A boil is a painful, pus-filled bump that can develop on the surface of your skin. A boil is also called a furuncle. Larger ones are called abscesses. A boil on your eyelid is called a stye.

A boil is often caused by an infection within a hair follicle or oil gland. They’re usually caused by staph bacteria, which are naturally present on your skin. Boils can develop anywhere on your body, but are commonly found in places on the body where there is friction. They’re most likely to occur on your neck, breasts, face, armpits, buttocks, or thighs.

According to a 2012 review article, boils are becoming more common in the United States. This increase has been linked to the increase of methicillin-resistant Staphylococcus aureus (MRSA) bacteria. The bacteria normally found on your skin and inside your nose can become resistant to many types of antibiotics. Infections with these bacteria can become serious and difficult to treat.

Boils typically begin as small red bumps that itch or hurt. Over a few days, a boil will swell as it fills with bacterial pus. It will typically develop a whitish-colored tip that breaks open, allowing the pus drain out. The boil may then crust over.

If your boil becomes larger or if the infection spreads, you might have other symptoms. These include a general ill feeling, fatigue, or fever.

Not all red bumps on your skin are boils. Examples of skin conditions that can look like boils include:

Bacteria that are normally present on your skin can infect a hair follicle and inflame the surrounding area, causing a boil to form. Often bacteria get trapped in a hair follicle or oil gland due to friction or trauma to the skin.

Inner thighs are a common site for boils because your thighs can rub against each other and get sweaty, especially in hot and humid weather. This encourages bacteria to grow within the follicles.

Anyone can get boils. You can be healthy and have boils. But some conditions make you more susceptible. For example:

  • If you have eczema or psoriasis, you may have skin scratches or sores that can become infected.
  • If your immune system is compromised, you may be more likely to develop an infection.
  • If you have diabetes, it may be harder for you to fight off infection.
  • If you live or work with someone else who has a boil, you’re more likely to develop one.
  • If you’re obese, you may be more likely to get boils.

Most boils clear up on their own within a week or so, without complications. But if you have a boil on your inner thigh or other body part that lingers, becomes larger and more painful, or comes back, you should see a doctor.

Serious symptoms

Small boils typically do not cause symptoms to other parts of your body. However, if the infection spreads, it can become serious. You may notice:

  • body aches
  • fever
  • chills
  • feeling poorly overall

Any of these symptoms require immediate medical attention. This is because skin infections that are left untreated can spread to the blood stream and become life-threatening.

Large boils

If the boil becomes large enough and doesn’t drain on its own, your doctor may perform a procedure in the office. It’s called an incision and drainage, or I&D. They will make a small nick in the boil to drain the pus. They’ll also usually send a sample of the pus to a laboratory.

Lab technicians can help identify the particular bacteria causing your infection. This can help your doctor decide which antibiotics are best for treatment, if needed. Depending on the size, location, and other symptoms of your boil, draining it may be enough to cure the infection. Antibiotics are only used for large infections and in certain situations.

Recurring boils

If your boil recurs frequently, or if you develop complications, your doctor may refer you to a skin disease specialist, also known as a dermatologist. Or they may refer you to an infectious disease specialist.

In many cases, you may be able to treat your boil at home. If home treatment doesn’t work, your doctor may prescribe other treatments.

At home

It's important not to squeeze or pop a boil yourself. Doing so can spread the bacteria inside to deeper parts of your skin. Instead, apply a warm compress regularly throughout the day, which will help the boil drain on its own.

The American Academy of Dermatology (AAD) recommends applying a warm compress for 10 to 15 minutes 3 to 4 times a day until the boil heals. You can make a warm compress by soaking a clean washcloth in hot water. Make sure the water isn’t too hot.

If the boil is draining or in an area of friction, you should apply a clean bandage. This can limit the irritation. It's hard to avoid friction in your inner thighs, but you may want to wear loose underwear and clothing to avoid aggravating the boil.

The AAD suggests taking ibuprofen or acetaminophen to relieve pain caused by your boil, if needed.

At the doctor's office

If your doctor can’t perform an incision and drainage in the office due to the boil’s location or size, you may need to see a surgeon. In some cases, after the boil is drained gauze is used to pack the wound. If this occurs, you will likely need to return to your doctor daily to change the gauze.

For larger infections and abscesses, your doctor may order an ultrasound image of the area. This is to make sure the pus has been fully drained. They may also order an ultrasound if they suspect you have a boil under your skin that’s not visible on the surface.

Your doctor may prescribe antibiotics by mouth. More serious infections may require hospitalization and intravenous antibiotics.

If you squeeze or prick your boil, you can spread the infection to other parts of your skin. If the infection spreads, the boil can grow larger and become an abscess. This is a deep pocket of pus that can be as big as a grapefruit. An abscess requires urgent medical attention.

Sometimes, other boils will erupt around the first one. A grouping of boils is called a carbuncle. Carbuncles are more painful. They are more likely to cause serious symptoms and leave a scar.

If the infection spreads, there is a chance that the bacteria can enter your bloodstream and infect other parts of your body, including your heart, bones, and brain.

In most cases, though, boils heal without complications.

Your boil should typically clear up within one week or so of home treatment.

When you have a boil, it’s important to practice good hygiene. This can help prevent the spread of infection to other parts of your body and to other people. For example:

  • Don't share personal items, like razors, that might have come in contact with an infection.
  • Wash towels, compresses, and any clothing that may have come in contact with a boil. Use soap, hot water, and a hot dryer to launder them and kill any bacteria.
  • If the boil is draining, keep the wound covered with a dry bandage until it heals. You may want to use a wide bandage around your thigh to decrease irritation from chafing.
  • Change the bandages regularly to keep the boil clean and dry.
  • Wash your hands frequently and thoroughly.