Document:

EX-10.2

 Exhibit 10.2 

SIENNA BIOPHARMACEUTICALS, INC. 

EMPLOYMENT AGREEMENT 

This Employment Agreement (the “Agreement”), is made by and between Sienna Biopharmaceuticals, Inc., a Delaware corporation
(the “Company”) and Alexander Azoy (“Executive” and, together with the Company, the “Parties”), effective as of April 1, 2019 (the “Effective Date”). This Agreement supersedes
in its entirety that certain offer letter by and between Executive and the Company dated as of November 7, 2017 (the “Prior Agreement”). 

WHEREAS, the Company desires to assure itself of the continued services of Executive by engaging Executive to perform services
as an employee of the Company under the terms hereof; 
 WHEREAS, Executive desires to provide continued services to the Company on
the terms herein provided; and 
 WHEREAS, the Parties desire to execute this Agreement to supersede in its entirety the Prior
Agreement and reflect certain changes to Executive’s employment with the Company effective as of the Effective Date. 
 NOW,
THEREFORE, in consideration of the foregoing, and for other good and valuable consideration, including the respective covenants and agreements set forth below, the receipt and sufficiency of which are hereby acknowledged, the Parties hereto
agree as follows: 
 1.    Employment. 

(a)    General. The Company shall employ Executive upon the terms and conditions provided herein effective as of the
Effective Date. 
 (b)    Position and Duties. Effective on the Effective Date, Executive: (i) shall serve as
the Company’s Chief Financial Officer, with responsibilities, duties, and authority usual and customary for such position, subject to direction by the Chief Executive Officer of the Company (the “CEO”); (ii) shall report
directly to the CEO; and (iii) agrees promptly and faithfully to comply with all present and future policies, requirements, rules and regulations, and reasonable directions and requests, of the Company in connection with the Company’s
business. At the Company’s request, Executive shall serve the Company and/or its subsidiaries and affiliates in such other capacities in addition to the foregoing as the Company shall designate, provided that such additional capacities are
consistent with Executive’s position as the Company’s Chief Financial Officer. In the event that Executive serves in any one or more of such additional capacities, Executive’s compensation shall not automatically be increased on
account of such additional service. 
 (c)    Performance of Executive’s Duties. During Executive’s
employment with the Company, and except for periods of illness, vacation, disability, or reasonable leaves of absence or as discussed in Section 1(d) below, Executive shall devote Executive’s full time and attention to the business and
affairs of the Company pursuant to the general direction of the CEO. The rights of Executive under this Agreement shall not be affected by any change in the title, duties, or capacity of Executive during Executive’s employment with the Company.

  
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 (d)    Exclusivity. Except with the prior written approval of the
CEO (which the CEO may grant or withhold in his or her sole and absolute discretion), Executive shall devote substantially all of Executive’s working time, attention, and energies to the business of the Company, except during any paid vacation
or other excused absence periods. Nothing in this section prevents Executive from (i) engaging in additional activities in connection with personal investments and community affairs including service on
non-profit boards of directors, (ii) serving as a member of the board of directors of up to two (2) for-profit organizations that are not competitors of the
Company (or such greater number as approved by the CEO), and (iii) serving as an advisor, or as a member of an advisory board, to up to two (2) organizations that are not competitors of the Company (or such greater number as approved by
the CEO); provided such activities do not individually or in the aggregate interfere with the performance of Executive’s duties under this Agreement, violate the Company’s standards of conduct then in effect, or raise a conflict under the
Company’s conflict of interest policies. 
 2.    Term. The period of Executive’s
employment under this Agreement shall commence on the Effective Date and shall continue until Executive’s employment with the Company is terminated pursuant to Section 5 below. The phrase “Term of Employment” as used in
this Agreement shall refer to the entire period of employment of Executive by the Company. 

3.    Compensation and Related Matters. 

(a)    Annual Base Salary. Executive shall receive a base salary at the rate of $300,000 per annum (as may be
increased from time to time, the “Annual Base Salary”), subject to withholdings and deductions, which shall be paid to Executive in accordance with the customary payroll practices and procedures of the Company. Such Annual Base
Salary shall be reviewed by the CEO, and as applicable, the Board of Directors of the Company (the “Board”), not less than annually, and may be increased, but not decreased, in connection with any such review. 

(b)    Annual Bonus. Executive shall be eligible to receive a discretionary annual bonus based on Executive’s
achievement of performance objectives as mutually agreed between Executive and the CEO, such bonus to be targeted at thirty-five percent (35%) of Executive’s Annual Base Salary (the “Annual Bonus”). Any Annual Bonus earned will
be paid at the same time annual bonuses are paid to other executives of the Company generally, subject to Executive’s continuous employment through the date of payment. 

(c)    Benefits. Executive shall be entitled to participate in such employee and executive benefit plans and
programs as the Company may from time to time offer to provide to its executives, subject to the terms and conditions of such plans. Notwithstanding the foregoing, nothing herein is intended, or shall be construed, to require the Company to
institute or continue any, or any particular, plan, or benefits. 
 (d)    Business Expenses. The Company shall
reimburse Executive for all reasonable, documented, out-of-pocket travel and other business expenses incurred by Executive in the performance of Executive’s duties
to the Company in accordance with the Company’s applicable expense reimbursement policies and procedures as are in effect from time to time. 

  
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 (e)    Vacation. Executive will be entitled to not less than
fifteen (15) business days of paid vacation each calendar year, pro-rated for partial calendar years of service, which may be taken in accordance with the Company’s vacation policy. 

(f)    Equity Awards. Executive shall be eligible to receive grants of equity awards in the Company’s sole
discretion. 
 (g)    Indemnification Agreement; Insurance. As an officer of the Company, Executive shall be
entitled to enter into the Company’s standard indemnification agreement. Executive will also be covered under a directors and officers liability insurance policy paid for by the Company for so long as Executive serves as an officer of the
Company. 
 4.    Acceleration of Equity Awards Upon a Change in Control. Notwithstanding anything
herein to the contrary, in the event of a Change in Control (as defined below), the vesting of Executive’s then outstanding options, restricted stock and other equity awards covering shares of the Company’s common stock (collectively,
“Equity Awards”) shall accelerate as of immediately prior to such Change in Control with respect to 50% of the unvested shares of Company common stock subject to such Equity Awards. The remaining 50% of the unvested shares of
Company common stock subject to Executive’s Equity Awards shall continue to vest at the same rate as immediately prior to the Change in Control, subject to Executive’s continued service to the Company or its successor through the
applicable vesting date. Any portion of Executive’s Equity Awards that remains unvested as of the first anniversary of the Change in Control shall thereupon vest in full, subject to Executive’s continued service to the Company or its
successor through such first anniversary. Notwithstanding the foregoing and for the avoidance of doubt, any shares subject to Equity Awards that do not accelerate immediately prior to the Change in Control in accordance with the foregoing shall be
subject to accelerated vesting in accordance with Section 6(c)(iii) below. 
 5.    Termination.

(a)    At-Will Employment. The Company and Executive acknowledge that
Executive’s employment shall be at-will, as defined under applicable law. This means that it is not for any specified period of time and can be terminated by Executive or by the Company at any time, with
or without advance notice, and for any or no particular reason or cause. It also means that Executive’s job duties, title, and responsibility and reporting level, work schedule, compensation, and benefits, as well as the Company’s
personnel policies and procedures, may be changed with prospective effect, with or without notice, at any time in the sole discretion of the Company (subject to any ramification such changes may have under Section 6 of this Agreement). This “at-will” nature of Executive’s employment shall remain unchanged during Executive’s tenure as an employee and may not be changed, except in an express writing signed by Executive and the CEO. If
Executive’s employment terminates for any lawful reason, Executive shall not be entitled to any payments, benefits, damages, award, or compensation other than as provided in this Agreement. 

(b)    Notice of Termination. During the Term of Employment, any termination of Executive’s employment by the
Company or by Executive (other than by reason of death) shall be communicated by written notice (a “Notice of Termination”) from one Party hereto to the other 

  
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Party hereto (i) indicating the specific termination provision in this Agreement relied upon, if any, (ii) setting forth in reasonable detail the facts and circumstances claimed to
provide a basis for termination of Executive’s employment under the provision so indicated, and (iii) specifying the Date of Termination (as defined below). The failure by the Company to set forth in the Notice of Termination all of the
facts and circumstances which contribute to a showing of Cause (as defined below) shall not waive any right of the Company hereunder or preclude the Company from asserting such fact or circumstance in enforcing their rights hereunder. The failure by
Executive to set forth in the Notice of Termination all of the facts and circumstances which contribute to a showing of Good Reason (as defined below) shall not waive any right of Executive hereunder or preclude Executive from asserting such fact or
circumstance in enforcing their rights hereunder. 
 (c)    Termination Date. For purposes of this Agreement,
“Date of Termination” shall mean the date of the termination of Executive’s employment with the Company specified in a Notice of Termination. 

(d)    Deemed Resignation. Upon termination of Executive’s employment for any reason, Executive shall be deemed
to have resigned from all offices and board memberships, if any, then held with the Company or any of its affiliates, and, at the Company’s request, Executive shall execute such documents as are necessary or desirable to effectuate such
resignations. 
 6.    Consequences of Termination. 

(a)    Payments of Accrued Obligations upon all Terminations of Employment. Upon a termination of Executive’s
employment for any reason, Executive (or Executive’s estate or legal representative, as applicable) shall be entitled to receive, within thirty (30) days after Executive’s Date of Termination (or such earlier date as may be required
by applicable law): (i) any portion of Executive’s Annual Base Salary earned through Executive’s Date of Termination not theretofore paid, (ii) any expenses owed to Executive under Section 3(d) above, (iii) any accrued but
unused paid time-off owed to Executive, (iv) any Annual Bonus earned but unpaid as of the Date of Termination, and (v) any amount arising from Executive’s participation in, or benefits under,
any employee benefit plans, programs, or arrangements under Section 3(c) above, which amounts shall be payable in accordance with the terms and conditions of such employee benefit plans, programs, or arrangements. Except as otherwise set forth
in Sections 6(b) and 6(c) below, the payments and benefits described in this Section 6(a) shall be the only payments and benefits payable in the event of Executive’s termination of employment for any reason. 

  
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 (b)    Severance Payments upon Involuntary Termination Other Than
During a Change in Control Period. If, during the Term of Employment but outside of a Change in Control Period (as defined below), Executive’s employment is terminated due to an Involuntary Termination (as defined below), in addition to the
payments and benefits described in Section 6(a) above, the Company shall provide the following payments and benefits, subject to delivery to the Company by Executive (or Executive’s estate or representative in the case of death or
Disability (as defined below)) of a waiver and release of claims agreement in a standard form approved by the Company that becomes effective and irrevocable in accordance with Section 11(d) hereof (a “Release”): 

(i)    Executive shall be entitled to receive an amount equal to six months of Executive’s then-existing base salary
in effect as of Executive’s termination date, less applicable withholdings, payable in a lump sum on the first regular payroll date following the date of Executive’s Release becomes effective and irrevocable or as otherwise provided in
Section 11(d) hereof. 
 (ii)    During the period commencing on the Date of Termination and ending on the six-month anniversary thereof or, if earlier, the date on which Executive becomes eligible for comparable replacement coverage under a subsequent employer’s group health plan, subject to Executive’s valid
election to continue healthcare coverage under Section 4980B of the Internal Revenue Code of 1986, as amended (the “Code”) and the regulations thereunder (“COBRA”), the Company shall, in its sole discretion,
either (A) continue to provide to Executive and Executive’s dependents, at the Company’s sole expense, or (B) reimburse Executive and Executive’s dependents for the cost of, in either case, coverage under its group health
plan (if any) at the same coverage levels in effect on the Date of Termination (“Benefits Coverage”); provided, however, that if (1) any plan pursuant to which such benefits are provided is not, or ceases prior to the
expiration of the continuation coverage period to be, exempt from the application of Section 409A under Treasury Regulation Section 1.409A-1(a)(5), (2) the Company is otherwise unable to continue to
cover Executive or Executive’s dependents under its group health plans, or (3) the Company cannot provide the benefit without violating applicable law (including, without limitation, Section 2716 of the Public Health Service Act),
then, in any such case, the cash amount necessary to maintain the Benefits Coverage shall thereafter be paid to Executive in substantially equal monthly installments over the COBRA continuation period (or remaining portion thereof). 

(c)    Severance Payments upon Involuntary Termination During a Change in Control Period. If, during the Term of
Employment and during a Change in Control Period, Executive’s employment is terminated due to an Involuntary Termination, in addition to the payments and benefits described in Section 6(a) above, the Company shall provide the following
payments and benefits, subject to delivery by Executive (or Executive’s estate or representative in the case of death or Disability) to the Company of a Release that becomes effective and irrevocable in accordance with Section 11(d)
hereof: 
 (i)    The Company shall pay to Executive an amount equal to (i) twelve months of Executive’s
Annual Base Salary plus (ii) Executive’s target Annual Bonus plus (iii) Executive’s target Annual Bonus, pro-rated based on the total number of days elapsed in the calendar year as of
Executive’s Date of Termination. Such amount will be subject to applicable withholdings and payable in a single lump sum cash payment on the first regular payroll date following the date the Release becomes effective and irrevocable or as
otherwise provided in Section 11(d) hereof. 
 (ii)    During the period commencing on the Date of Termination and
ending on the first anniversary thereof or, if earlier, the date on which Executive becomes eligible for comparable replacement coverage under a subsequent employer’s group health plan, subject to Executive’s valid election to continue
healthcare coverage under COBRA, the Company shall, in its sole discretion, either (A) continue to provide to Executive and Executive’s dependents, at the Company’s sole expense, or (B) reimburse Executive and Executive’s
dependents for the cost of, in either case, the Benefits Coverage; provided, however, that if (1) any plan pursuant to which 

  
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such benefits are provided is not, or ceases prior to the expiration of the continuation coverage period to be, exempt from the application of Section 409A under Treasury Regulation Section 1.409A-1(a)(5), (2) the Company is otherwise unable to continue to cover Executive or Executive’s dependents under its group health plans, or (3) the Company cannot provide the benefit without
violating applicable law (including, without limitation, Section 2716 of the Public Health Service Act), then, in any such case, the cash amount necessary to maintain the Benefits Coverage shall thereafter be paid to Executive in substantially
equal monthly installments over the COBRA continuation period (or remaining portion thereof). 
 (iii)    Any unvested
Equity Awards held by Executive as of the Date of Termination, will become fully vested and, if applicable, exercisable, and all restrictions and rights of repurchase thereon shall lapse with respect to all of the shares of the Company’s common
stock subject thereto. 
 (d)    No Other Severance. The provisions of this Section 6 shall supersede in
their entirety any severance payment provisions in any severance plan, policy, program, or other arrangement maintained by the Company except for such additional benefits otherwise approved by the Board or Compensation Committee of the Board after
the date hereof. 
 (e)    No Requirement to Mitigate; Survival. Executive shall not be required to mitigate the
amount of any payment provided for under this Agreement by seeking other employment or in any other manner. Notwithstanding anything to the contrary in this Agreement, the termination of Executive’s employment shall not impair the rights or
obligations of any Party. 
 (f)    Definition of Cause. For purposes hereof, “Cause” shall mean
any one of the following: (i) Executive’s willful or reckless violation of any applicable material law or regulation respecting the business of the Company; (ii) Executive’s conviction of, or plea of nolo contendere to, a non-vehicular felony or other crime involving moral turpitude; (iii) any act of dishonesty, fraud, or misrepresentation in relation to Executive’s duties to the Company which act is materially and
demonstrably injurious to the Company; (iv) Executive’s willful and repeated failure to perform in any material respect Executive’s duties; (v) Executive’s failure to attempt in good faith to implement a clear and reasonable
directive from the CEO or to comply with any of the Company’s policies and procedures which failure is either material or occurs after written notice from the Board; (vi) any act of gross misconduct which is materially and demonstrably
injurious to the Company; or (vii) Executive’s breach of fiduciary duty owed to the Company; provided that in the cases of (iv)-(vii), Executive is given written notice within fifteen (15) days’ notice of the occurrence and an
opportunity to cure any such failure that is subject to cure, including a reasonable opportunity to present to the Board Executive’s position regarding any dispute relating to the existence of such failure (other than on account of disability).

 (g)    Definition of Change in Control. For purposes hereof, “Change in Control” shall mean
and includes each of the following: 
 (i)    A transaction or series of transactions (other than an
offering of Company common stock to the general public through a registration statement filed with the Securities and Exchange Commission) whereby any “person” or related “group” of “persons” (as such terms are used in
Sections 13(d) and 14(d)(2) of the Securities and 

  
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Exchange Act of 1934, as amended (the “Exchange Act”)) directly or indirectly acquires beneficial ownership (within the meaning of Rules
13d-3 and 13d-5 under the Exchange Act) of securities of the Company possessing more than 50 % of the total combined voting power of the Company’s securities
outstanding immediately after such acquisition; provided, however, that the following acquisitions shall not constitute a Change in Control: (x) any acquisition by the Company or any of its subsidiaries; (y) any acquisition
by an employee benefit plan maintained by the Company or any of its subsidiaries, or (z) any acquisition which complies with Sections 6(g)(iii)(A)-(C); or 

(ii)    The Incumbent Directors cease for any reason to constitute a majority of the Board. For the
purposes hereof, “Incumbent Directors” shall mean for any period of 12 consecutive months, individuals who, at the beginning of such period, constitute the Board together with any new director(s) (other than a director designated by
a person who shall have entered into an agreement with the Company to effect a transaction described in Section 6(g)(i) or 6(g)(iii) whose election or nomination for election to the Board was approved by a vote of at least a majority (either by
a specific vote or by approval of the proxy statement of the Company in which such person is named as a nominee for director without objection to such nomination) of the directors then still in office who either were directors at the beginning of
the 12-month period or whose election or nomination for election was previously so approved. No individual initially elected or nominated as a director of the Company as a result of an actual or threatened
election contest with respect to directors or as a result of any other actual or threatened solicitation of proxies by or on behalf of any person other than the Board shall be an Incumbent Director; 

(iii)    The consummation by the Company (whether directly involving the Company or indirectly involving
the Company through one or more intermediaries) of (x) a merger, consolidation, reorganization, or business combination, (y) a sale or other disposition of all or substantially all of the Company’s assets in any single transaction or
series of related transactions or (z) the acquisition of assets or stock of another entity, in each case other than a transaction: (A) which results in the Company’s voting securities outstanding immediately before the transaction
continuing to represent (either by remaining outstanding or by being converted into voting securities of the Company or the person that, as a result of the transaction, controls, directly or indirectly, the Company or owns, directly or indirectly,
all or substantially all of the Company’s assets or otherwise succeeds to the business of the Company (the Company or such person, the “Successor Entity”)) directly or indirectly, at least a majority of the combined voting
power of the Successor Entity’s outstanding voting securities immediately after the transaction, and (B) after which no person or group beneficially owns voting securities representing 50% or more of the combined voting power of the
Successor Entity; provided, however, that no person or group shall be treated for purposes of this clause (B) as beneficially owning 50% or more of the combined voting power of the Successor Entity solely as a result of the
voting power held in the Company prior to the consummation of the transaction; and (C) after which at least a majority of the members of the board of directors (or the analogous governing body) of the Successor Entity were Board members at the
time of the Board’s approval of the execution of the initial agreement providing for such transaction; or 

  
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 (iv)    The date which is 10 business days prior to the
completion of a liquidation or dissolution of the Company. 
 Notwithstanding the foregoing, a “Change in Control” must also constitute a
“change in control event” as defined in Treasury Regulation §1.409A-3(i)(5). 

(h)    Definition of Change in Control Period. For purposes hereof, “Change in Control Period”
shall mean the period commencing three months prior to a Change in Control and ending on the eighteen (18)-month anniversary of the Change in Control. 

(i)    Definition of Good Reason. For purposes hereof, “Good Reason” shall mean any one of the
following: (i) the material reduction of Executive’s base compensation or bonus target, (ii) the material reduction of Executive’s duties and responsibilities as set forth herein (including material reduction in status, material
reduction in offices and/or a requirement to report to any person or entity other than the CEO of the Company, or following a Change in Control, the ultimate parent company of the surviving entity in such Change in Control that has at least one
class of publicly traded securities listed on a national stock exchange ) (iii) the Company’s material breach of this Agreement, or (iv) the relocation of Executive’s principal place of employment that increases Executive’s one-way commute by more than thirty-five (35) miles, provided, that, in each case, Executive will not be deemed to have Good Reason unless (i) Executive first provides the CEO with written notice of
the condition giving rise to Good Reason within thirty (30) days of its initial occurrence, (ii) the Company or the successor company fails to cure such condition within thirty (30) days after receiving such written notice (the
“Cure Period”), and (iii) Executive’s resignation based on such Good Reason is effective within thirty (30) days after the expiration of the Cure Period. 

(j)    Definition of Involuntary Termination. For purposes hereof, “Involuntary Termination” shall mean
Executive’s termination (A) by the Company without Cause, (B) by Executive for Good Reason, (C) due to death or (D) due to permanent and total disability within the meaning of Section 22(e) of the Code (a
“Disability”). 
 7.    Assignment and Successors. The Company shall assign its
rights and obligations under this Agreement to any successor to all or substantially all of the business or the assets of the Company (by merger or otherwise). This Agreement shall be binding upon and inure to the benefit of the Company, Executive,
and their respective successors, assigns, personnel, and legal representatives, executors, administrators, heirs, distributees, devisees, and legatees, as applicable. None of Executive’s rights or obligations may be assigned or transferred by
Executive, other than Executive’s rights to payments hereunder, which may be transferred only by will, operation of law, or as otherwise provided herein. 

8.    Miscellaneous Provisions. 

(a)    Confidentiality Agreement. Executive agrees to execute the Company’s standard form proprietary
information and inventions assignment agreement, effective as of the Effective Date. 
 (b)    Non-Solicitation of Employees. For a period of one (1) year following Executive’s Date of Termination, Executive shall not, either directly or indirectly (i) solicit for

  
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employment by any individual, corporation, firm, or other business, any employees, consultants, independent contractors, or other service providers of the Company or any of its affiliates, or
(ii) solicit any employee or consultant of the Company or any of its affiliates to leave the employment or consulting of or cease providing services to the Company or any of its affiliates; provided, however, that the foregoing
clauses (i) and (ii) shall not apply to inbound inquiries or any general advertisement or solicitation (or any hiring pursuant to such advertisement or solicitation) that is not specifically targeted to such employees or consultants.
Notwithstanding the foregoing, the preceding sentence shall not apply in the event Executive experiences an Involuntary Termination during or after a Change in Control Period. 

(c)    Governing Law. This Agreement shall be governed, construed, interpreted, and enforced in accordance with its
express terms, and otherwise in accordance with the substantive laws of the State of California, without giving effect to any principles of conflicts of law, whether of the State of California or any other jurisdiction, and where applicable, the
laws of the United States, that would result in the application of the laws of any other jurisdiction. 

(d)    Validity. The invalidity or unenforceability of any provision or provisions of this Agreement shall not
affect the validity or enforceability of any other provision of this Agreement, which shall remain in full force and effect. 

(e)    Counterparts. This Agreement may be executed in several counterparts, each of which shall be deemed to be an
original, but all of which together will constitute one and the same Agreement. Signatures delivered by facsimile shall be deemed effective for all purposes. 

(f)    Entire Agreement. The terms of this Agreement are intended by the Parties to be the final expression of their
agreement with respect to the employment of Executive by the Company and supersede all prior understandings and agreements, whether written or oral, regarding Executive’s service to the Company, including without limitation, the Prior
Agreement. The Parties further intend that this Agreement shall constitute the complete and exclusive statement of their terms and that no extrinsic evidence whatsoever may be introduced in any judicial, administrative, or other legal proceeding to
vary the terms of this Agreement. 
 (g)    Amendments; Waivers. This Agreement may not be modified, amended, or
terminated except by an instrument in writing signed by Executive and a duly authorized representative of the Company. By an instrument in writing similarly executed, Executive or a duly authorized officer of the Company, as applicable, may waive
compliance by the other Party with any specifically identified provision of this Agreement that such other Party was or is obligated to comply with or perform; provided, however, that such waiver shall not operate as a waiver of, or
estoppel with respect to, any other or subsequent failure. No failure to exercise and no delay in exercising any right, remedy, or power hereunder shall preclude any other or further exercise of any other right, remedy, or power provided herein or
by law or in equity. 
 (h)    Dispute Resolution. Executive agrees that if any disputes should arise between
Executive and the Company (including claims against its employees, officers, directors, shareholders, agents, successors, and assigns) relating or pertaining to or arising out of Executive’s employment with the Company, the dispute will be
submitted exclusively to binding arbitration before a neutral arbitrator mutually selected by the Company and Executive. This means that 

  
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disputes will be decided by an arbitrator rather than a court or jury, and that both Executive and the Company waive their respective rights to a court or jury trial. Judgment on the
arbitration award may be entered in any court having jurisdiction. Nothing herein shall prevent either Party from pursuing injunctive relief in court (without having to post a bond) to avoid irreparable harm pending completion of any arbitration.
Within twenty (20) days of the conclusion of the arbitration hearing, the arbitrator shall prepare written findings of fact and conclusions of law. Each party shall bear its own costs and attorneys’ fees in connection with arbitration;
provided that the Company shall pay all costs unique to arbitration, including the arbitrator’s fees and costs, that Executive would not be required to pay if the claim was in court. Executive shall be entitled to recover reasonable
attorneys’ fees and costs incurred by Executive in any arbitration Executive initiates to enforce Executive’s rights under this Agreement and in which Executive is deemed to be the prevailing party. 

(i)    Enforcement. If any provision of this Agreement is held to be illegal, invalid, or unenforceable under
present or future laws, such provision shall be fully severable; this Agreement shall be construed and enforced as if such illegal, invalid, or unenforceable provision had never comprised a portion of this Agreement; and the remaining provisions of
this Agreement shall remain in full force and effect and shall not be affected by the illegal, invalid, or unenforceable provision or by its severance from this Agreement. Furthermore, in lieu of such illegal, invalid, or unenforceable provision
there shall be added automatically as part of this Agreement a provision as similar in terms to such illegal, invalid, or unenforceable provision as may be possible and be legal, valid, and enforceable. 

(j)    Withholding. The Company shall be entitled to withhold from any amounts payable under this Agreement any
federal, state, local, or foreign withholding or other taxes or charges which the Company is required to withhold. The Company shall be entitled to rely on an opinion of counsel if any questions as to the amount or requirement of withholding shall
arise. 
 9.    Prior Employment. Executive represents and warrants that Executive’s
acceptance of employment with the Company has not breached, and the performance of Executive’s duties hereunder will not breach, any duty owed by Executive to any prior employer or other person. Executive further represents and warrants to the
Company that (a) the performance of Executive’s obligations hereunder will not violate any agreement between Executive and any other person, firm, organization, or other entity; (b) Executive is not bound by the terms of any agreement
with any previous employer or other party to refrain from competing, directly or indirectly, with the business of such previous employer or other party that would be violated by Executive entering into this Agreement and/or providing services to the
Company pursuant to the terms of this Agreement; and (c) Executive’s performance of Executive’s duties under this Agreement will not require Executive to, and Executive shall not, rely on in the performance of Executive’s duties
or disclose to the Company or any other person or entity or induce the Company in any way to use or rely on any trade secret or other confidential or proprietary information or material belonging to any previous employer of Executive. 

10.    Golden Parachute Excise Tax. 

(a)    Best Pay. Any provision of this Agreement to the contrary notwithstanding, if any payment or benefit
Executive would receive from the Company pursuant to this Agreement 

  
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or otherwise (“Payment”) would (i) constitute a “parachute payment” within the meaning of Section 280G of the Code and (ii) but for this sentence, be
subject to the excise tax imposed by Section 4999 of the Code (the “Excise Tax”), then such Payment will be equal to the Reduced Amount (as defined below). The “Reduced Amount” will be either (A) the
largest portion of the Payment that would result in no portion of the Payment (after reduction) being subject to the Excise Tax or (B) the entire Payment, whichever amount after taking into account all applicable federal, state, and local
employment taxes, income taxes, and the Excise Tax (all computed at the highest applicable marginal rate, net of the maximum reduction in federal income taxes which could be obtained from a deduction of such state and local taxes), results in
Executive’ s receipt, on an after-tax basis, of the greater economic benefit notwithstanding that all or some portion of the Payment may be subject to the Excise Tax. If a reduction in a Payment is
required pursuant to the preceding sentence and the Reduced Amount is determined pursuant to clause (A) of the preceding sentence, the reduction shall occur in the manner (the “Reduction Method”) that results in the greatest
economic benefit for Executive. If more than one method of reduction will result in the same economic benefit, the items so reduced will be reduced pro rata (the “Pro Rata Reduction Method”). Notwithstanding the foregoing, if the
Reduction Method or the Pro Rata Reduction Method would result in any portion of the Payment being subject to taxes pursuant to Section 409A (as defined below) that would not otherwise be subject to taxes pursuant to Section 409A, then the
Reduction Method and/or the Pro Rata Reduction Method, as the case may be, shall be modified so as to avoid the imposition of taxes pursuant to Section 409A as follows: (1) as a first priority, the modification shall preserve to the
greatest extent possible, the greatest economic benefit for Executive as determined on an after-tax basis; (2) as a second priority, Payments that are contingent on future events (e.g., being
terminated without cause), shall be reduced (or eliminated) before Payments that are not contingent on future events; and (3) as a third priority, Payments that are “deferred compensation” within the meaning of Section 409A shall
be reduced (or eliminated) before Payments that are not deferred compensation within the meaning of Section 409A. 

(b)    Accounting Firm. The accounting firm engaged by the Company for general tax purposes as of the day
prior to the Change of Control will perform the calculations set forth in Section 10(a) above. If the firm so engaged by the Company is serving as the accountant or auditor for the acquiring company, the Company will appoint a nationally
recognized accounting firm to make the determinations required hereunder. The Company will bear all expenses with respect to the determinations by such firm required to be made hereunder. The accounting firm engaged to make the determinations
hereunder will provide its calculations, together with detailed supporting documentation, to the Company within thirty (30) days before the consummation of a Change of Control (if requested at that time by the Company) or such other time as
requested by the Company. If the accounting firm determines that no Excise Tax is payable with respect to a Payment, either before or after the application of the Reduced Amount, it will furnish the Company with documentation reasonably acceptable
to the Company that no Excise Tax will be imposed with respect to such Payment. Any good faith determinations of the accounting firm made hereunder will be final, binding and conclusive upon the Company and Executive. 

11.    Section 409A. 

(a)    General. The intent of the Parties is that the payments and benefits under this Agreement comply with or be
exempt from Section 409A of the Code and the Department of 

  
 11 

 
Treasury regulations and other interpretive guidance issued thereunder, including without limitation any such regulations or other guidance that may be issued after the Effective Date,
(“Section 409A”) and, accordingly, to the maximum extent permitted, this Agreement shall be interpreted to be in compliance therewith. If Executive notifies the Company that Executive has received advice of tax
counsel of a national reputation with expertise in Section 409A that any provision of this Agreement would cause Executive to incur any additional tax or interest under Section 409A (with specificity as to the reason therefor) or the
Company independently makes such determination, the Company and Executive shall take commercially reasonable efforts to reform such provision to try to comply with or be exempt from Section 409A through good faith modifications to the minimum
extent reasonably appropriate to conform with Section 409A, provided that any such modifications shall not increase the cost or liability to the Company. To the extent that any provision hereof is modified in order to comply with or be
exempt from Section 409A, such modification shall be made in good faith and shall, to the maximum extent reasonably possible, maintain the original intent and economic benefit to Executive and the Company of the applicable provision without
violating the provisions of Section 409A. 
 (b)    Separation from Service. Notwithstanding any
provision to the contrary in this Agreement: (i) no amount that constitutes “deferred compensation” under Section 409A shall be payable pursuant to Section 6(b) or Section 6(c) above unless the termination of
Executive’s employment constitutes a “separation from service” within the meaning of Section 1.409A-1(h) of the Department of Treasury Regulations (“Separation from
Service”); (ii) for purposes of Section 409A, Executive’s right to receive installment payments shall be treated as a right to receive a series of separate and distinct payments; and (iii) to the extent that any reimbursement
of expenses or in-kind benefits constitutes “deferred compensation” under Section 409A, such reimbursement or benefit shall be provided no later than December 31st of the year following the year in which the expense was incurred. The amount of expenses reimbursed in one year shall not affect the amount eligible for reimbursement in any subsequent year. The
amount of any in-kind benefits provided in one year shall not affect the amount of in-kind benefits provided in any other year. 

(c)    Specified Employee. Notwithstanding anything in this Agreement to the contrary, if Executive is deemed by the
Company at the time of Executive’s Separation from Service to be a “specified employee” for purposes of Section 409A, to the extent delayed commencement of any portion of the benefits to which Executive is entitled under this
Agreement is required in order to avoid a prohibited distribution under Section 409A, such portion of Executive’s benefits shall not be provided to Executive prior to the earlier of (i) the expiration of the six (6)-month period
measured from the date of Executive’s Separation from Service with the Company or (ii) the date of Executive’s death. Upon the first business day following the expiration of the applicable Section 409A period, all payments
deferred pursuant to the preceding sentence shall be paid in a lump sum to Executive (or Executive’s estate or beneficiaries), and any remaining payments due to Executive under this Agreement shall be paid as otherwise provided herein. 

(d)    Release. Notwithstanding anything to the contrary in this Agreement, to the extent that any payments due
under this Agreement as a result of Executive’s termination of employment are subject to Executive’s execution and delivery of a Release, (i) the Company shall deliver the Release to Executive within ten (10) business days
following Executive’s Date of Termination, and the Company’s failure to deliver a Release prior to the expiration of such ten (10) business day period shall constitute a waiver of any requirement to execute a Release,
(ii) if 

  
 12 

 
Executive fails to execute the Release on or prior to the Release Expiration Date (as defined below) or timely revokes Executive’s acceptance of the Release thereafter, Executive shall not
be entitled to any payments or benefits otherwise conditioned on the Release, and (iii) in any case where Executive’s Date of Termination and the Release Expiration Date fall in two separate taxable years, any payments required to be made
to Executive that are conditioned on the Release and are treated as nonqualified deferred compensation for purposes of Section 409A shall be made in the later taxable year. For purposes of this Section 11(d), “Release Expiration
Date” shall mean the date that is twenty-one (21) days following the date upon which the Company timely delivers the Release to Executive, or, in the event that Executive’s termination of
employment is “in connection with an exit incentive or other employment termination program” (as such phrase is defined in the Age Discrimination in Employment Act of 1967), the date that is forty-five (45) days following such
delivery date. To the extent that any payments of nonqualified deferred compensation (within the meaning of Section 409A) due under this Agreement as a result of Executive’s termination of employment are delayed pursuant to this
Section 11(d), such amounts shall be paid in a lump sum on the first payroll date following the date that Executive executes and does not revoke the Release (and the applicable revocation period has expired) or, in the case of any payments
subject to Section 11(d)(iii), on the first payroll period to occur in the subsequent taxable year, if later. 

12.    Employee Acknowledgement. Executive acknowledges that Executive has read and understands this
Agreement, is fully aware of its legal effect, has not acted in reliance upon any representations or promises made by the Company other than those contained in writing herein, and has entered into this Agreement freely based on Executive’s own
judgment. 
 [Signature Page Follows] 

  
 13 

 IN WITNESS WHEREOF, the Parties have duly executed this Agreement as of the date and year
first above written. 
  

			
	SIENNA BIOPHARMACEUTICALS, INC.
		
	By:	 	/s/ Frederick C. Beddingfield III
	Frederick C. Beddingfield III, MD, PhD
	President and Chief Executive Officer
	
	Date: March 21, 2019
	
	EXECUTIVE
		
	By:	 	/s/ Alexander Azoy
	Alexander Azoy
	
	Date: March 21, 2019
	
	Address:EX-10.3

 Exhibit 10.3 

SEPARATION AND GENERAL RELEASE AGREEMENT 

I, John W. Smither, enter into this Separation and General Release Agreement (“Agreement”) with Sienna Biopharmaceuticals,
Inc., a Delaware Corporation (the “Company”), as of the Effective Date, which is the eighth (8th) day after the date on which I sign this Agreement. 

WHEREAS, I am employed by the Company pursuant to that certain Employment Agreement effective as of April 16, 2018 (the
“Employment Agreement”); 
 WHEREAS, the Company and I (collectively the “Parties”, or, individually, a
“Party”) desire to specify the terms and date of my resignation from the Company and resolve any and all disputes that may exist between us and to specify the terms of my resignation; and 

NOW, THEREFORE, in consideration of the mutual promises made herein and for other good and valuable consideration, the receipt and adequacy of
which are hereby acknowledged, the Parties hereby agree as follows: 
 1.    Resignation from Employment.  

(a)    I hereby tender my resignation as an officer and employee of the Company and any of its parents, subsidiaries and
affiliates (the “Affiliates”) as of April 1, 2019 (the “Resignation Date”). I agree to sign any documentation of my resignation reasonably required by the Company. 

(b)    I acknowledge and agree that, on the Resignation Date, the Company will pay me any accrued salary previously unpaid,
including my accrued, unused vacation pay, earned through the Resignation Date, subject to standard payroll deductions and withholdings. I acknowledge that I am entitled to these payments regardless of whether I execute this Agreement. 

(c)    Except as set forth in this Agreement, I understand that I am giving up any right or claim to future employment at
the Company, including without limitation, any future compensation or benefits, except as set forth in this Agreement. 

(d)    I understand and agree that I am not and will not be entitled to any payment pursuant to Sections 6(b) or
(c) of the Employment Agreement. 
 (e)    I have submitted any unreimbursed business expenses on or before the
Resignation Date, which will be reimbursed in accordance with Company policy, and I have not incurred any business expenses after the date this Agreement was presented to me without express written approval of the Company. I acknowledge that I am
entitled to these reimbursements regardless of whether I execute this Agreement. 
 (f)    On or before the Resignation
Date, I will return to the Company all property of the Company, including without limitation, documents and records, all keys, access cards, credit cards, calling cards, computer hardware and software, cellular phones and other mobile communications
devices. 
 (g)    Subject to Section 11 below, I hereby reaffirm the covenants, terms and conditions set forth in
the Employee Proprietary Information and Inventions Assignment Agreement between the Company and me dated as of April 19, 2018 (the “Confidentiality Agreement”) and acknowledge that the Confidentiality Agreement shall survive
termination of my employment and remain in full force and effect in accordance with its terms, including, without limitation, the confidentiality information and non-solicitation restrictive covenants set
forth therein. 

  
 1 

 (h)    Subject to Section 11, I will cooperate fully with the
Company and its Affiliates concerning reasonable requests for information about the business of the Company or its Affiliates or my involvement and participation therein; the defense or prosecution of any claims or actions now in existence or which
may be brought in the future against or on behalf of the Company or its subsidiaries or affiliates which relate to events or occurrences that transpired while I was employed by the Company; and in connection with any investigation or review by any
federal, state or local regulatory, quasi- or self-regulatory or self-governing authority or organization (including, without limitation, the Securities and Exchange Commission and the Financial Industry Regulatory Authority, Inc.) as any such
investigation or review relates to events or occurrences that transpired while I was employed by the Company. I agree that, upon reasonable request and taking into account my other obligations, to be available to meet and speak with officers or
employees of the Company, its Affiliates and/or their counsel at reasonable times and locations, executing accurate and truthful documents, appearing at the Company’s request as a witness at depositions, trials or other proceedings without the
necessity of a subpoena, and taking such other actions as may reasonably be requested by the Company and/or its counsel to effectuate the foregoing. The Company will reimburse me for reasonable expenses incurred by me in response to Company requests
pursuant to this Section 1(f). 
 (i) I acknowledge that the payment and arrangements herein shall constitute full and complete
satisfaction of any and all amounts properly due and owing to me as a result of my employment with the Company and the termination thereof. I further acknowledge that, other than the Confidentiality Agreement and the agreements evidencing my
outstanding equity awards (as amended by Section 3 below), this Agreement shall supersede each agreement entered into between Executive and the Company regarding Executive’s employment, including, without limitation, that the Employment
Agreement. Each such agreement superseded hereby shall be deemed terminated and of no further effect as of the Resignation Date. 

2.    COBRA Benefits. Subject my timely execution and non-revocation of
this Agreement and my continued compliance with the terms and conditions set forth in Sections 1 and 4 of this Agreement, provided that I timely elect to continue my healthcare insurance benefits under the provisions of the Consolidated Omnibus
Budget Reconciliation Act of 1985, as amended (“COBRA”), the Company will pay the cost of monthly COBRA premiums for my and my covered dependents, if any, continued healthcare coverage under the Company’s group health plans for
coverage during the period beginning on the Resignaiton Date and ending on the earlier of (i) the three-month anniversary of the Resignation Date or (ii) the date I become eligible for comparable coverage under another employer’s
group health plan(s), provided, however, that if (1) any plan pursuant to which such benefits are provided is not, or ceases prior to the expiration of the continuation coverage period to be, exempt from the application of
Section 409A of the Internal Revenue Code of 1986, as amended, under Treasury Regulation Section 1.409A-1(a)(5), (2) the Company is otherwise unable to continue to cover me under its group health
plans, or (3) the Company cannot provide the benefit without violating applicable law (including, without limitation, Section 2716 of the Public Health Service Act), then, in any such case, an amount equal to each remaining premium shall
thereafter be paid to me in substantially equal monthly installments over the remaining period the Company would otherwise pay the premiums. If I become eligible for healthcare insurance benefits from any other employer, I will promptly notify the
Company, and I understand that the Company shall not be obligated to continue to pay my COBRA premiums thereafter. After the Company ceases to pay premiums pursuant to the preceding sentence, I may, if eligible, elect to continue healthcare coverage
at my expense in accordance with the provisions of COBRA. I acknowledge that I am solely responsible for all matters relating to my continuation of coverage pursuant to COBRA, including, without limitation, my election of such coverage and your
timely payment of premiums. I agree that the benefits provided by this Section 2 are not required under the Company’s normal policies and procedures and are provided as a severance solely in connection with this Agreement. I acknowledge
and agree that the benefits referenced in this Section 2 constitute adequate and valuable consideration, in and of themselves, for the promises contained in this Agreement. 

  
 2 

 3.    Equity Awards. I understand that, as of my Resignation
Date, I forfeited any right in any unvested shares subject to my outstanding equity awards. With regard to that certain option to purchase 14,422 shares of common stock of the Company granted to me on January 1, 2019 (the “Bonus
Option”), the post-termination exercise period applicable to the vested portion of the Bonus Option shall be extended through the earlier of (A) the third anniversary of the Separation Date or (B) the original expiration date of
the Bonus Date, subject to earlier termination upon certain event as provided in the Company’s equity plan (such date, the “Extension Date”), and the agreements evidencing the Bonus Option shall be deemed amended to the extent
necessary to reflect such extended exercisability. If I desire to exercise any vested shares subject to my equity awards, I must follow the procedures set forth in my applicable award agreement, including payment of the exercise price and any
withholding obligations. If by the Extension Date for the Bonus Option or the applicable date set forth in any other award agreement for options, the Company has not received a duly executed notice of exercise and remuneration in accordance with my
applicable option agreement, my vested shares subject to the options shall automatically terminate and be of no further effect. 

4.    Non-Disparagement/References. 

(a)    Subject to Section 11, the Parties agree that to the extent the Company or its Affiliates communicate to my
coworkers, other than officers of the Company or its Affiliates, or to third parties, the Company, consistent with this Agreement, will characterize my separation as a resignation from the Company to pursue other interests and that I will consult
with the Company during a transition period. 
 (b)    Subject to Section 11, from the date I sign this Agreement
forward, I will not, publicly or privately, disparage, defame or criticize the Company, its Affiliates, officers, directors, products, services, technology, partners, agents, business or shareholders. 

(c)    Subject to Section 11, the Company will instruct the Executive Officers of the Company not to, publicly or
privately, disparage, defame or criticize me. The Company shall be responsible for their statements so long as they remain employed by the Company. 

(d)    Nothing contained in this Section 4 or this Agreement shall be interpreted to require any Party to make any
false statement, or restrict any Party in any way from providing any information required by applicable law or legal process. 
 5.
    Release of Claims by Employee. 
 (a)    General Release. I, on behalf of myself,
my heirs, estate, trust(s), successors and assigns, hereby release and forever discharge the “Releasees” hereunder, consisting of the Company and the Affiliate, and each of their respective partners, members, managers, associates,
affiliates, subsidiaries, successors, heirs, assigns, agents, directors, officers, employees, shareholders, representatives, lawyers, insurers, and all persons acting by, through, under or in concert with them, or any of them, of and from any and
all Claims, as defined in Section 5(b).
 (b)    Claims Released. The “Claims” released
herein include any and all manner of complaints, claims, inquiries, action or actions, cause or causes of action, in law or in equity, suits, debts, liens, contracts, agreements, promises, liability, claims, demands, damages, losses, costs,
attorneys’ fees or expenses, of any nature whatsoever, known or unknown, fixed or contingent, which I now has have or may hereafter have against the Releasees, or any of them, by reason of any matter, cause, or thing whatsoever

  
 3 

 
from the beginning of time to the date hereof. Without limiting the generality of the foregoing, Claims shall include: any claims in any way arising out of, based upon, or related to my
employment by or service as a director to any of the Releasees, or any of them, or the termination thereof; any claim for wages, salary, commissions, bonuses, fees, incentive payments, profit-sharing payments, expense reimbursements, leave
(including annual leave, long service leave and personal leave), vacation redundancy or separation pay, notice of termination or payment in lieu of notice or other benefits; any alleged breach of any express or implied contract of employment,
including without limitation the Employment Agreement and the Letter; any alleged torts or other alleged legal restrictions on the Company’s rights to terminate my employment; and any alleged violation of any federal, state or local statute or
ordinance regulation, award enterprise agreement or other instrument made or approved under any law, including, without limitation, Claims arising under: Age Discrimination in Employment Act, as amended, 29 U.S.C. § 621, et
seq. (the “ADEA”); Title VII of the Civil Rights Act of 1964, as amended by the Civil Rights Act of 1991, 42 U.S.C. § 2000 et seq.; Equal Pay Act, as amended, 29 U.S.C. § 206(d); the Civil Rights Act of
1866, 42 U.S.C. § 1981; the Family and Medical Leave Act of 1993, 29 U.S.C. § 2601 et seq.; the Americans with Disabilities Act of 1990, 42 U.S.C. § 12101 et seq.; the False Claims Act , 31 U.S.C. § 3729 et
seq.; the Employee Retirement Income Security Act, as amended, 29 U.S.C. § 1001 et seq.; the Worker Adjustment and Retraining Notification Act, as amended, 29 U.S.C. § 2101 et seq. the Fair Labor
Standards Act, 29 U.S.C. § 215 et seq.; the California Fair Employment and Housing Act, as amended, Cal. Lab. Code § 12940 et seq.; the California Equal Pay Law, as amended, Cal. Lab. Code §§
1197.5(a),1199.5; the Moore-Brown-Roberti Family Rights Act of 1991, as amended, Cal. Gov’t Code §§12945.2, 19702.3; California Labor Code; the California WARN Act, Cal. Lab. Code § 1400 et seq.; the California False
Claims Act, Cal. Gov’t Code § 12650 et seq.; the California Corporate Criminal Liability Act, Cal. Penal Code § 387; or under the California Labor Code), or any other federal, state or local law. 

(c)    Claims not Released. Nothing in this Agreement is intended to release or waive my rights (i) under
COBRA, (ii) to unemployment insurance benefits, (iii) to any accrued and vested pension benefits, stock options, restricted shares or other benefits under any employee plan in which I was a participant prior to the Resignation Date,
(iv) to commence an action or proceeding to enforce the terms of this Agreement, (v) to indemnification for attorneys’ fees, costs, and/or expenses pursuant to applicable statutes, Certificates of Incorporation and By-laws of the Company or the Affiliates, including any rights under California Labor Code Sections 2800 or 2802 (the “Unreleased Claims”); or (vi) any right that may not be released by private
agreement. 
 (d)    Unknown Claims. I ACKNOWLEDGE THAT I AM HEREBY ADVISED OF AND FAMILIAR WITH THE PROVISIONS OF
CALIFORNIA CIVIL CODE SECTION 1542, WHICH PROVIDES AS FOLLOWS: 
 “A GENERAL RELEASE DOES NOT EXTEND TO CLAIMS WHICH
THE CREDITOR OR RELEASING PARTY DOES NOT KNOW OR SUSPECT TO EXIST IN HIS OR HER FAVOR AT THE TIME OF EXECUTING THE RELEASE AND THAT, IF KNOWN BY HIM OR HER, WOULD HAVE MATERIALLY AFFECTED HIS OR HER SETTLEMENT WITH THE DEBTOR OR RELEASED
PARTY.” 
 BEING AWARE OF SAID CODE SECTION, I HEREBY EXPRESSLY WAIVE ANY RIGHTS THAT I MAY HAVE THEREUNDER, AS WELL AS UNDER ANY OTHER STATUTES OR
COMMON LAW PRINCIPLES OF SIMILAR EFFECT. 

  
 4 

 (e)    Review and Revocation  

(i)    I understand that under the Older Workers Benefit Protection Act, I have a right to review and revoke this
agreement as follows. I agree and acknowledge that this Agreement includes a waiver and release of all claims that I have or may have under the ADEA. The following terms and conditions apply to and are part of the waiver and release of the ADEA
claims under this general release: 
 (A)    This Agreement is written in a manner calculated to be
understood by me, and I understand it. 
 (B)    The waiver and release of claims under the ADEA
contained in this Agreement does not cover rights or claims that may arise after the date on which I sign this Agreement. 

(C)    This Agreement provides for consideration in addition to anything of value to which I am already
entitled. 
 (D)    I am hereby advised to consult an attorney before signing this Agreement. 

(E)    I have been granted twenty-one (21) days after
receiving this Agreement to decide whether or not to sign this Agreement. If I sign this Agreement prior to the expiration of the twenty-one (21) day period, I do so voluntarily and after having had the
opportunity to consult with an attorney, and I hereby waive the remainder of the twenty-one (21) day period. I agree that any changes or amendments to this Agreement, whether or not material, shall not
restart the twenty-one (21) day period. 
 (F)    I have the
right to revoke this Agreement within seven (7) days of signing this Agreement. Consequently, this Agreement shall not be enforceable or effective until the eighth (8th) day after I sign this
Agreement (the “Effective Date”). In the event this Agreement is revoked, this Agreement will be null and void in its entirety, and I will not be entitled to the separation benefits as provided in Section 2. 

(G)    If I wish to revoke this Agreement, I must deliver written notice stating my intent to revoke this
Agreement to the person and address specified in Section 6, on or before 5:00 p.m. on the seventh (7th) Day after the date on which I signed this Agreement. 

(f)    No Assignments of Claims. I represent and warrant that there has been no assignment or other transfer of any
interest in any Claim that I may have against Releasees, or any of them, and I agrees to indemnify and hold Releasees, and each of them, harmless from any liability, Claims, demands, damages, costs, expenses and attorneys’ fees incurred by
Releasees, or any of them, as the result of any such assignment or transfer or any rights or Claims under any such assignment or transfer. It is the intention of the Parties that this indemnity does not require payment as a condition precedent
to recovery by the Releasees against me under this indemnity. 
 (g)    No Actions. I agree that if I hereafter
commence any suit arising out of, based upon, or relating to any of the Claims released hereunder or in any manner asserts against Releasees, or any of them, any of the Claims released hereunder, then I will pay to Releasees, and each of them, in
addition to any other damages caused to Releasees thereby, all attorneys’ fees incurred by Releasees in defending or otherwise responding to said suit or Claim. The foregoing shall not apply to: (1) my right to file a charge with the
United States Equal Employment Opportunity Commission; however, I hereby waive any right to any damages or individual relief resulting from any charge; or (2) any suit or Claim to the extent it challenges the effectiveness of this release with
respect to a claim under the Age Discrimination in Employment Act. 

  
 5 

 (h)    No Admission. I understand and agree that neither the
payment of any sum of money nor the execution of this Agreement shall constitute or be construed as an admission of any liability whatsoever by the Releasees, or any of them, who have consistently taken the position that they have no liability
whatsoever to me. 
 (i)    My Representations. I warrant and represent that (i) I have not filed or
authorized the filing of any complaints, charges or lawsuits against the Company, or any affiliate of the Company with any governmental agency or court, and that if, unbeknownst to me, such a complaint, charge or lawsuit has been filed on my behalf,
I will immediately cause it to be withdrawn and dismissed, (ii) I have reported all hours worked as of the Resignation Date and have been paid all compensation, wages, bonuses, commissions, and/or benefits to which I may be entitled and no
other compensation, wages, bonuses, commissions and/or benefits are due to me, except as provided in this Agreement, (iii) I have no known workplace injuries or occupational diseases and have been provided and/or have not been denied any leave
requested under the Family and Medical Leave Act or any similar state law, (iv) the execution, delivery and performance of this Agreement by me does not and will not conflict with, breach, violate or cause a default under any agreement,
contract or instrument to which I am a party or any judgment, order or decree to which I am subject, and (v) upon the execution and delivery of this Agreement by the Company and me, this Agreement will be a valid and binding obligation of me
and Company, enforceable in accordance with its terms. 
 (j)    No Reliance. I acknowledge that different or
additional facts may be discovered in addition to what is now known or believed to be true by me with respect to the matters released in this Agreement, and I agree that this Agreement shall be and remain in effect in all respects as a complete and
final release of the matters released, notwithstanding any different or additional facts. 
 6.    Notices. 

Any notice to be given hereunder shall be deemed sufficient if addressed in writing and delivered by certified mail to the addresses listed
below: 
 If to the Company: 

Sienna Biopharmaceuticals, Inc. 

30699 Russell Ranch Road 
 Suite
140 
 Westlake Village, CA 91362 

Attn: General Counsel 
 If to me,
to: 
 John W. Smither 
 3355
Hampton Court 
 Westlake Village, CA 91362 

Notices and communications shall be effective when actually received by the addressee. Either Party may change the address for notice by
sending written notice of a change of address to the other Party in accordance with this Section 6. 

  
 6 

 7.    Severability. If any term, provision, covenant or condition
of this Agreement is held by a court of competent jurisdiction to exceed the limitations permitted by applicable law, as determined by such court in such action, then the provisions will be deemed reformed to apply to the maximum limitations
permitted by applicable law and the Parties hereby expressly acknowledge their desire that in such event such action be taken. Notwithstanding the foregoing, the Parties further agree that if any term, provision, covenant or condition of this
Agreement is held by a court of competent jurisdiction to be invalid, void or unenforceable, the remainder of the provisions shall remain in full force and effect and in no way shall be affected, impaired or invalidated. 

8.    Entire Agreement; Amendment. This Agreement represents the entire agreement and understanding among the
Parties concerning my employment and separation from the Company and, except as expressly set forth herein or under the Confidentiality Agreement, supersedes and replaces any and all prior agreements and understandings concerning my relationship
with the Company and his compensation from the Company. This Agreement may only be amended by a writing signed by both me and a duly authorized officer of the Company. I further understand that the Employment Agreement is hereby terminated, except
that Sections 8(a), (b) and (h) of the Employment Agreement shall survive the termination of the Employment Agreement. Notwithstanding the foregoing, my obligations under any restrictive covenant, confidentiality, intellectual property and/ or
assignment of inventions agreement or provisions of any agreement, including without limitation, the Confidentiality Agreement, shall survive the Resignation Date and shall not be amended, limited or superseded by this Agreement. 

9.    Governing Law. This Agreement shall be governed by the laws of the State of California without regard to its
conflict of laws rules. 
 10.    Confidentiality. Subject to Section 11, I will not, directly or
indirectly, provide to any person or entity any information that concerns or relates to the negotiation of or circumstances leading to the execution of this Agreement or to the terms and conditions hereof, provided that I may make disclosure of the
foregoing: (a) to the extent that such disclosure is specifically required by law or legal process or as authorized in writing by the Company; (b) to my tax advisor(s) or accountant(s) as may be necessary for the preparation of tax returns
or other reports required by law; (c) to my attorney(s); (d) to members of my immediate family; and/or (e) to any tax agency. Provided, that prior to disclosing any such information (except disclosures required by law or legal process or
as authorized in writing), I must inform the recipients that they are bound by the limitations of this Section 10. 

11.    Right to Communicate Directly with Governmental or Self-Regulatory Bodies. Nothing in this Agreement, the
Confidentiality Agreement or any exhibit or attachment hereto prohibits or in any way restricts me, or any other person, from communicating directly with, cooperating with or providing information to the U.S. Securities and Exchange Commission or
any other governmental or regulatory body or any self-regulatory organization or making other disclosures that are protected under applicable law or receiving awards from or by a government agency for providing information. I understand that I do
not need the prior authorization of the Company before taking such actions and am not required to inform the Company if you do so. Furthermore, in accordance with 18 U.S.C. § 1833, notwithstanding anything to the contrary in the Confidentiality
Agreement or this Agreement: (i) I shall not be in breach of this Agreement, and shall not be held criminally or civilly liable under any federal or state trade secret law (x) for the disclosure of a trade secret that is made in confidence
to a federal, state, or local government official or to an attorney solely for the purpose of reporting or investigating a suspected violation of law, or (y) for the disclosure of a trade secret that is made in a complaint or other document
filed in a lawsuit or other proceeding, if such filing is made under seal; and (ii) if I file a lawsuit for retaliation by the Company for reporting a suspected violation of law, I may disclose the trade secret to my attorney, and may use the
trade secret information in the court proceeding, if I file any document containing the trade secret under seal, and do not disclose the trade secret, except pursuant to court order. 

  
 7 

 12.    Attorneys’ Fees. The Parties shall bear their own
attorneys’ fees and expenses in connection with the negotiation of and entry into this Agreement. In the event of any litigation or arbitration arising out of a dispute as to the interpretation, enforcement or breach of this Agreement, the
prevailing party shall be entitled to an award of its attorneys’ fees, expert witness expenses and legal costs reasonably incurred. 

13.    Voluntary Execution of Agreement. I acknowledge and agree that I am executing this Agreement voluntarily and
without any duress or undue influence on the part or behalf of the Company, with the full intent of releasing all Claims. I further acknowledge and agree that I have been represented with respect to this Agreement by legal counsel of my own choice
or I have voluntarily declined to seek such counsel. 
 [Signature Page to Follow] 

  
 8 

 IN WITNESS WHEREOF, the Parties have caused this Agreement to be to be duly executed and
delivered as of the date indicated next to their respective signatures below, which such dates shall be on or after the Resignation Date and prior to the 21st day following the Resignation Date.

  

					
	COMPANY:	 		 	Sienna Biopharmaceuticals, Inc.
			
	  
	 		 	/s/ Timothy K. Andrews
		 		 	By:    Timothy K. Andrews
		 		 	Title: General Counsel and Secretary
			
		 		 	Date: April 1, 2019
			
	EMPLOYEE:	 		 	/s/ John S. Smither
		 		 	John W. Smither
			
		 		 	Date: April 1, 2019

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