Sebaceous cyst
Synonyms and keywords: Wen; pilar cyst; Keratinizing cyst

# Overview
A sebaceous cyst (a form of trichilemmal cyst) is a closed sac or cyst below the surface of the skin that has a lining that resembles the uppermost part (infundibulum) of a hair follicle and fills with a fatty white, semi-solid material called sebum. Sebum is produced by sebaceous glands of the epidermis.

# Terminology
It is sometimes (but not always) considered to be equivalent to epidermoid cyst, or similar enough to be addressed as a single entity.
Some sources state that a "sebaceous cyst" is defined not by the contents of the cyst (sebum) but by the origin (sebaceous glands). Because a "epidermoid cyst" originates in the epidermis, and a "pilar cyst" originates from hair follicles, neither type of cyst would be considered a sebaceous cyst by this definition. However, in practice, the terms are often used interchangeably.
"True" sebaceous cysts are relatively rare.

# Presentation
The scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts, though they may occur anywhere on the body except the palms of the hands and soles of the feet. In males a common place for them to develop is the scrotum and chest .They are more common in hairier areas, where in cases of long duration they could result in hair loss on the skin surface immediately above the cyst. They are smooth to the touch, vary in size, and are generally round in shape.
They are generally mobile masses that can consist of:
- Fibrous tissues and fluids
- A fatty, (keratinous), substance that resembles cottage cheese, in which case the cyst may be called "keratin cyst"
- A somewhat viscous, serosanguinous fluid (containing purulent and bloody material)
The nature of the contents of a sebaceous cyst, and of its surrounding capsule, will be determined by whether the cyst has ever been infected.
With surgery, a cyst can usually be excised in its entirety; poor surgical technique or previous infection leading to scarring and tethering of the cyst to the surrounding tissue may lead to rupture during excision and removal. A completely removed cyst will not recur, though if the patient has a predisposition to cyst formation further cysts may develop in the same general area.

# Causes
Blocked sebaceous glands, swollen hair follicles, and excessive testosterone production will cause such cysts.
A case has been reported of a sebaceous cyst being caused by Dermatobia hominis.

# Treatment
Sebaceous cysts generally do not require medical treatment.  However, if they continue to grow, they may become unsightly, painful, infected, or all of the above.

## Surgery
Surgical excision of a sebaceous cyst is a simple procedure to completely remove the sac and its contents.  
There are three general approaches used: traditional wide excision, minimal excision, and punch biopsy excision.
The typical outpatient surgical procedure for cyst removal is to numb the area around the cyst with a local anesthetic, then to use a scalpel to open the lesion with either a single cut down the center of the swelling, or an oval cut on both sides of the centerpoint. If the cyst is small, it may be lanced instead. The person performing the surgery will squeeze out the keratin (the semi-solid material consisting principally of sebum and dead skin cells) surrounding the cyst, then use blunt-headed scissors or another instrument to hold the incision wide open while using fingers or forceps to try to remove the cyst intact. If the cyst can be removed in one piece, the "cure rate" is 100%. If, however, it is fragmented and cannot be entirely recovered, the operator may curettage (scrape) the remaining exposed fragments, then burn them with an electro-cauterization tool, in an effort to kill them in place. In such cases the cyst may or may not recur. In either case, the incision is then disinfected and, if necessary, the skin is stitched back together over it. A scar will result.
An infected cyst may require oral antibiotics or other treatment before excision.
An approach involving incision, rather than excision, has also been proposed.

## Nonsurgical
Another common and effective method of treatment involves placement of a heat-pad directly on the cyst for about fifteen minutes, twice daily, for about 10 days (depending on size and location of the cyst).
This method works by bringing the temperature of the wax-like material inside of the cyst to a temperature at which it melts and can be reabsorbed and processed by the body as a small amount of oily fluid. This method is preferred over surgery both for reasons of associated costs and risks of surgery. This methodology is not applicable for non-sebaceous cysts, however, as other varieties of cysts do not contain the same hardened sebum deposits, and therefore do not melt to be reabsorbed by the body.
Under no circumstances must one try to pop the cyst as it can lead to infection of the surrounding tissue. The neck is a vitally dangerous region due to the glands and blood vessels.
Some cysts in the genital region are forms of herpes and need to be examined by a physician.