- Risk Factors
What is a boil?
A boil is a localized infection in the skin that begins as a reddened, tender area. Over time, the area becomes firm, hard, and increasingly tender. Eventually, the center of the boil softens and becomes filled with infection-fighting white blood cells from the bloodstream to eradicate the infection. This collection of white blood cells, bacteria, and proteins is known as pus. Finally, the pus "forms ahead," which can be surgically opened or may spontaneously drain out through the surface of the skin. A pus enclosed within tissue is referred to as an abscess.
A boil is also referred to as a skin abscess. Boils can occur anywhere on the body, including the following:
- Other areas
What are the different types of boils?
Several different types of boils include the following:
- Furuncle or carbuncle: This is an abscess in the skin usually caused by an infection with the bacterium Staphylococcus aureus. A furuncle can have one or more openings on the skin and may be associated with a fever or chills. The term furuncle is used to refer to a typical boil that occurs within a hair follicle. The term carbuncle is typically used to represent a larger abscess that involves a group of hair follicles and a larger area than a furuncle. A carbuncle can form a hardened lump that can be felt in the skin. The condition of having chronic, recurrent boils (furuncles or carbuncles) is referred to as furunculosis or carbunculosis, respectively.
- Cystic acne: This is a type of abscess that is formed when oil ducts become clogged and infected. Cystic acne affects deeper skin tissue than the more superficial inflammation from common acne. Cystic acne is most common on the face and typically occurs in the teenage years.
- Hidradenitis suppurativa: This is a condition in which multiple abscesses form under the armpits and often in the groin area. These areas are a result of local inflammation of the sweat glands. This form of skin infection is difficult to treat with antibiotics alone and typically requires a surgical procedure to remove the involved sweat glands to stop the skin inflammation.
- Pilonidal cyst: This is a unique kind of abscess that occurs in the crease of the buttocks. Pilonidal cysts often begin as tiny areas of infection in the base of the area of skin from which hair grows (the hair follicle). With irritation from direct pressure, over time the inflamed area enlarges to become a firm, painful, and tender nodule that makes it difficult to sit without discomfort. These abscesses frequently form after long trips that involve prolonged sitting.
What causes boils to form?
There are many causes of boils. Some boils can be caused by ingrown hair. Others can form as the result of a splinter or other foreign material that has become lodged in the skin. Other boils, such as acne, are caused by plugged sweat glands that become infected.
Often the exact cause of a boil cannot be determined.
The skin is an essential part of our immune defense against materials and microbes that are foreign to our bodies. Any break in the skin, such as a cut or scrape, can develop into an abscess should it become infected with bacteria.
What are risk factors for boils?
Anyone can develop a boil. However, people with certain illnesses or who take certain medications that weaken the body's immune system (the natural defense system against foreign materials or microbes) are more likely to develop boils. Diseases that are associated with impaired immune systems include diabetes and kidney failure. Diseases in which there is inadequate antibody production (such as hypogammaglobulinemia) can also increase the risk of developing boils.
Many medications can suppress the normal immune system and increase the risk of developing boils and other infections. These medications include cortisone medications (prednisone [Deltasone, Liquid Pred] and prednisolone [Pediapred Oral Liquid, Medrol]) and medications used for cancer chemotherapy.
What are the symptoms of boils?
A boil, or skin abscess, is a collection of pus that forms in the skin.
Boils symptoms and signs include the following:
- A firm reddened pea-sized bump
- Tender, swollen skin surrounding the bump
- The bump may increase in size
- Pus-filled head on the bump, which may spontaneously drain, weep, or ooze
Boil vs. pimple
A pimple is a type of skin condition that can appear similar to a boil. Pimples are most commonly seen in people with acne on the face, back, or chest. Pimples may at times be filled with pus (like a boil) in addition to dead skin cells and oily secretions. Like boils, pimples start in pores which are openings for hair follicles in the skin.
A boil is typically reddened and causes more pain than a pimple. Some pimples and boils may be indistinguishable, and these two conditions arise from a similar inflammatory process occurring in the hair follicles, with boils being more severe and representing true infections.
Are boils contagious?
The bacteria present inside the boil can be contagious to others, especially if there is direct skin-to-skin contact with the secretions from an open boil. (See the section on prevention for tips on how to prevent the spread of infection from a boil.)
IMAGESSee a medical illustration of a boil plus our entire medical gallery of human anatomy and physiology See Images
When should someone seek medical attention for a boil?
While boils typically resolve on their own and have an excellent prognosis, there are special situations in which medical care should be sought when boils develop. Rarely, boils may spread or persist, leading to more widespread infections.
Any boil or abscess in a patient with diabetes or a patient with an underlying disease that can be associated with a weakened immune system (such as cancer, rheumatoid arthritis, etc.) should be evaluated by a healthcare professional. Additionally, many medicines, especially prednisone, that suppress the immune system (the natural infection-fighting system of the body) can complicate what would be an otherwise simple boil. Those who are taking such medications should consult their health care professional if they develop boils. (If someone is not sure about his or her medications' effects on the immune system, a pharmacist may be able to explain which medicines to be concerned about.)
Any boil that is associated with a fever should receive medical attention. Increasing reddening of the nearby skin and/or formation of red streaks on the skin (signs that the infection may be spreading), the failure of a boil to "form ahead," and the development of multiple boils are other symptoms that warrant a visit to a health care professional. Medical attention is also required for boils in an infant. Boils located on the face, spine, groin, or rectum may also require medical attention.
A "pilonidal cyst," a boil that occurs between the buttocks, is a special case. These almost always require medical treatment, including drainage and packing (putting gauze in the opened abscess to ensure it continues to drain). Finally, any painful boil that is not rapidly improving should be seen by a healthcare professional.
What kinds of healthcare specialists diagnose and treat boils?
Many boils resolve without specific treatment, but a dermatologist is a doctor commonly consulted for the management of a boil. Other healthcare specialists who may treat boils include a primary care doctor, which may be a family practitioner, pediatrician, or internal medicine doctor. With severe boils or spreading infection, an infectious disease specialist or surgeon may be consulted. Emergency medicine doctors may treat certain cases of severe infection caused by boils or abscesses.
How do healthcare professionals diagnose boils?
The diagnosis of a boil can be made by observation of the typical signs and symptoms. Blood tests or specialized laboratory tests are not required to make the diagnosis of a boil. If the infection within a boil has spread to deeper tissues or is extensive, cultures of the pus may be taken from the wound area to identify the precise type of bacteria responsible for the infection. This can guide the choice of antibiotics for treatment.
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What are boil treatments and home remedies?
Home treatment is an option for most simple boils. Ideally, treatment should begin as soon as a boil is noticed since early treatment may prevent later complications.
The primary home remedy for most boils is heat application, usually with hot or warm water soaks or warm compresses. It may be necessary to apply them 20 minutes at a time three to four times daily. Heat application increases circulation to the area and allows the body to fight off the infection by bringing antibodies and white blood cells to the site of infection.
If a boil occurs as a result of shaving, it is recommended to avoid shaving in that area until the boil has healed to avoid the spread of bacteria.
As long as the boil is small and firm, opening the area and draining the boil is not helpful, even if the area is painful. However, once the boil becomes soft or "forms ahead" (that is, a small pustule or area of pus is noted in the boil), it can be ready to drain (lance). Once drained, pain relief can be dramatic. Most small boils, such as those that form around hairs, drain on their own with hot soaks. On occasion, and especially with larger boils, medical treatment is required. In this situation, the boil will need to be drained or "lanced" by a healthcare professional. Frequently, these larger boils contain several pockets of pus that must be opened and drained.
Over-the-counter antibiotics are often used to eliminate any accompanying bacterial infection, especially if there is an infection of the surrounding skin. However, antibiotics are not needed in every situation. Antibiotics have difficulty penetrating the outer wall of an abscess well and often will not cure an abscess without additional surgical drainage.
When an antibiotic is used, the choice depends upon the type of infection that is present as well as the results of tests to identify the precise bacteria that infect the area. Examples of drugs that have been used in the treatment of boils include topical preparations of clindamycin (Cleocin and others), mupirocin (Bactroban), and cephalexin (Keflex).
What is the prognosis (outcome) for a boil?
The majority of boils in healthy people resolve on their own with home care (described above) without forming a scar. The prognosis is also excellent for boils that are treated in the health care setting by opening or lancing. Antibiotics may or may not be required after a boil has been lanced by a healthcare professional. Complications of a boil are rare and are more likely to occur in people with suppressed immune systems.
What are complications of boils?
Complications of boils include the formation of a larger abscess, a worsening or spreading of infection to adjacent areas of skin or soft tissue (cellulitis), and very rarely, the spread of the infection through the bloodstream to sites elsewhere in the body. Sometimes a boil may be caused by an organism typically associated with more serious infections, such as methicillin-resistant Staphylococcus aureus (MRSA), with a risk of spreading this infection to deeper tissues.
Recurrence of the infection is another possible complication, which is more likely in certain types of boils. Recurrence is most common in the disease hidradenitis suppurativa and may also occur in situations in which the cause of the boil or abscess is persistent, such as the clogging of oil ducts seen in cystic acne.
What can people do to prevent boils (abscesses)?
There are some measures that people can take to prevent boils from forming, although boils are not completely preventable. Good hygiene and the regular use of antibacterial soaps can help prevent bacteria from building up on the skin. This can reduce the chance for the hair follicles to become infected and prevent the formation of boils. In some situations, a health care professional may recommend special cleansers such as pHisoderm to even further reduce the bacteria on the skin. When the hair follicles on the back of the arms or around the thighs are continually inflamed, regular use of an abrasive brush (loofah brush) in the shower can be used to help break up oil plugs and buildup around hair follicles.
Pilonidal cysts can be prevented by avoiding continuous direct pressure or irritation of the buttock area when a local hair follicle becomes inflamed. At that point, regular soap and hot water cleaning and drying can be helpful.
For acne and hidradenitis suppurativa (see above), topical or oral antibiotics may be required on a long-term basis to prevent recurrent abscess formation. As mentioned above, surgical resection of sweat glands in the involved skin may be necessary. Other medications, such as isotretinoin (Accutane), can be used for cystic acne and have been helpful in some patients with hidradenitis suppurativa. Recurrences are common in patients with hidradenitis suppurativa.
Finally, surgery may occasionally be needed, especially for pilonidal cysts that recur but also for hidradenitis suppurativa. For pilonidal cysts, surgically removing the outer shell of the cyst is important to clear the boil. The procedure is typically performed in the operating room. For hidradenitis suppurativa, extensive involvement can require surgical repair by a plastic surgeon.
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Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.
Satter, Elizabeth Kline. "Folliculitis." Medscape. May 22, 2018. <http://emedicine.medscape.com/article/1070456-overview>.
Singhal, Hemant. "Skin and Soft Tissue Infections - Incision, Drainage, and Debridement." Medscape. May 10, 2018. <http://emedicine.medscape.com/article/1830144-overview>.
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