Boil: Symptoms & Signs

Medically Reviewed on 11/3/2020

A boil is an abscess, or a collection of pus, that forms within the skin. There are different types of boils. Boils can develop anywhere on the body, including the trunk, extremities, buttocks, groin, armpit, or other areas. Boils often occur at the site of hair follicles.

Signs and symptoms of a boil include a painful, red bump that starts out small and can enlarge to more than 2 inches (5 centimeters) and swollen skin around the bump. There is typically an increase in the size of the bump over a few days as it fills with pus, leading to development of a yellow-white tip that eventually ruptures and allows the pus to drain out.

Cause of a boil

Bacterial infections cause boils.

Other boil symptoms and signs

  • Bump Increases in Size Over a Few Days
  • Drainage of Pus
  • Painful, Red Bump on the Skin
  • Swollen Skin Around the Bump
  • Yellow-White Tip on the Bump


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Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.