A cyst is a fluid-filled lump that forms in the deeper layers of skin when a hair follicle becomes blocked. They can be uncomfortable and unsightly but are harmless (benign). Nevertheless, any suspicious growth on the skin should be examined by a dermatologist to determine whether it is cancerous. If infected, a cyst may require treatment with antibiotics. Patients with large or painful cysts may choose to undergo minor surgery. Cysts can occur anywhere on the body but commonly appear on the face and scalp, trunk and fingernails. They include acne whiteheads and comedones, milia, and dermoid, epidermal, trichilemmal and pilar cysts.