|Classification and external resources|
A boil, also called a furuncle, is a deep folliculitis, infection of the hair follicle. It is most commonly caused by infection by the bacterium Staphylococcus aureus, resulting in a painful swollen area on the skin caused by an accumulation of pus and dead tissue. Individual boils clustered together are called carbuncles. Most human infections are caused by coagulase-positive S. aureus strains, notable for the bacteria's ability to produce coagulase, an enzyme that can clot blood. Almost any organ system can be infected by S. aureus.
Signs and issues 
Boils are bumpy, red, pus-filled lumps around a hair follicle that are tender, warm, and very painful. They range from pea-sized to golf ball-sized. A yellow or white point at the center of the lump can be seen when the boil is ready to drain or discharge pus. In a severe infection, an individual may experience fever, swollen lymph nodes, and fatigue. A recurring boil is called chronic furunculosis. Skin infections tend to be recurrent in many patients and often spread to other family members. Systemic factors that lower resistance commonly are detectable, including: diabetes, obesity, and hematologic disorders.
Usually, the cause is bacteria such as staphylococci that are present on the skin. Bacterial colonization begins in the hair follicles and can cause local cellulitis and inflammation. Additionally, myiasis caused by the Tumbu fly in Africa usually presents with cutaneous furuncles. Risk factors for furunculosis include bacterial carriage in the nostrils, diabetes mellitus, obesity, lymphoproliferative neoplasms, malnutrition, and use of immunosuppressive drugs. Patients with recurrent boils are as well more likely to have a positive family history, take antibiotics, and to have been hospitalized, anemic, or diabetic; they are also more likely to have associated skin diseases and multiple lesions.
The most common complications of boils are scarring and infection or abscess of the skin, spinal cord, brain, kidneys, or other organs. Infections may also spread to the bloodstream (bacteremia) and become life-threatening. S. aureus strains first infect the skin and its structures (for example, sebaceous glands, hair follicles) or invade damaged skin (cuts, abrasions). Sometimes the infections are relatively limited (such as a stye, boil, furuncle, or carbuncle), but other times they may spread to other skin areas (causing cellulitis, folliculitis, or impetigo). Unfortunately, these bacteria can reach the bloodstream (bacteremia) and end up in many different body sites, causing infections (wound infections, abscesses, osteomyelitis, endocarditis, pneumonia) that may severely harm or kill the infected person. S. aureus strains also produce enzymes and exotoxins that likely cause or increase the severity of certain diseases. Such diseases include food poisoning, septic shock, toxic shock syndrome, and scalded skin syndrome. Almost any organ system can be infected by S. aureus.
A small boil may burst and drain on its own without any assistance. In some instances, however, draining can be encouraged by application of a cloth soaked in warm salt water. Washing and covering the furuncle with antibiotic cream or antiseptic tea tree oil and a bandage also promotes healing.
Furuncles at risk of leading to serious complications should be incised and drained by a medical practitioner. These include furuncles that are unusually large, last longer than two weeks, or are located in the middle of the face or near the spine. Fever and chills are signs of sepsis that require immediate treatment. 
Antibiotic therapy is advisable for large or recurrent boils or those that occur in sensitive areas (such as around or in the nostrils or in the ear). Staphylococcus aureus has the ability to acquire antimicrobial resistance easily, making treatment difficult. Knowledge of the antimicrobial resistance of S. aureus is important in the selection of antimicrobials for treatment. Poor personal hygiene being common, the role of nasal S. aureus carrier may differ from communities with good hygienic practices. Staphylococcus aureus re-infection may result from contact with infected family members, contaminated fomites, or from other extra-nasal sites. This raises a suggestion to treat household contacts and close contacts if recurrence persists, because it is likely that one or more contacts are asymptomatic carriers of S. aureus. In addition to the increase in the cost of treatment in poor countries, the possibility of developing drug resistance must be considered. The most important independent predictor of recurrence is a positive family history. Boils are spread among individuals by touching or bursting a boil. Furunculosis is a common disease, particularly with deficient hygiene. A large number of S. aureus organisms are frequently present on the sheets and underclothing of patients with furunculosis and may cause re-infection of patients and infection of other members of the family. The role of iron deficiency anemia in recurrent furunculosis was demonstrated, all patients were free from recurrence during the six months follow-up period after iron supplementation. A variety of host factors, such as abnormal neutrophil chemotaxis, deficient intra-cellular killing, and immuno-deficient states are of importance in a minority of patients with recurrent furunculosis. Health education about sound personal hygiene and correction of anemia should be mandatory in management of furunculosis. It was found that recurrence was significantly associated with poor personal hygiene. A previous study reported that MRSA infection was significantly associated with poor personal hygiene. It was reported that frequent hand and body washing with water and antimicrobial soap solution decreases staphylococcus skin colonization. Previous use of antibiotics is associated with a high risk of recurrence. This may be due to the development of resistance to the antibiotics used. An associated skin disease favors recurrence. This may be attributed to the persistent colonization of abnormal skin with S. aureus strains, such as is the case in patients with atopic dermatitis.
In popular culture 
- In Exodus 9:8–12, the 6th Plague of Egypt was the Plague of boils.
- In the 2010 film Legion, one of the diner patrons is found crucified upside down and covered with huge boils.
See also 
- MedlinePlus Encyclopedia Furuncle
- MedlinePlus Encyclopedia Carbuncle
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