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What Are Boils?

A boil is a skin infection that starts in a hair follicle or oil gland. At first, the skin turns red in the area of the infection, and a tender lump develops. After four to seven days, the lump starts turning white as pus collects under the skin. If the infection spreads to the deeper tissues of the skin, then it becomes an abscess or furuncle.

  • The most common places for boils to appear are on the face, neck, armpits, shoulders, and buttocks.
  • If several boils appear in a group, this is a more serious type of infection called a carbuncle.

Inflammation of hair follicles is called folliculitis, which can develop into a boil. This is common in the pubic area, especially after shaving.

Hidradenitis suppurativa, also called acne inversa, is a skin condition characterized by lumps under the skin, which often resemble pimples, particularly in the armpits, groin, and buttocks. It looks like boils but is not the same condition.

What Causes Boils?

Boils are usually caused by a bacteria called Staphylococcus (staph). Some staph infections develop into abscesses and can become serious very quickly. This germ can be present on normal skin and enters the body through tiny breaks in the skin or by traveling down a hair to the follicle.

The tiny breaks in the skin may be caused by cuts, scrapes, shaving, ingrown hairs, insect bites, or even skin diseases or conditions.

Medically Reviewed by a Doctor on 10/20/2017

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The eMedicineHealth doctors ask about Boils:

Boils - Experience

Did you have any complications from your boils? Please describe your experience with boils.

Boils - Causes

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Boils - Effective Treatments

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Staph is the cause of most boils.

Causes of Boils


Staphylococcus bacteria (also termed staph) are responsible for a number of common infections.

Sometimes the infections are relatively limited (such as a sty, boil, furuncle, or carbuncle), but other times they may spread to other skin areas (causing cellulitis, folliculitis, or impetigo). Unfortunately, these bacteria can reach the bloodstream (bacteremia) and end up in many different body sites, causing infections (wound infections, abscesses, osteomyelitis, endocarditis, pneumonia) that may cause severe harm or even be fatal.

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