Both cause circular growths or lumps on the skin and can look similar. A boil looks like a large pimple—a swollen ring of red with one or more white or yellow pus-filled sores (pustules).

"A boil is a generic term for a pus-filled bump under the skin," says Dr. Gohara. Causes of boils: "Pus in the skin generally connotes an infection with bacteria such as staph aureus" (a type of ...