Boil is a painful infection of the skin and tissues under the skin. A boil begins as a hard, red lump. Within a few days, the center of the lump softens and fills with pus. Most boils develop on the face, armpits, chest, and buttocks.
Boils are caused by bacteria called staphylococci. In most cases, the bacteria enter the skin around a hair. The bacteria then multiply beneath the surface of the skin. The body produces white blood cells to fight the bacteria. The white blood cells–and blood serum–fill the center of the boil, forming pus.
Skin tissue sometimes absorbs the pus. However, in the majority of cases, the skin that covers the top of the boil becomes thin and breaks, and the pus drains out. After the pus has drained out of the boil, the boil begins to heal.
Physicians treat boils by applying hot, moist pads and by prescribing antibiotics. In many cases, doctors drain the pus by cutting the skin over the boil. Only a physician should drain a boil because improper cutting may cause the infection to spread through the blood or to other areas of the skin.
A boil is contagious and should be covered with a bandage. Epidemics of boils sometimes result when infected people share towels or clothing with other people. In most cases, boils can be prevented by keeping the skin clean.
