Boils are painful abscesses on the skin that are usually about the size of a pea, though they can grow to be up to an inch in diameter. They can be found anywhere on the body, but tend to develop on the thighs, buttocks, neck and face. Boils are diagnosed based on their distinctive appearance: they contain white or yellow centers because the boil is filled with pus. There are a few common ways that the skin can become infected.
Ingrown Hair
A boil that involves infection of the hair follicle is clinically called a furuncle. The hair follicle is the shaft that surrounds a growing hair and, when infected, forms a hard swelling filled with pus. A common source of the infection, according to the online medical library MedlinePlus, is the bacteria Staphylococcus aureus. However, other bacteria or fungi that are normally on the skin can potentially infect a hair follicle. The most common way that a hair follicle becomes infected is through an ingrown hair. As the hair grows trapped under the skin, it causes damage to the follicle, making it susceptible to infection.
Once a hair follicle is infected, the infection may spread to other nearby follicles. This leads to the development of carbuncles, which are groups of furuncles that are connected by infected tissue below the skins surface.
A subtype of a furuncle is a pilonidal cyst, which is caused by ingrown hairs in the skin near the crease of the buttocks. This is caused by friction of the skin rubbing over the tailbone. These boils can become severe and often need medical attention, according to the NYU Langone Medical Center.
Lodged Foreign Object
The infection may also gain access to the tissue under the skin due to the lodging of a foreign object under the skin, notes the NYU langone Medical Center. The foreign object is typically a splinter of wood or other hard and sharp object that is able to penetrate and become lodged in the skin. Bacteria or fungi on the surface of the skin then infect the expose wound and a boil develops.
Blocked Oil Gland
Acne is a chronic skin disorder that results in skin boils called pimples. Sebaceous glands secrete oil on the skin via the hair follicle shaft. When these glands become plugged with dried oil and dead skin cells, the follicle may become blocked. The blockage makes possible a skin infection cause by the bacteria Propionibacterium acnes. If the acne infection is superficial, no boils form; however, if the bacteria are able to infect deep into the skin, a boil is likely to develop. If the boil ruptures underneath the skin, it can cause an even larger abscess to develop.
