Boils and cysts both look like bumps on your skin. The main difference between a cyst and a boil is that a boil is a bacterial or fungal infection, and is more likely to be painful.

A boil (furuncle) is a painful skin bump filled with pus. Typically, the cause is staph bacteria that are naturally present on your skin. These bacteria can lead to an infection or inflammation within a hair follicle or oil gland. A fungal infection may also cause some boils.

Boils can appear anywhere on your body. A boil is also called:

  • an abscess (if it’s large)
  • a stye (if it’s on the eyelid)
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A boil is a painful skin bump filled with pus.
Photography by DermNet New Zealand

Symptoms of a boil

Boils are usually small, but they can be as large as a baseball. They begin as pimples that are red in appearance.

Symptoms include:

  • redness
  • swelling
  • pain
  • development of a white or yellow center
  • oozing pus or crusting
  • fatigue or fever
  • general feeling of malaise

Where do boils form?

Staph bacteria normally live on your skin or in your nose. When your skin is scraped or broken, the bacteria can enter via a hair follicle and cause an infection. The boil that forms is the result of your body’s immune system trying to get rid of the bacteria.

The hair follicle can be located anywhere on your body. Boils most often are found in skin areas where there’s friction, like the:

  • neck
  • breasts
  • face
  • armpits
  • buttocks
  • thighs

It can be easy to confuse boils with carbuncles or cysts, but there are differences.

A carbuncle is simply a few boils grouped together. A cyst, on the other hand, is a smooth, round, closed sac under your skin filled with fluid or semisolid material.

Boils and cysts can both look like bumps on your skin. The main difference between a cyst and a boil is that a boil is a bacterial or fungal infection.

Most cysts are slow-growing and benign (noncancerous), and they aren’t contagious. Boils, on the other hand, can spread bacteria or fungi on contact.

The following table gives an overview of the differences between a boil, a cyst, and a carbuncle:

TypeSymptomsCausesRisk factorsTreatment
Boilpresents as a red pimple that may swell and ooze; grows rapidly and is usually painfulresults from a bacterial or fungal infectionrisk factors include skin conditions like acne, psoriasis, or eczema; close contact with someone who has a boil; compromised immune system; diabetes; obesityapplying a warm, moist compress; keeping a clean bandage over the boil; avoiding
picking; if symptoms don’t improve, draining the puss, cleansing the area, and treating with antibiotics may be necessary
Carbunclesimilar to single boils but may be accompanied by fever; often occurs at the back of the neck and extends deeper into the tissue than boilssimilar to boils, caused by an infection, most commonly from staph bacteriasimilar risk factors to boilssimilar to boils, but even more important to release the puss either with a drawing salve ointment or surgical draining followed by cleansing the wound; antibiotics may be necessary and may be administered intravenously
Cystpresents as a smooth nodule under the skin that’s movable, grows slowly, and usually isn’t painful unless inflamedthe cause of many cysts is unknown but may include an injury, swollen hair follicle, the human papillomavirus (HPV), or chronic ultraviolet light; some types of cysts may be hereditary, and some are associated with disorders like Gardner’s syndromepeople assigned male at birth may be more at risk since most types of cysts are more common in them than in people assigned female at birthmost cysts need no treatment, and they may disappear on their own, but they may recur; treatment can involve antibiotics or surgery to drain the cyst (usually if the cyst can move under the skin)

Do not pick at or pop a boil.

Boils can be open sores and drain pus, so if you touch the area with contaminated hands, you risk spreading the bacteria elsewhere or introducing new bacteria into the boil.

Depending on the severity of the boil, a doctor can surgically drain the pus.

Since boils are most commonly caused by an infection by bacteria like staph, the best prevention strategy is to keep good hygiene habits.

In addition to regular hand washing, it’s important to clean and cover any cuts and scrapes. Avoid touching other people’s cuts or bandages, or sharing personal items that come in contact with the skin like razors or towels.

Cover any exercise equipment during use so you do not touch it directly. Clean and disinfect common surfaces that you touch daily, especially if there are any bodily fluids like blood, urine, or vomit.

It’s possible to contract the staph bacteria, which is the most common bacteria to cause a boil. Other bacteria or fungi may also be contagious.

It’s best to avoid touching your boil. But if you do, make sure to wash your hands thoroughly beforehand for at least 15 seconds, especially before eating and after using the toilet, exercising, coughing, sneezing, or blowing your nose.

Take care if someone you work with or live with currently has a boil. Wash any towels, toys, or clothing that may have come in contact with the boil. To kill any bacteria or fungi that may be present on these items, use hot water and soap. Dry the items in a dryer using the hot setting.

Most boils heal on their own within 1 to 3 weeks. But if the boil swells or begins to cause you increasing pain, contact a dermatologist for evaluation and treatment.

If another boil appears, or if you suddenly have a fever or vision problems, you should also contact a doctor.