What is an epidermal cyst?

An epidermal cyst is a growth that develops on the skin. It is also known as epidermoid, sebaceous or keratin cyst. These typically benign masses are most often found in the areas from the neck to the top of the head and trunk, although they can grow anywhere on the skin. They are among the most common types of cysts. Most epidermal cysts can be ignored and may even go away on their own, but in some cases they may need to be removed.

Many epidermal cysts begin to grow due to swelling of the hair follicles. The blockage caused by the contraction of the space in the follicle results in a reservoir of fluid and the accumulation of cells known as keratin. When this material cannot properly exit the body, it builds up until it eventually becomes a cyst. The growth can also occur as a result of trauma to the skin, such as with surgery.

Rarely, an epidermal cyst can become painful and inflamed, or develop abscesses. If the lump becomes uncomfortable or infected, it may be injected with steroids to make it shrink. Larger cysts may need to be surgically removed. Applying moist heat to the cyst, such as with a damp cloth, may also help it drain on its own. Once a cyst has been cleared, the area will usually heal permanently, although the growth may return.

The material in an epidermal cyst is usually a combination of a thin, oily fluid and a thicker mass similar in texture to soft cheese. In most cases, the liquid is harmless. If bacteria enter the cyst, there may also be pus due to infection.

Although most epidermal cysts can be safely ignored, they can be similar in appearance and texture to other more serious growths on the skin. If a growth does not go away after application of moist heat, it is usually advisable to have it examined by a doctor so that conditions such as cancer can be ruled out. Most cysts will develop over a long period of time and perhaps even several years.

Milia is a common type of epidermal cyst. These growths are smaller than the typical variety and usually grow in groups. Babies often develop milia, although they can be found at any age. Milia can also develop as a result of procedures such as dermabrasion or after blistering of the skin.

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