A skin cyst is a sac-like growth that develops beneath the surface of the skin. These cysts are usually benign, meaning they are not cancerous, and they typically contain material such as fluid, semi-fluid substances, or keratin—a protein found in skin, hair, and nails. The most common types of skin cysts are epidermoid cysts and pilar (trichilemmal) cysts.
Epidermoid cysts originate from the epidermis, the outermost layer of the skin, and are filled with keratin. They often appear as small, round bumps under the skin and are most commonly found on the face, neck, or trunk.
Pilar cysts usually form from hair follicles and are most frequently seen on the scalp. Like epidermoid cysts, they contain keratin and are typically smooth, firm, and mobile beneath the skin.
While these cysts are generally harmless and may not cause any symptoms, they can sometimes become problematic. If a cyst becomes inflamed, it may swell, become red, and feel tender or painful. In some cases, the cyst can become infected, leading to the formation of pus and increased discomfort. Rarely, cysts may rupture, releasing their contents and causing further irritation.
Most skin cysts do not require treatment unless they cause pain, discomfort, or cosmetic concerns. If needed, treatment options include drainage, minor surgical removal, or—in the case of infection—antibiotic therapy. It’s important to have any new or changing skin growths evaluated by a healthcare professional to rule out other conditions and to determine the best course of action.