A boil is a bacterial skin infection that starts in a hair follicle or oil gland, usually after bacteria enter through a small cut or scratch. Boils are most often found on the face, neck, shoulders, armpits, or buttocks.

They typically begin as red, tender lumps that become larger and fill with pus over a few days. The tip of the boil often turns white as the pus collects beneath the skin.

When to See a Doctor:

Boils often resolve on their own, but you should seek medical care if the boil doesn’t drain, gets worse, or is accompanied by fever or chills—these could be signs of a spreading infection.