An epidermoid cyst is a small abnormal growth or lump in the top layers of the skin. It's filled with keratin, the same proteins that make up your hair and nails. An epidermoid cyst may incorrectly be called a sebaceous cyst.
Some general facts about epidermoid cysts:
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An epidermoid cyst is a sac filled with material from skin secretions. It can grow anywhere on the body. But it's most often found on the face, behind the ears, and on the chest or upper back. It often has an open, enlarged pore in the middle of it.
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The material in the cyst is often cheesy, fatty, or oily. The material can be thick (like cottage cheese) or liquid.
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The area around the cyst may smell bad. If the cyst breaks open, the material inside it often smells bad too.
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The cyst is usually firm, and you can usually move it slightly if you try.
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The cyst can be smaller than a pea or as large as a few inches.
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It's usually not painful, unless it becomes inflamed or infected.
Causes
Epidermoid cysts occur when skin (epidermal) cells move under the skin surface, or are covered over by it. These cells continue to multiply, like skin does normally. They then form a wall around themselves (cyst) and secrete normal skin material (keratin). In most cases, epidermoid cysts occur for no known reason. They may also occur because of an injury to the skin or from acne.
Symptoms
When you have an epidermoid cyst:
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You will feel a lump just beneath the skin.
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It may or may not be painful.
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The cyst may or may not smell bad.
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The cyst may become inflamed or red.
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The cyst may leak fluid or thick material.
Home care
Epidermoid cysts often go away without any treatment. If your cyst doesn’t go away and it bothers you, it may be drained or removed. If the cyst drains on its own, it may return. Don't squeeze it, pop it, stick a needle in it, or cut it open. Doing those things can often lead to an infection and scarring. If it gets severely inflamed or infected, seek medical care. Be sure to clean the cyst area when bathing or showering. Watch for the signs of infection listed below.
Follow-up care
Follow up with your health care provider, or as advised.
When to get medical advice
Contact your health care provider right away if you have:
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Swelling, redness, or pain.
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Pus coming from the cyst.
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A fever of 100.4°F (38ºC) or higher, or as advised by your provider.
