Skin boils are inflamed bumps that begin under the surface of the skin when bacteria infect at least one hair follicle (the tubular shafts from which hair grows). This condition is known as folliculitis and it often occurs when hair follicles are damaged by friction from clothing or shaving or when follicles are blocked. Certain populations are at higher risk for developing boils, including individuals with suppressed immune systems, diabetes, obesity or certain skin conditions.

A boil first appears on the skin surface as a red, inflamed lump that fills with pus within 24 hours. The boil is often painful and may continue to swell for several days before it bursts and drains. Boils typically appear on the face, neck, armpits, breasts, buttocks or thighs.

Boils often do not require medical treatment. However, in some cases a physician may need to make an incision in a boil to help it drain. Antibiotics (drugs used to combat bacteria) also are sometimes prescribed to eliminate the infection that causes a boil. In rare cases, infection from a boil can enter the bloodstream, creating a potentially life-threatening condition for the patient.

Patients should contact a physician if their boil lasts longer than two weeks, if they have an associated fever, or if more than one boil appears in a cluster. Children (especially infants) and the elderly should also seek medical attention whenever boils appear. Boils that are painful or that are accompanied by other symptoms also should be examined by a physician.