A boil, or furuncle, is caused by a bacterial infection and irritation of the skin and its underlying structures. It is a painful swelling in the skin that is easily detected by touch. When a group of boils interconnects below the surface of the skin, a growth called a carbuncle forms.
Causes
Boils develop when Staphylococcus bacteria enter the skin through a hair follicle and multiply in its warm, moist environment. Bacteria continue to grow while producing substances that invade surrounding cells. White blood cells (which attack and kill invading organisms) travel to the infected hair follicle and enclose bacteria.
As more white blood cells gather, they eventually consume the bacteria and eliminate the infection. This buildup by the white blood cells is what produces the pustule (large cyst) in the center of the boil. When the pustule ruptures, pus and dead skin cells killed by the bacteria drain out, and the boil heals.
Staphylococcus bacteria are often found in the nose and throat. From there -- or from other parts of the body -- the bacteria can spread to a hair follicle. The bacteria can also be transmitted via contact with an infected person or an infected article, such as a washcloth or towel. In most cases, however, people who come in contact with the bacteria do not get boils.
Those at Risk
People who are run-down or who suffer diseases such as anemia (deficiency of red blood cells), diabetes, or infections that weaken their natural defenses against bacteria seem more susceptible to boils. Those who work with greasy or oily substances are more likely to develop boils because these materials trap bacteria against the skin. Poor bathing habits also invite infection, especially in the summer months, when sweaty skin provides the moist climate conducive to bacterial growth.
Symptoms
Boils can develop anywhere on the skin. They appear most frequently on the neck, face, and back, and they can erupt in several places during an infection. Although boils vary in size, they characteristically form white or yellow pustules. As the infection progresses, the pustule becomes red and hot. Excess fluid in the boil produces pressure on the nerves underneath, which can result in considerable pain. When boils contain little pus, they are called blind boils; the inflammation recedes slowly without rupturing, but sometimes it leaves a scar.
If boils are large or extensive, the person may also experience fever and a general feeling of weakness. Sometimes, the infection gets into the bloodstream and spreads throughout the body. The same bacteria that cause the boil may also produce a toxin (poison) that causes blood clots, usually in the blood vessels that are around the boil.
Treatment
Boils and carbuncles should never be squeezed, particularly if they are on the face. Squeezing may force the infection deeper into the skin and possibly into the bloodstream. Only a physician is qualified to lance a boil to encourage drainage. Afterward, the doctor may prescribe an oral antibiotic, such as penicillin or erythromycin, to fight further infection.
Many boils will rupture and heal on their own. However, holding a soft cloth soaked with warm water against the boil for 15 to 20 minutes at least four times a day will speed the process. These warm compresses increase blood flow to the area and encourage pustule formation. Since bacteria from the boil are contagious, the cloth should be disinfected in boiling water or in the hot cycle of a washing machine.
When a boil bursts, the infected area should be washed thoroughly and covered with an antibiotic cream and sterile gauze. If the boil does not heal within a few days, or if the boil is located on or near the face, a physician should be consulted.
Prevention
To prevent new eruptions, the skin needs to be kept cool and dry. Physicians sometimes advise their patients to wash the entire body with an antiseptic (germ-fighting) soap twice a day. If boils frequently recur, underclothing and bed linen should be changed on a daily basis.
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