Epidermoid cysts, also called sebaceous, keratin, or epithelial cysts, are small, hard lumps that develop under the skin. These cysts are common and they grow slowly. Occasionally they become inflamed, but are rarely infected. Epidermoid cysts are often found on the face, head, neck, back, or genitals. They look like a small bump, are tan to yellow in color, and are filled with thick, smelly matter. They do not usually cause any pain. Typically these cysts are ignored, but if they become troublesome, they can be excised, injected with intralesional steroid to shrink them down, and occasionally treated with antibiotics.