Armpit boils arise from an infection of the hair follicle under the arm. The infection creates large lesions that form under the armpit and are usually filled with a clear fluid called pus. The infected area may become red and inflamed; it may also easily become irritated when clothes rub across the surface. Individuals experiencing armpit boils may feel pain and discomfort under the arms. The infection at the source of armpit boils may arise from multiple causes.
Poor hygiene can cause armpit boils because of the dirt that is trapped within the hair follicle. Failure to bathe regularly can cause excess dirt, sweat and bacteria to collect under the armpit, causing a painful boil to appear. The boil may be either red or dark in color and is usually sensitive to the touch. According to the Better Health Channel, armpit boils may occur due to buildup of dead skin cells and bacteria on the skin under the arm. If an opening such as a cut is present on the surface of the skin, bacteria may enter and form boils.
Armpit boils in women may occur as a result of excessive underarm shaving, which can lead to an ingrown hair under the arm. The hair will grow under the surface of the skin and form a large boil as a result. According to New York University Langone Medical Center, the boil will soften with time, which can cause a large pus-filled head to form at the top of the boil. A doctor should be notified of the condition if it is accompanied by a fever. Boils can also be contagious if popped or allowed to drain.
Staph bacteria are present on the skin's surface and can be found in the nose, armpits or other warm creases of the skin. If a Staph bacterium enters an open sore, it can cause a boil. According to Hope College Health Center, boils may occur as a result of a Staph infection developing around the armpit and usually heal on their own. Staph infections are most common in areas that are covered with body hair, which makes the armpit an ideal place for the bacteria to dwell.