Epidermoid and Pilar Cysts
Epidermoid and pilar cysts are common benign, keratin-filled skin growths, described in the AAFP review of benign skin tumors.
Symptoms
A firm, round, mobile bump under the skin, often with a central punctum (small dark opening); pilar cysts occur almost exclusively on the scalp and often run in families.
Causes and risk
Cysts form when skin cells become trapped beneath the surface instead of shedding normally, sometimes following trauma; pilar cysts have an autosomal dominant inheritance pattern in many cases.
How it is evaluated
Diagnosis is usually clinical; ultrasound can confirm a cyst's well-defined, fluid-like character when the diagnosis is uncertain, and multiple or atypically located epidermoid cysts warrant screening for Gardner syndrome.
Treatment
Complete excision, including the cyst wall, is the definitive treatment to prevent recurrence. Inflamed cysts can be managed with intralesional steroids or drained, with recent cohort data supporting single-stage excision without routine antibiotics.
When to seek care
A cyst that becomes red, warm, swollen, and painful may be inflamed or infected and typically needs incision and drainage; per IDSA guidance, this inflammation is often a foreign-body reaction to ruptured keratin rather than true infection, but fever or spreading redness should prompt urgent evaluation.