional signatures on the part of Purchaser. 

 Exhibit C 

JOINT ESCROW INSTRUCTIONS 

                    ,
             
 Secretary 

Sienna Biopharmaceuticals, Inc. 
 [Address] 

[Address] 
 Dear Secretary, 

As Escrow Agent for both Sienna Biopharmaceuticals, Inc. (the “Company”) and the undersigned purchaser of stock of the
Company (the “Purchaser”), you are hereby authorized and directed to hold the documents delivered to you pursuant to the terms of that certain Restricted Stock Purchase Agreement (“Agreement”) between the Company
and the undersigned, in accordance with the following instructions: 
 1. In the event the Company or any entitled parties (referred to
collectively for convenience herein as the “Company”) exercises the Company’s Repurchase Option set forth in the Agreement, the Company shall give to Purchaser and you a written notice specifying the number of shares of stock
to be purchased, the purchase price, and the time for a closing hereunder at the principal office of the Company. Purchaser and the Company hereby irrevocably authorize and direct you to close the transaction contemplated by such notice in
accordance with the terms of said notice. 
 2. At the closing, you are directed (a) to date the stock assignments necessary for the
transfer in question, (b) to fill in the number of shares being transferred, and (c) to deliver the same, together with any certificate evidencing the shares of stock to be transferred, to the Company or its assignee, against the
simultaneous delivery to you of the purchase price (by cash, a check, or a combination thereof) for the number of shares of stock being purchased pursuant to the exercise of the Company’s Repurchase Option. 

3. Purchaser irrevocably authorizes the Company to deposit with you any certificates evidencing shares of stock to be held by you hereunder
and any additions and substitutions to said shares as defined in the Agreement. Purchaser does hereby irrevocably constitute and appoint you as Purchaser’s attorney-in-fact and agent for the term of this escrow to execute, with respect to such
securities, all documents necessary or appropriate to make such securities negotiable and to complete any transaction herein contemplated, including but not limited to the filing with any applicable state blue sky authority of any required
applications for consent to, or notice of transfer of, the securities. Subject to the provisions of this paragraph 3 and to the terms of the Agreement, Purchaser shall exercise all rights and privileges of a stockholder of the Company while the
stock is held by you. 

 4. Upon written request of Purchaser, but no more than once per calendar year, unless the
Company’s Repurchase Option has been exercised, you will deliver to Purchaser a certificate or certificates (only if the shares are in certificated form) representing the number of shares of stock as are not then subject to the Company’s
Repurchase Option or will provide Participant evidence that such shares have been duly entered into the records of the Company. Within one hundred twenty (120) days after Purchaser ceases to be a Service Provider, you will deliver to Purchaser
a certificate or certificates representing the aggregate number of shares held or issued pursuant to the Agreement and not purchased by the Company or any other entitled parties pursuant to exercise of the Company’s Repurchase Option or will
provide Participant evidence that such shares have been duly entered into the records of the Company. 
 5. If at the time of termination of
this escrow you should have in your possession any documents, securities, or other property belonging to Purchaser, you shall deliver all of the same to Purchaser and shall be discharged of all further obligations hereunder. 

6. Your duties hereunder may be altered, amended, modified or revoked only by a writing signed by all of the parties hereto. 

7. You shall be obligated only for the performance of such duties as are specifically set forth herein and may rely and shall be protected in
relying or refraining from acting on any instrument reasonably believed by you to be genuine and to have been signed or presented by the proper party or parties. You shall not be personally liable for any act you may do or omit to do hereunder as
Escrow Agent or as attorney-in-fact for Purchaser while acting in good faith, and any act done or omitted by you pursuant to the advice of your own attorneys shall be conclusive evidence of such good faith. 

8. You are hereby expressly authorized to disregard any and all warnings given by any of the parties hereto or by any other person or
corporation, excepting only orders or process of courts of law and are hereby expressly authorized to comply with and obey orders, judgments or decrees of any court. In case you obey or comply with any such order, judgment or decree, you shall not
be liable to any of the parties hereto or to any other person, firm or corporation by reason of such compliance, notwithstanding any such order, judgment or decree being subsequently reversed, modified, annulled, set aside, vacated or found to have
been entered without jurisdiction. 
 9. You shall not be liable in any respect on account of the identity, authorities or rights of the
parties executing or delivering or purporting to execute or deliver the Agreement or any documents or papers deposited or called for hereunder. 

10. You shall not be liable for the expiration of any rights under any applicable state, federal or local statute of limitations or similar
statute or regulation with respect to these Joint Escrow Instructions or any documents deposited with you. 
 11. You shall be entitled to
employ such legal counsel and other experts as you may deem necessary properly to advise you in connection with your obligations hereunder, may rely upon the advice of such counsel, and may pay such counsel reasonable compensation therefor. 

 12. Your responsibilities as Escrow Agent hereunder shall terminate if you shall cease to be an
officer or agent of the Company or if you shall resign by written notice to each party. In the event of any such termination, the Company shall appoint a successor Escrow Agent. 

13. If you reasonably require other or further instruments in connection with these Joint Escrow Instructions or obligations in respect
hereto, the necessary parties hereto shall join in furnishing such instruments. 
 14. It is understood and agreed that should any dispute
arise with respect to the delivery and/or ownership or right of possession of the securities held by you hereunder, you are authorized and directed to retain in your possession without liability to anyone all or any part of said securities until
such disputes shall have been settled either by mutual written agreement of the parties concerned or by a final order, decree or judgment of a court of competent jurisdiction after the time for appeal has expired and no appeal has been perfected,
but you shall be under no duty whatsoever to institute or defend any such proceedings. 
 15. Any notice required or permitted hereunder
shall be given in writing and shall be deemed effectively given upon personal delivery or upon deposit in the United States Post Office, by registered or certified mail with postage and fees prepaid, addressed to each of the other parties thereunto
entitled at such addresses as a party may designate by written notice to each of the other parties hereto. 
 16. By signing these Joint
Escrow Instructions, you become a party hereto only for the purpose of said Joint Escrow Instructions; you do not become a party to the Agreement. 

17. This instrument shall be binding upon and inure to the benefit of the parties hereto, and their respective successors and permitted
assigns. 
 18. These Joint Escrow Instructions shall be governed by, and construed and enforced in accordance with, the laws of the State
of Delaware, excluding that body of law pertaining to conflicts of law. 
 (Signature Page Follows) 

 IN WITNESS WHEREOF, these Joint Escrow Instructions shall be effective as of the date first set
forth above. 
  

			
	SIENNA BIOPHARMACEUTICALS, INC.
		
	By:	 	                                      
                                         
           
		
		 	Name:                                     
                                        

		
		 	Title:                                     
                                         
  
	
	PURCHASER
		
	By:	 	  

	Name:	 	  

	
	Address:
	
	  

	  

	
	ESCROW AGENT
		
	By:	 	  

		
	Name:	 	  

		
	Title:	 	  

 Exhibit D 

CONSENT OF SPOUSE OR DOMESTIC PARTNER 

I,                     , spouse or
registered domestic partner of                     , have read and approve the Restricted Stock Purchase Agreement dated
                ,             , between my spouse or registered domestic partner and Sienna
Biopharmaceuticals, Inc. In consideration of granting of the right to my spouse or registered domestic partner to purchase shares of common stock of Sienna Biopharmaceuticals, Inc. set forth in the Restricted Stock Purchase Agreement, I hereby
appoint my spouse or registered domestic partner as my attorney-in-fact in respect to the exercise of any rights under the Agreement and agree to be bound by the provisions of the Restricted Stock Purchase Agreement insofar as I may have any rights
in said Restricted Stock Purchase Agreement or any shares issued pursuant thereto under the community property laws or similar laws relating to marital property in effect in the state of our residence as of the date of the signing of the foregoing
Restricted Stock Purchase Agreement. 
 Dated:
                    ,              

 

	
	  

	Signature of Spouse or Registered Domestic Partner

 Exhibit E 

INVESTMENT REPRESENTATION STATEMENT 
  

					
	PURCHASER	 	:	 	
			
	COMPANY	 	:	 	    Sienna Biopharmaceuticals, Inc.
			
	SECURITY	 	:	 	    Common Stock
			
	AMOUNT	 	:	 	
			
	DATE	 	:	 	

 In connection with the purchase of the above-listed shares of Common Stock (the “Securities”)
of Sienna Biopharmaceuticals, Inc., a Delaware corporation (f/k/a Sienna Labs, Inc., the “Company”), the undersigned (“Purchaser”) represents to the Company the following: 

1. Purchaser is aware of the Company’s business affairs and financial condition and has acquired sufficient information about the Company
to reach an informed and knowledgeable decision to acquire the Securities. Purchaser is acquiring these Securities for investment for Purchaser’s own account only and not with a view to, or for resale in connection with, any
“distribution” thereof within the meaning of the Securities Act of 1933, as amended (the “Securities Act”). 
 2.
Purchaser acknowledges and understands that the Securities constitute “restricted securities” under the Securities Act and have not been registered under the Securities Act in reliance upon a specific exemption therefrom, which exemption
depends upon, among other things, the bona fide nature of Purchaser’s investment intent as expressed herein. Purchaser understands that, in the view of the Securities and Exchange Commission, the statutory basis for such exemption may be
unavailable if Purchaser’s representation was predicated solely upon a present intention to hold these Securities for the minimum capital gains period specified under tax statutes, for a deferred sale, for or until an increase or decrease in
the market price of the Securities, or for a period of one year or any other fixed period in the future. Purchaser further understands that the Securities must be held indefinitely unless they are subsequently registered under the Securities Act or
an exemption from such registration is available. Purchaser further acknowledges and understands that the Company is under no obligation to register the Securities. Purchaser understands that any certificate evidencing the Securities will be
imprinted with a legend which prohibits the transfer of the Securities unless they are registered or such registration is not required in the opinion of counsel satisfactory to the Company and any other legend required under applicable state
securities laws or agreements. 
 3. Purchaser is familiar with the provisions of Rule 701 and Rule 144, each promulgated under
the Securities Act, which, in substance, permit limited public resale of “restricted securities” acquired, directly or indirectly from the issuer thereof, in a non-public offering subject to the satisfaction of certain conditions.
Rule 701 provides that if the issuer 

 
qualifies under Rule 701 at the time of the grant of the Stock Purchase Right to Purchaser, the exercise will be exempt from registration under the Securities Act. In the event the Company
becomes subject to the reporting requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), ninety (90) days thereafter (or such longer period as any market stand-off
agreement may require) the Securities exempt under Rule 701 may under present law be resold, subject to the satisfaction of certain of the conditions specified by Rule 144, including: (1) the resale being made through a broker in an
unsolicited “broker’s transaction” or in transactions directly with a market maker (as said term is defined under the Exchange Act); and, in the case of an affiliate, (2) the availability of certain public information about
the Company, (3) the amount of Securities being sold during any three (3) month period not exceeding the limitations specified in Rule 144(e), and (4) the timely filing of a Form 144, if applicable. 

In the event that the Company does not qualify under Rule 701 at the time of grant of the Stock Purchase Right, then the Securities may
be resold in certain limited circumstances subject to the provisions of Rule 144, which requires the resale to occur not less than six months, or, in the event the Company is not subject to the reporting requirements of Section 13 or
15(d) of the Securities Exchange Act of 1934, not less than one year, after the later of the date the Securities were sold by the Company or the date the Securities were sold by an affiliate of the Company, within the meaning of Rule 144; and,
in the case of acquisition of the Securities by an affiliate, the satisfaction of the conditions set forth in sections (1), (2), (3) and (4) of the paragraph immediately above or, in the case of a non-affiliate who subsequently holds the
Securities less than one year, the satisfaction of the conditions set forth in section (2) of the paragraph immediately above.. 
 4.
Purchaser further understands that in the event all of the applicable requirements of Rule 701 or 144 are not satisfied, registration under the Securities Act, compliance with Regulation A, or some other registration exemption will be required;
and that, notwithstanding the fact that Rules 144 and 701 are not exclusive, the Staff of the Securities and Exchange Commission has expressed its opinion that persons proposing to sell private placement securities other than in a registered
offering and otherwise than pursuant to Rules 144 or 701 will have a substantial burden of proof in establishing that an exemption from registration is available for such offers or sales, and that such persons and their respective brokers who
participate in such transactions do so at their own risk. Purchaser understands that no assurances can be given that any such other registration exemption will be available in such event. 

 

	
	Signature of Purchaser:
	
	  

	[Purchaser]

 Date:
                    ,          

  
 2 

 FORM OF 83(B) ELECTION AND INSTRUCTIONS 

These instructions are provided to assist you if you choose to make an election under Section 83(b) of the Internal Revenue Code, as
amended, with respect to the shares of common stock of Sienna Biopharmaceuticals, Inc. transferred to you. Please consult with your personal tax advisor as to whether an election of this nature will be in your best interests in light of your
personal tax situation. 
 The executed original of the Section 83(b) election must be filed with the Internal Revenue Service not
later than 30 days after the date the shares were transferred to you. PLEASE NOTE: There is no remedy for failure to file on time. The steps outlined below should be followed to ensure the election is mailed and filed correctly and in a timely
manner. ALSO, PLEASE NOTE: If you make the Section 83(b) election, the election is irrevocable. 
 Complete Section 83(b) election
form (attached as Attachment 1) and make four (4) copies of the signed election form. (Your spouse, if any, should sign the Section 83(b) election form as well.) 

Prepare the cover letter to the Internal Revenue Service (sample letter attached as Attachment 2). 

Send the cover letter with the originally executed Section 83(b) election form and one (1) copy via certified mail, return receipt
requested to the Internal Revenue Service at the address of the Internal Revenue Service where you file your personal tax returns. We suggest that you have the package date-stamped at the post office. The post office will provide you with a
certified receipt that includes a dated postmark. Enclose a self-addressed, stamped envelope so that the Internal Revenue Service may return a date-stamped copy to you. However, your postmarked receipt is your proof of having timely filed the
Section 83(b) election if you do not receive confirmation from the Internal Revenue Service. 
 One (1) copy must be sent to
Sienna Biopharmaceuticals, Inc. for its records and one (1) copy must be attached to your federal income tax return for the applicable calendar year. 

Retain the Internal Revenue Service file stamped copy (when returned) for your records. 

Please consult your personal tax advisor for the address of the office of the Internal Revenue Service to which you should mail your election
form. 

 ATTACHMENT 1 

ELECTION UNDER INTERNAL REVENUE CODE SECTION 83(B) 

The undersigned taxpayer hereby elects, pursuant to Section 83(b) of the Internal Revenue Code of 1986, as amended, to include in
taxpayer’s gross income for the current taxable year the amount of any compensation taxable to taxpayer in connection with taxpayer’s receipt of shares (the “Shares”) of Common Stock of Sienna Biopharmaceuticals, Inc., a
Delaware corporation (f/k/a Sienna Labs, Inc., the “Company”). 
 The name, address and taxpayer identification number of the undersigned
taxpayer are: 
  

					
		 	  
	  	
		 	  
	  	
		 	  
	  	
			
		 	SSN:                                     
                                         
       	  	

 The name, address and taxpayer identification number of the Taxpayer’s spouse are (complete if
applicable): 
  

					
		 	  
	  	
		 	  
	  	
		 	  
	  	
			
		 	SSN:                                     
                                         
       	  	

 Description of the property with respect to which the election is being made: 

                    
(            ) shares of Common Stock of the Company. 
 The date on which the property
was transferred was                     . The taxable year to        which this election relates is
calendar year             . 
 Nature of restrictions to which the property is subject:

 The Shares are subject to repurchase by the Company or its assignee upon the occurrence of certain events. This repurchase right lapses
based upon the continued performance of services by the taxpayer over time. 
 The fair market value at the time of transfer (determined without regard to
any lapse restrictions,        as defined in Treasury Regulation Section 1.83-3(i)) of the Shares was
$            per        Share. 
 The amount paid
by the taxpayer for Shares was $             per share. 
 A copy of this statement has
been furnished to the Company. 
  

			
	Dated:                     ,         	  	Taxpayer
Signature                                 

 The undersigned spouse of Taxpayer joins in this election. (Complete if applicable). 

 

			
	Dated:                     ,         	  	Spouse’s Signature
                                         
           
		
	Signature(s) Notarized by:	  	
		
	
                   
                                         
        
	  	
		
	
                   
                                         
        
	  	

 ATTACHMENT 2 

SAMPLE COVER LETTER TO INTERNAL REVENUE SERVICE 

                    ,
             
 VIA CERTIFIED MAIL 

RETURN RECEIPT REQUESTED 
 Internal Revenue
Service 
 [Address where taxpayer files returns] 
  

					
	Re:	  	Election under Section 83(b) of the Internal Revenue Code of 1986	  	
		  	Taxpayer:                                    
                                         
                                         
                                         
                  	  	
		  	Taxpayer’s Social Security
Number:                                        
                                         
                                         
     	  	
		  	Taxpayer’s
Spouse:                                        
                                         
                                         
                                     	  	
		  	Taxpayer’s Spouse’s Social Security
Number:                                        
                                         
                            	  	

 Ladies and Gentlemen: 

Enclosed please find an original and one copy of an Election under Section 83(b) of the Internal Revenue Code of 1986, as amended, being
made by the taxpayer referenced above. Please acknowledge receipt of the enclosed materials by stamping the enclosed copy of the Election and returning it to me in the self-addressed stamped envelope provided herewith. 

 

	
	Very truly yours,
	
	  

 Enclosures

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