Overview

A boil is a painful, pus-filled bump that forms under your skin when bacteria infect and inflame one or more of your hair follicles. A carbuncle is a cluster of boils that form a connected area of infection under the skin.

Boils (furuncles) usually start as reddish or purplish, tender bumps. The bumps quickly fill with pus, growing larger and more painful until they rupture and drain. Areas most likely to be affected are the face, back of the neck, armpits, thighs and buttocks.

You can usually care for a single boil at home. But don't attempt to prick or squeeze it — that may spread the infection.