Boils and carbuncles are painful, pus-filled bumps that form under your skin when bacteria infect and inflame one or more of your hair follicles.
Boils (furuncles) usually start as red, tender lumps. The lumps quickly fill with pus, growing larger and more painful until they rupture and drain. A carbuncle is a cluster of boils that form a connected area of infection under the skin.
You can usually care for a single boil at home, but don't attempt to prick or squeeze it — that may spread the infection. Call your doctor if a boil or carbuncle is extremely painful, lasts longer than two weeks or occurs with a fever.
Boils can occur anywhere on your skin, but appear mainly on your face, neck, armpits, buttocks or thighs — hair-bearing areas where you're most likely to sweat or experience friction. Signs and symptoms of a boil usually include:
A painful, red bump that starts out about the size of a pea
Red, swollen skin around the bump
An increase in the size of the bump over a few days as it fills with pus (can sometimes reach the size of a baseball)
Development of a yellow-white tip that eventually ruptures and allows the pus to drain out
A carbuncle is a cluster of boils that form a connected area of infection. Carbuncles often occur on the back of the neck, shoulders or thighs. Compared with single boils, carbuncles cause a deeper and more severe infection and are more likely to leave a scar. People who have a carbuncle often feel unwell in general and may experience fever and chills.
When to see a doctor
You usually can care for a single, small boil yourself. But see your doctor if you have more than one boil at a time or if a boil:
Occurs on your face
Worsens rapidly or is extremely painful
Causes a fever
Is more than 2 inches (5 centimeters) across
Hasn't healed in two weeks
Most boils are caused by Staphylococcus aureus, a type of bacteria commonly found on the skin and inside the nose. Boils sometimes develop at sites where the skin has been broken by a small injury or an insect bite, which gives the bacteria easy entry.
Although anyone — including otherwise healthy people — can develop boils or carbuncles, the following factors can increase your risk:
Close contact with a person who has a staph infection. You're more likely to develop an infection if you live with someone who has a boil or carbuncle.
Diabetes. This disease can make it more difficult for your body to fight infection, including bacterial infections of your skin.
Other skin conditions. Because they damage your skin's protective barrier, skin problems, such as acne and eczema, make you more susceptible to boils and carbuncles.
Compromised immunity. If your immune system is compromised for any reason, you're more susceptible to boils and carbuncles.
Rarely, bacteria from a boil or more commonly, a carbuncle, can enter your bloodstream and travel to other parts of your body. The spreading infection, commonly known as blood poisoning (sepsis), can lead to infections deep within your body, such as your heart (endocarditis) and bone (osteomyelitis).
Although it's not always possible to prevent boils, especially if you have a compromised immune system, the following measures may help you avoid staph infections:
Wash your hands regularly with mild soap. Or, use an alcohol-based hand rub often. Careful hand-washing is your best defense against germs.
Keep wounds covered. Keep cuts and abrasions clean and covered with sterile, dry bandages until they heal.
Keep personal items personal. Avoid sharing personal items, such as towels, sheets, razors, clothing and athletic equipment. Staph infections can spread via objects, as well as from person to person. If you have a cut or sore, wash your towels and linens using detergent and hot water with added bleach, and dry them in a hot dryer.
Although you're likely to see your family doctor or a general practitioner first, you may be referred to a specialist in skin diseases (dermatologist) or infectious diseases.
What you can do
Write down all your signs and symptoms and when they first occurred. Record how long the lesions lasted and if any recurred. Make a list of all medications — including vitamins, herbs and over-the-counter drugs — that you're taking. Even better, take the original bottles and a written list of the dosages and directions.
For boils and carbuncles, some basic questions to ask your doctor include:
Are tests needed to confirm the diagnosis?
What is the best course of action?
Is there a generic alternative to the medicine you're prescribing?
Can I wait to see if the condition goes away on its own?
What can I do to prevent the infection from spreading?
What skin care routine do you recommend while the condition heals?
What to expect from your doctor
Your doctor is likely to ask you a number of questions, such as:
What did the boil look like when it first started?
Are your symptoms painful?
Have you had a boil or carbuncle before?
Are you having fever or chills?
Do you have artificial heart valves, joints or other implanted devices?
Doctors usually can diagnose boils and carbuncles simply by looking at them. But if you have recurring infections or an infection that hasn't responded to standard treatment, your doctor might suggest sending a sample of the pus to a lab for testing.
Many varieties of the bacteria that cause boils have become resistant to certain types of antibiotics, so this test can help determine what type of antibiotic would work best in your particular situation.
You can generally treat small boils at home by applying warm compresses to relieve pain and promote natural drainage.
For larger boils and carbuncles, treatment may include:
Incision and drainage. Your doctor may drain a large boil or carbuncle by making a small incision in the tip. Deep infections that can't be completely drained may be packed with sterile gauze to help soak up and remove additional pus.
Antibiotics. Sometimes your doctor may prescribe antibiotics to help heal severe or recurrent infections.
For small boils, these measures may help the infection heal more quickly and prevent it from spreading:
Warm compresses. Apply a warm washcloth or compress to the affected area several times a day. This helps the boil rupture and drain more quickly.
Never squeeze or lance a boil yourself. This can spread the infection.
Prevent contamination. Wash your hands thoroughly after treating a boil. Also, launder clothing, towels or compresses that have touched the infected area, especially if you have recurrent boils or carbuncles.
Tea tree oil, which is extracted from the leaves of the Australian tea tree (Melaleuca alternifolia), has been used for centuries as an antiseptic, antibiotic and antifungal agent. It's also used topically to treat boils, although there's no strong scientific evidence that it's beneficial.
Tea tree oil can cause allergic reactions in some people, so be sure to stop using it and tell your doctor if you have any problems with its use.