A boil, also called a furuncle, is a deep folliculitis, which is an

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...

of the hair follicle. It is most commonly caused by infection by the

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...

'' Staphylococcus aureus'', resulting in a painful swollen area on the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...

caused by an accumulation of pus and dead tissue. Boils which are expanded are basically pus-filled nodules. Individual boils clustered together are called

carbuncle A carbuncle is a cluster of boils caused by bacterial infection, most commonly with ''Staphylococcus aureus'' or ''Streptococcus pyogenes''. The presence of a carbuncle is a sign that the immune system is active and fighting the infection. The ...

s. Most human infections are caused by coagulase-positive ''S. aureus'' strains, notable for the bacteria's ability to produce

coagulase Coagulase is a protein enzyme produced by several microorganisms that enables the conversion of fibrinogen to fibrin. In the laboratory, it is used to distinguish between different types of ''Staphylococcus'' isolates. Importantly, '' S. aureus'' ...

, an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that can clot blood. Almost any

organ system An organ system is a biological system consisting of a group of organs that work together to perform one or more functions. Each organ has a specialized role in a plant or animal body, and is made up of distinct tissues. Plants Plants have ...

can be infected by ''S. aureus''.

Signs and symptoms

Boils are bumpy, red, pus-filled lumps around a hair follicle that are tender, warm, and 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 Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

, 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 Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

, and hematologic disorders. Boils can be caused by other skin conditions that cause the person to scratch and damage the skin. Boils may appear on the buttocks or near the anus, the back, the neck, the stomach, the chest, the arms or legs, or even in the ear canal. Boils may also appear around the eye, where they are called

stye A stye, also known as a hordeolum, is a bacterial infection of an oil gland in the eyelid. This results in a red tender bump at the edge of the eyelid. The outside or the inside of the eyelid can be affected. The cause of a stye is usually a b ...

s. A boil on the gum is called

intraoral dental sinus Intraoral dental sinus (also termed a parulis and commonly, a gumboil) is an oral lesion characterized by a soft erythematous papule (red spot) that develops on the alveolar process in association with a non-vital tooth and accompanying dental abs ...

, or more commonly, a gumboil.

Complications

The most common complications of boils are

scarring A scar (or scar tissue) is an area of fibrous tissue that replaces normal skin after an injury. Scars result from the biological process of wound repair in the skin, as well as in other organs, and tissues of the body. Thus, scarring is a na ...

and

or abscess of the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

s, 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 gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest nu ...

s, hair follicles) or invade damaged skin (cuts, abrasions). Sometimes the infections are relatively limited (such as a

, boil, furuncle, or carbuncle), but other times they may spread to other skin areas (causing

cellulitis Cellulitis is usually a bacterial infection involving the inner layers of the skin. It specifically affects the dermis and subcutaneous fat. Signs and symptoms include an area of redness which increases in size over a few days. The borders of ...

, folliculitis, or

impetigo Impetigo is a bacterial infection that involves the superficial skin. The most common presentation is yellowish crusts on the face, arms, or legs. Less commonly there may be large blisters which affect the groin or armpits. The lesions may be pa ...

). Unfortunately, these bacteria can reach the bloodstream ( bacteremia) and end up in many different body sites, causing infections (wound infections, abscesses,

osteomyelitis Osteomyelitis (OM) is an infection of bone. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The long bones of the arms and legs are most commonly involved in children e.g. the femur and humerus, while the ...

endocarditis Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves. Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or the ...

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...

) 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 Toxic shock syndrome (TSS) is a condition caused by bacterial toxins. Symptoms may include fever, rash, skin peeling, and low blood pressure. There may also be symptoms related to the specific underlying infection such as mastitis, osteomyeli ...

, and scalded skin syndrome. Almost any organ system can be infected by ''S. aureus''. Squeezing or cutting boils in the danger triangle of the face can be particularly dangerous if done outside a medical setting, as blood vessels in this area drain into the brain and can carry serious infections there. When a boil bursts, a seemingly solid, whitish colored pus initially appears then the pus and some blood follows.

Causes

Bacteria

Naturally the cause is bacteria such as

staphylococci ''Staphylococcus'' is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillales. Under the microscope, they appear spherical ( cocci), and form in grape-like clusters. ''Staphylococcus'' species are facultati ...

that are present on the skin. Bacterial colonisation begins in the hair follicles and can cause local

and inflammation.

Myiasis Myiasis is the parasitic infestation of the body of a live animal by fly larvae (maggots) which grow inside the host while feeding on its tissue. Although flies are most commonly attracted to open wounds and urine- or feces-soaked fur, some spe ...

caused by the tumbu fly in Africa usually presents with cutaneous furuncles.

Risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often ...

s for furunculosis include

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

l carriage in the nostrils,

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

, lymphoproliferative

neoplasm A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues ...

, and use of immunosuppressive drugs.

Family history

People with recurrent boils are as well more likely to have a positive family history, take antibiotics, and to have been hospitalised, anemic, or diabetic; they are also more likely to have associated skin diseases and multiple lesions.

Other

Other causes include poor immune system function such as from

HIV/AIDS Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. Following initial infection an individual ...

, or

alcoholism Alcoholism is, broadly, any drinking of alcohol that results in significant mental or physical health problems. Because there is disagreement on the definition of the word ''alcoholism'', it is not a recognized diagnostic entity. Predomi ...

. Poor hygiene and

have also been linked. It may occur following antibiotic use 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 persons with atopic dermatitis. Boils which recur under the arm, breast or in the groin area may be associated with hidradenitis suppurativa (HS).

Diagnosis

Diagnosis is made through clinical evaluation by a physician, which may include culturing of the lesion.

Treatment

A boil may clear up on its own without bursting, but more often it will need to be opened and drained. This will usually happen spontaneously within two weeks. Regular application of a warm moist compress, both before and after a boil opens, can help speed healing. The area must be kept clean, hands washed after touching it, and any dressings disposed of carefully, in order to avoid spreading the bacteria. A doctor may cut open or "

lance A lance is a spear designed to be used by a mounted warrior or cavalry soldier (lancer). In ancient and medieval warfare, it evolved into the leading weapon in cavalry charges, and was unsuited for throwing or for repeated thrusting, unlike s ...

" a boil to allow it to drain, but squeezing or cutting should not be attempted at home, as this may further spread the infection. Antibiotic therapy may be recommended for large or recurrent boils or those that occur in sensitive areas (such as the groin, breasts, armpits, around or in the nostrils, or in the ear). An antibiotic should not be used for longer than one month, with at least two months (preferably longer) between uses, otherwise it will lose its effectiveness. If the patient has chronic (more than two years) boils, removal by

plastic surgery Plastic surgery is a surgical specialty involving the restoration, reconstruction or alteration of the human body. It can be divided into two main categories: reconstructive surgery and cosmetic surgery. Reconstructive surgery includes cranio ...

may be indicated. Furuncles at risk of leading to serious complications should be incised and drained if antibiotics or steroid injections are not effective. These include furuncles that are unusually large, last longer than two weeks, or occur in the middle of the face or near the spine. Fever and chills are signs of

sepsis Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...

and indicate immediate treatment . ''Staphylococcus aureus'' has the ability to acquire

antimicrobial resistance Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. P ...

easily, making treatment difficult. Knowledge of the antimicrobial resistance of ''S. aureus'' is important in the selection of antimicrobials for treatment.

References

External links

* {{Authority control Bacterium-related cutaneous conditions