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.
hough they’re not cancerous, sebaceous cysts can be irritating. A sebaceous cyst is a small lump or bump under the skin. Usually a sebaceous cyst grows very slowly and doesn’t cause pain. However, they can become inflamed or infected, with the overlying skin becoming red, tender, and sore.
Sebaceous cysts form out of your sebaceous gland. The sebaceous gland produces the oil called sebum that coats your hair and skin. Cysts can develop if the gland or its duct, the passage where oil is able to leave, becomes damaged or blocked. This usually occurs due to a trauma to the area.