Epidermoid cysts, also called sebaceous, keratin, or epithelial cysts, are small, hard lumps that develop under the skin. These cysts are common. They grow slowly. They do not cause other symptoms and are nearly never cancerous. Epidermoid cysts are often found on the face, head, neck, back, or genitals. They can range in size from 1/4 inch to 2 inches across. They look like a small bump, are tan to yellow in color, and are filled with thick, smelly matter. They do not cause any pain and can usually be ignored.
Epidermoid cysts are usually caused by a buildup of keratin. Keratin is a protein that occurs naturally in skin cells. Cysts develop when the protein is trapped below the skin because of disruption to the skin or to a hair follicle. These cysts often develop in response to skin trauma, HPV infection, acne, or excessive exposure to the sun. An epidermoid cyst is more likely to develop in people with acne or other skin conditions.
To diagnose epidermoid cysts, a physician will examine the bump and surrounding skin, as well as take a medical history. They will ask for details on how long the bump has been present and whether it has changed over time. Physicians can usually diagnose an epidermoid cyst by examination only, but sometimes an ultrasound or a referral to a dermatologist is needed to confirm the diagnosis.
Most epidermoid cysts either stop growing or go away on their own without treatment. Physicians will usually make note of a cyst and monitor it during each checkup to make sure that it has not changed. Since epidermoid cysts are very rarely cancerous, they do not pose a risk. Most are never treated.
Treatment may be required if the cyst becomes red, swollen, painful, changes in size or character, or is infected. In such cases, treatment options include antibiotics and drainage. Sometimes the cyst may need to be surgically removed. It can also be removed for cosmetic reasons.
In most cases, epidermoid cysts cause no long-term problems. Squeezing out the contents of the cyst on your own can lead to infection, so it’s best to leave the cyst alone.
Once a cyst is drained, there is a possibility that it will grow back. Very rarely, epidermoid cysts can become cancerous. Any significant change in a cyst is reason to see your doctor.