A boil is an
infection of a follicle (hair cell) which causes painful
swelling, inflammation and an accumulation of fluid under the
skin. The medical name for this condition is folliculitis.
When several boils occur in a cluster, it is called a
carbuncle. In the Western world, the most common cause is
staphylococcal bacteria, which travels down the hair to its
root. In some cases, the bacteria can also enter the body
through tiny cracks or scratches in the skin. Boils can also
occur when foreign matter such as a splinter becomes lodged
under the skin. In cases of acne, boils are formed by infected
sweat glands. In parts of Africa, boils may be caused by
myiasis carried by insects.
A boil consists of a red, swollen area surrounding a pocket of
white blood cells mixed with bacteria and proteins, a mixture
commonly called pus. Pressure builds up as the boil grows,
becoming very painful. In most cases, the boil will open and
discharge the pus spontaneously. In severe cases, it may be
necessary to lance the boil. Boils occur most commonly on the
buttocks, face, neck, armpits and shoulders. When one appears
on an eyelid, it is called a sty.
Boils can result from poor nutrition and bad hygiene as well
as certain health conditions such as diabetes and obesity. The
condition is sometimes caused by exposure to irritating
chemicals. Persons whose immune systems have become
compromised are at high risk, and the condition is sometimes
seen in patients who are on immunosuppressant drugs. Cortisone
medications such as prednisone and prednisolone are commonly
used medications that can cause this effect. Diseases that
disrupt the operation of the immune system, such as
hypogammaglobulinemia, are often accompanied by boils. The
condition sometimes occurs in cancer patients who are on
chemotherapy. Cases of kidney failure are often accompanied by
If a boil occurs in an area where continuous pressure may be
applied to it, this can greatly increase the severity of the
infection. If possible, one should note an infected hair as
soon as it begins to develop and avoid placing pressure on it.
If the pus does not discharge soon after forming a head,
lancing should be performed. Failure to take these precautions
may cause the condition to be more severe than necessary.
In extreme cases, boils can cause sepsis posing a serious
threat to health, producing symptoms of fever and lethargy.
Fatalities are rare but not unknown. Permanent scarring may
occur. Boils may appear internally and cause damage to organs
such as the brain, spinal cord and kidneys. Severe boils pose
a particular risk to persons with heart murmurs, since these
patients have an elevated risk of sepsis.