A furuncle, also called a boil, is a bump on the skin filled with pus caused by an infection. It can resemble a large pimple, but furuncles are deeper in the skin and tend to be more painful.

A boil—medically known as a furuncle—is a common skin infection that occurs when a hair follicle or oil gland becomes infected. A boil usually appears as a red, painful lump that fills up with pus and ...