Epidermoid Cyst (Sebaceous Cyst)
Epidermoid cysts are slow-growing, small bumps that develop beneath the skin. They are usually painless and tend to occur on the face, neck, trunk, and sometimes the genital area.
Epidermoid cysts have the following characterisitics:
- Size: They range in size from less than 1/4 inch to nearly 2 inches in diameter
- Shape and mobility: The cysts are round bumps that easily move under the skin when felt with the fingers
- Color: The cysts are usually white or yellow, though people with darker skin may have pigmented cysts
- Other: The cyst may have a central opening plugged with a blackhead. This is the remant of a hair follicle. A thick, cheese-like material can sometimes be expressed through the opening.
NOTE: Because of the risk of infection and scarring, it is recommended that you do NOT squeeze the cyst.
Other Types of Cysts
- Sebaceous cysts. Epidermoid cysts are often called "sebaceous cysts" because they appear very similar and are often treated in the same manner. However, a true sebaceous cyst is less common and arises from cells that make up the sebaceous gland instead of the cells that form the epidermis.
- Milia are small, scattered epidermoid cysts. They appear like tiny, deep-seated whiteheads that never seem to come to the surface. They're especially common on the face of infants and older individuals with significant sun damage. They can also be caused or aggravated by long-term use of oil-based creams or cosmetics.
- Pilar Cyst. A small bump that appears on the scalp may look like an epidermoid cyst, but is like to be a "pilar cyst" or "trichilemmal cyst", which usually have thicker walls and a different lining than an epidermoid cyst.
Complications of Epidermoid Cysts
- Infection. Epidermoid cysts can become infected. Signs of infection include redness, swelling and pain around the cyst. In some cases, there may be a purulent discharge.
- Inflammation. Epidermoid cysts can become tender and swollen, even if they're not infected.
- Rupture. A ruptured cyst often leads to a boil-like abscess that requires prompt treatment.
Cause of Epidermoid Cysts
The epidermis, the topmost layer of skin, is constantly growing new skin cells and shedding old cells. If these cells grow inward, they cannot shed and start to accumulate under the skin. This is most likely to occur near small hair follicles and larger oil glands (sebaceous glands) that are concentrated on the face, neck, upper back and groin. The material that accumulates within the cyst is keratin, a protein produced by the epidermal cells.
Risk Factors for Developing Epidermoid Cysts
The following risk factors increase a person's risk for developing epidermoid cysts.
- Male. Men are more likely to have epidermoid cysts.
- Acne. Epidermoid cysts are especially common in people who've had acne.
- Signifant sun exposure. Milia, seen mainly on the face, often occur in men and women with a long history of sun exposure.
- Skin injuries. Trauma to the skin increases the chances of develping an epidermoid cyst in that injured area.
Treatment of Epidermoid Cysts
Epidermoid cysts are usually not harmful and may resolve without treatment. However, treatment may be recommended in the following cases:
- The cyst is cosmetically unappealing, such as a cyst that appears on the face.
- They cyst is in a location that is frequently irritated, such as on the neck where it may rub the collar of a shirt, or on the lower back where it may rub against a belt.
- The cyst ruptures
- The cyst is painful
- The cyst becomes infected
A cyst that's inflamed, ruptured or infected may be treated with:
- Corticosteroid Injection. A cyst that is inflamed, but not uninfected, may be injected with a corticosteroid (triamcinalone) to reduce inflammation.
- Incision and drainage. In this procedure, your doctor makes a small cut in the cyst and expresses the contents. Although incision and drainage is relatively quick and easy, cysts often recur after this treatment.
- Excision. If required, the cyst can usually be easily removed by a simple operation. The surrounding skin is first 'numbed' with a local anaesthetic (lidocaine). Then, a small incision (cut) is made over the cyst. Typically, the whole cyst, including the walls, can be extracted. The wound is then stitched up with sutures that are removed after about 1-2 weeks. A small scar will result. Sometimes, after the removal of a cyst, it gradually regrows in the same site under the scar. This is unusual but, if it occurs, it can be removed again. Your doctor may recommend treatment with antibiotics, steroids, or incision and drainage and then waiting to perform excision for four to six weeks after inflammation resolves.