What is it?
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 lance 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.
A boil usually appears suddenly as a painful pink or red bump that's generally between 1/2 inch to 3/4 inch (1 to 2 centimeters) in diameter. The surrounding skin also may be red and swollen.
Within a few days, the bump fills with pus. It grows larger and more painful, sometimes reaching golf ball size before it develops a yellow-white tip that finally ruptures and drains. Boils generally clear completely in a couple weeks, though it can take a month or more. Small boils usually heal without scarring, but a large boil may leave a scar.
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.
Boils can resemble the inflamed, painful lumps caused by cystic acne. But compared with acne cysts, boils are usually redder or more inflamed around the border and more painful.
A carbuncle is a cluster of boils that often occurs on the back of the neck, shoulders or thighs. Carbuncles cause a deeper and more severe infection than single boils do. Also, carbuncles both develop and heal more slowly and are likely to leave a scar. Carbuncles sometimes occur with tiredness, a fever and chills.
Boils usually form when one or more hair follicles — the tube-shaped shafts from which hair grows — become infected with staph bacteria (Staphylococcus aureus). These bacteria, which normally inhabit your skin and sometimes your throat and nasal passages, are responsible for a number of serious diseases, including pneumonia, meningitis, urinary tract infections and endocarditis — an infection of the lining of your heart. They're also a major cause of hospital-acquired infections and food-borne illnesses.
Staph bacteria that cause boils generally enter through a cut, scratch or other break in your skin. As soon as this occurs, specialized white blood cells called neutrophils rush to the site to fight the infection. This leads to inflammation and eventually to the formation of pus — a mixture of old white blood cells, bacteria and dead skin cells.
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 dermatitis, 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.
- Blood poisoning. In some cases, bacteria from a boil can enter your bloodstream and travel to other parts of your body. The spreading infection, commonly known as blood poisoning (sepsis), can rapidly become life-threatening. Initially, blood poisoning causes signs and symptoms such as chills, a spiking fever, a rapid heart rate and a feeling of being extremely ill. But the condition can quickly progress to shock, which is marked by falling blood pressure and body temperature, confusion, clotting abnormalities and bleeding into the skin. Blood poisoning is a medical emergency — untreated, it can be fatal.
- MRSA. Another potentially serious problem is the emergence of a drug-resistant strain of Staphylococcus aureus. Methicillin-resistant Staphylococcus aureus (MRSA) is highly contagious and spreads rapidly in crowded or unhygienic situations, or where athletic equipment or towels are shared. Although it responds well to several other antibiotics, MRSA is resistant to penicillin, and can be very difficult to treat.
Doctors usually diagnose boils and carbuncles by considering signs and symptoms and medical history and looking at the distinctive sores.
If you have recurring infections, infections that don't respond to standard treatment or have a weakened immune system, your doctor may culture the drainage. During this test, your doctor uses a sterile swab to gently remove a small bit of pus or drainage from the boil or carbuncle. The sample is then cultured in a laboratory for the presence of bacteria.
Treatments and drugs
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 usually includes draining the boil with an incision and sometimes taking antibiotics:
- Incision and drainage. Your doctor may drain a large boil or carbuncle by making a small incision in the tip. This relieves pain, speeds recovery and helps lessen scarring. Deep infections that can't be completely drained may be packed with sterile gauze so that pus can continue to drain.
- Antibiotics. Sometimes your doctor may prescribe antibiotics to help heal severe or recurrent infections, or infections that may be caused by MRSA.
For small boils, these measures may help the infection heal more quickly and prevent it from spreading:
- Apply a warm washcloth or compress to the affected area. Do this for at least 10 minutes every few hours. If possible, first soak the cloth or compress in warm salt water. This helps the boil rupture and drain more quickly.
- Never squeeze or lance a boil yourself. This can spread the infection.
- 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.
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.
- Thoroughly clean even small cuts and scrapes. Wash the wound well with soap and water and apply an over-the-counter antibiotic ointment.
- 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.