Epidermoid cysts are small bumps that develop just beneath the skin on your face, neck, trunk and sometimes your genital area. They are slow-growing and often painless. Although many people refer to epidermoid cysts as sebaceous cysts, true sebaceous cysts are much less common than epidermoid cysts are. Most epidermoid cysts don't cause problems or need treatment. But if they're a cosmetic concern or they rupture or become infected, they're usually surgically removed. Epidermoid cysts are almost always noncancerous, but in rare cases, they can give rise to skin cancers. Because this occurs so seldom, epidermoid cysts usually aren't biopsied unless they have unusual characteristics that suggest a more serious problem.

Complications of Sebaceous Cysts

In rare cases, epidermoid cysts can give rise to basal and squamous cell skin cancers. Because this occurs so seldom, epidermoid cysts usually aren't biopsied unless they're solid, immobile, infected or have other unusual characteristics that suggest a more serious problem. Besides cancer, other complications include:

• Inflammation. Epidermoid cysts can become tender and swollen, even if they're not infected. Inflamed cysts are difficult to remove, and your doctor is likely to postpone treating them until the inflammation subsides.
• Rupture. A ruptured cyst often leads to a boil-like abscess that requires prompt treatment.
• Infection. An epidermoid cyst can become infected spontaneously or after a rupture.
• Genital discomfort. Genital epidermoid cysts can lead to painful intercourse and urination.

Causes of Sebaceous Cysts

The surface of your skin (epidermis) is made up of an extremely thin, protective layer of cells that your body continuously sheds. Most epidermoid cysts form when these surface cells, instead of exfoliating normally, move deeper into your skin and multiply. Most often, this occurs in areas where there are small hair follicles and larger oil glands (sebaceous glands), such as your face, neck, upper back and groin. The epidermal cells form the walls of the cyst, and then secrete the protein keratin into the interior. The keratin is the thick yellow substance that sometimes drains from the cyst.

Several factors can lead to this abnormal proliferation of cells, including:

• Damage to a hair follicle. Each hair grows from a follicle, a small pocket of modified skin in the dermis, the layer of skin just below the epidermis. Follicles damaged by injuries, such as abrasions or surgical wounds, can become blocked by surface cells.
• A ruptured sebaceous gland. Located just above the hair follicles, sebaceous glands produce sebum, the oil that lubricates your skin and coats each hair shaft. These glands are easily ruptured by inflammatory skin conditions, especially acne, making them a likely site for epidermoid cysts.
• Developmental defect. Epidermoid cysts can begin in a developing fetus when stem cells intended to form skin; hair or nails become trapped in cells forming other tissues.
• Heredity. Epidermoid cysts can develop in people with Gardner's syndrome, a rare genetic disorder that causes growths in the colon, or basal cell nevus syndrome, an inherited disease that leads to several serious defects.

Signs & Symptoms of Sebaceous Cysts

Epidermoid cysts:

• Are round cysts or small bumps that are easy to move with your fingers
• Are usually white or yellow, though people with darker skin may have pigmented cysts
• Range in size from less than 1/4 inch to nearly 2 inches (a few millimeters to 5 centimeters) in diameter
• Occur on nearly any part of your body, including your fingernails, but are found most often on your face, trunk and neck

Sometimes an epidermoid cyst has a central opening — the remnant of a hair follicle from which the cyst originally formed — that's plugged by a tiny blackhead. You may be able to squeeze out a thick, cheesy material through this opening, but because of the risk of infection and scarring, it's best to leave this to your dermatologist.

Milia — tiny, deep-seated whiteheads that never seem to come to the surface of your skin — are miniature epidermoid cysts. They're especially common in older women and in men with significant sun damage on their cheeks and temples. They can also be caused or aggravated by long-term use of oil-based creams or cosmetics.

Signs and symptoms of infection, which can occasionally occur, include:

• A thick, yellow material draining from the cyst that may have a foul odor
• Redness, swelling and tenderness around the cyst

A similar looking condition

Sometimes you may develop a small bump on your scalp that looks like an epidermoid cyst. These are almost always pilar or trichilemmal cysts, which usually have thicker walls than epidermoid cysts do and almost always move freely under your skin. The lining of this type of cyst differs slightly from that of an epidermoid cyst.

Diagnosis of Sebaceous Cysts

In most cases, your doctor can diagnose an epidermoid cyst based on its appearance alone, though you may be referred to a dermatologist for treatment.

Treatments of Sebaceous Cysts

Cysts that don't cause cosmetic or functional problems are usually left alone. When a cyst is inflamed, ruptured or infected, these treatment options exist:

• Corticosteroid injections. Your doctor may inject an inflamed, but uninfected, epidermoid cyst with a corticosteroid to help reduce the 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.
• Total excision. This surgical technique removes the entire cyst and so prevents recurrence. Excision is most effective when the cyst isn't inflamed. Your doctor may recommend first treating the inflammation with antibiotics, steroids, or incision and drainage and then waiting to perform excision for four to six weeks after inflammation resolves. Total excision requires sutures. Your doctor will remove sutures in your face within a week or so of total cyst excision, and will remove sutures elsewhere in your body within one to two weeks.
• Minimal excision. Some doctors prefer this technique because it removes the whole cyst wall but causes minimal if any scarring. During the procedure, your doctor makes a tiny incision in the cyst, expresses the contents, and then removes the cyst wall through the incision. The small wound is usually left to heal naturally.
• Lasers. To minimize scarring, your doctor may use a carbon dioxide laser to vaporize an epidermoid cyst on your face or other sensitive area.

Prevention of Sebaceous Cysts

There's no real way to stop epidermoid cysts from forming, but avoiding excessive sun exposure and using oil-free skin care products can help prevent milia. To prevent scarring and infection, don't try to squeeze cysts yourself.

When to seek Medical Advice

Most epidermoid cysts aren't harmful, but you may want to have them removed for cosmetic reasons. See your doctor if you have a cyst that:

• Grows rapidly
• Ruptures
• Becomes painful
• Occurs in a spot that's constantly irritated