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What is a boil?

A boil, sometimes also referred to as a furuncle, is an infection involving a hair follicle on the skin. Boils are typically caused by Staphylococcus aureus bacteria, although they may be caused by other bacteria or fungi present on the skin surface. In addition to affecting the hair follicle, infections that cause boils will also typically involve the surrounding skin.

Boils form when bacteria from the skin surface infiltrate a hair follicle. This intrusion of bacteria triggers an immune response that includes drawing white blood cells into the infected follicle to fight the infection. If the infection in the follicle is not cleared quickly, pockets of bacteria, dead cells, and fluids can develop, resulting in the formation of a boil.

Boils may form individually or be grouped together. When multiple boils fuse together to become one lump, the resulting lump is called a carbuncle. Boils may occur anywhere on the body, although they are most commonly located in the armpits or on the buttocks, face, neck or thighs. Although there is no specific cause for the formation of boils, poor hygiene or conditions that weaken the immune system can lead to increased susceptibility.

Before boils can heal completely, they must open and drain. Boils typically resolve on their own within two weeks of onset.

Seek prompt medical care if a boil lasts for longer than two weeks, is recurrent, is located in the middle of the face or on the spine, or is accompanied by other symptoms, including a fever, an excessive amount of fluid around the boil, or the presence of red streaks coming from the boil.

What are the symptoms of a boil?

Boils exhibit multiple symptoms, including the formation of rigid, sensitive, swollen, bright red areas in the skin. Boils become more painful and less rigid as they develop. Typically, a boil should clear up in two weeks or less. If you have a boil that lasts for more than two weeks, contact your health care professional.

Common symptoms of boils

You may notice symptoms of boils daily or just once in a while. At times, any of these symptoms can be severe:

  • Fatigue

  • Fever not associated with flu symptoms

  • Fluid leakage from the boil, which may crust over

  • Itching feeling

  • Rigid, sensitive reddened area of skin ranging in size from a few millimeters to several centimeters

  • Tenderness or pain

  • White or yellow centers in the boil (pustule)

Symptoms that might indicate a serious condition

In some cases, boils can be a serious condition that should be evaluated by a health care professional. Seek prompt medical care if you, or someone you are with, have any of these serious symptoms including:

  • Boils located in the middle of the face or on the spine

  • Boils that last longer than two weeks

  • Fever not associated with flu symptoms

  • Recurrent boils

What causes a boil?

A boil develops when a hair follicle becomes infected by bacteria or fungus from the skin. The presence of infection draws in white blood cells from the body’s immune system to combat the infection. However, if the infection does not resolve quickly enough, pockets of bacteria, dead cells, and fluids can develop, resulting in the formation of a boil. Boils are very common and may be caused, in part, by conditions that weaken the immune system, thus increasing an individual’s susceptibility to infection, or by poor hygiene.

What are the risk factors for a boil?

A number of factors increase the risk of developing boils. Not all people with risk factors will get boils. Risk factors for boils include:

  • Conditions that weaken the immune system, such as diabetes or cancer

  • Exposure to a pathogenic strain of Staphylococcus bacteria

  • Family history for tendency to form boils

  • Immunosuppressant drugs, such as cancer chemotherapy

  • Poor hygiene

Reducing your risk of a boil

You may be able to lower your risk of a boil by:

  • Using antibacterial soaps

  • Washing with an antiseptic

  • Maintaining good skin hygiene habits

How is a boil treated?

Boils should heal on their own after several weeks, but will only do so after they are opened and drained. You should never attempt to force a boil to open or drain, since doing so could spread the infection. A boil that is especially deep or large may need to be treated by a health care professional.

Although a boil typically heals on its own within two weeks, the healing process may be facilitated by applying warm, damp cloths or gauze to the boil several times a day. This helps the boil to open and drain.

If medical treatment is required, your health care provider may need to cut open, or incise, the boil to allow drainage of pus and fluid. If you have recurrent or unusually large boils, your health care provider may take a culture of the fluid to identify the type of bacteria or organism responsible for the infection. In serious cases of infection, antibiotics may be prescribed. However, the majority of boils heal on their own without medical treatment.

Once a boil starts to drain, the area around the boil should be cleaned often using a warm, damp cloth or gauze. You should also thoroughly wash your hands or any materials, such as clothing or bed linens, that come into contact with the boil or surrounding area. Dressings applied to boils should be discarded after removal.

What are the potential complications of a boil?

Although rare, serious or life-threatening complications associated with boils may occur if a serious infection develops. If you have boils that are recurrent, last for excessive periods of time, are unusually large or deep, or are associated with a fever, consulting your health care provider can help you avoid serious complications including:

  • Abscess formation

  • Antibiotic resistance (risk of spreading MRSA to others)

  • Encephalitis (inflammation and swelling of the brain due to a viral infection or other causes)

  • Endocarditis (inflammation of the interior lining of the heart and heart valves)

  • Meningitis (infection or inflammation of the sac around the brain and spinal cord)

  • Osteomyelitis (bone infection)

  • Permanent scarring

  • Sepsis (life-threatening bacterial blood infection)

  • Spread of infection elsewhere in the body

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 18
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Boils. PubMed Health, a service of the NLM from the NIH.
  2. Staphylococcal infections. Medline Plus, a service of the National Library of Medicine National Institutes of Health.
  3. Domino FJ (Ed.) Five Minute Clinical Consult. Philadelphia: Lippincott Williams & Wilkins, 2013.