Understanding boils

What is a boil?

A boil, also known as a furuncle, is a skin infection affecting hair follicles. Microorganisms cause boils, more specifically Staphylococcus aureus (S. aureus for short). When this pathogen enters damaged skin, it infects hair follicles causing local inflammation and forming firm pus-filled lesions.¹ Boils usually develop in the skin on the armpit, scalp, buttocks, and other areas subject to friction.²

What causes boils?

S. aureus is a normal inhabitant of healthy skin, i.e. part of the skin flora, and under normal conditions does not cause infection. Injuries to the skin surface act as front doors for bacteria like S. aureus to enter through.³ Intact skin is a defensive barrier that keeps out disease-causing microorganisms. Whenever the skin structure is compromised, for example as a result of trauma, chemical burns, insect bites or even just simple friction, pathogens can get to the deeper skin layers and infect nearby structures such as skin follicles.⁴ Soon after that, the immune system starts recognising invading bacteria as invaders and attacks them mercilessly, releasing a plethora of signalling molecules and antibodies leading to inflammation of the affected hair follicle and nearby skin. S. aureus doesn’t just stand idly by but fights back by producing different toxins such as:^5,6,7,8

• Exfoliatin: an enzyme that attacks a specific protein in human skin that is responsible for holding skin cells together. Exfoliatin breaks down this protein and this way loosens up the skin, setting the ground for further infection⁵
• TSST-1, short for toxic shock syndrome toxin-1: is found in up to 25% of all S. aureus isolates. It activates white blood cells making them produce even more signaling molecules, facilitating local inflammation. TSST-1 plays an important role in the systemic complications of boils, as seen below⁶
• PVL, short for Panton-Valentine leukocidin (named after its discoverers - Panton and Valentine: is a toxin that is specialized in destroying white blood cells by punching holes through their cellular membranes causing them to bleed to death. Unlike in TSST-1, PVL-producing S. aureus isolates are pretty rare, being recognized in under 5% of all staphylococcal infections,⁷ as the gene encoding this toxin is derived from a strain of a bacteria-eating virus (i.e. bacteriophage) known as Φ-PVL.⁸ PVL gives a really good ‘kick’ to boil complications and is associated with more severe staphylococcal infections

This battle between the immune system and the invading bacteria leads to the formation of pus - a physiological byproduct of dead white blood cells, dead skin cells, dead bacteria and their metabolites. Small pus-filled lesions such as acne and folliculitis are practically harmless. Pus in boils however is of large quantity and may lead to serious complications.

Typical symptoms

Boils start as swollen, tender and reddish inflamed lumps of the skin that with time build up pus causing them to swell even further; pain in the affected area increases progressively until the pus starts draining on its own, after which the pain slowly starts to go away. In some cases, boils do not shrink and may instead start to build up even more pus leading to worsening of symptoms. Sometimes, a red streak may appear on the skin leading away from the boil. This might mean that the infection has spread to nearby lymph nodes, which is even more apparent when lymph nodes are swollen.⁹

Common complications of boils

Subsequent skin and soft tissue infections

If boils are left untreated, the infection can spread to nearby skin and soft tissues causing different infections:

• Carbuncles – carbuncles are formed from the merging of several closely located boils, i.e. more than one neighbouring hair follicle may be involved in a single infectious process¹⁰
• Abscesses – an abscess can be formed when skin tissue inside a boil dies, leaving necrotic tissue in its place⁹
• Cellulitis – an infection of a portion of the skin and its underlying fat and soft tissues Cellulitis presents as swelling, discolouration, and tenderness of the affected skin¹
• Recurrent boils – boils that reappear as often as three times in a single year are referred to as recurrent boils^11,12

Spread to other organs and systems

S. aureus, especially when producing PVL, is known to cause not only skin but also some life-threatening infections:

• Endocarditis - when S. aureus enters the bloodstream and reaches the heart, it sticks to the heart’s valves and causes inflammation. Inflammation is a risk factor for the development of blood clots that can break apart and lodge into small blood vessels, potentially leading to fatal ischemia of internal organs and death. Not only that but bacteria use formed clots as shuttles to spread to other organs such as the lungs, bones, and brain where they can further facilitate infections.¹³ Staphylococcal endocarditis is one of the most deadly heart diseases with a mortality of 30-40%¹⁴
• Osteomyelitis - staphylococcal infection of the bones may lead to chronic inflammation and formation of bone abscesses, leading to progressive bone destruction and loss of bone density¹⁵
• Pneumonia - a possible complication of infective endocarditis clots that travel to the lungs, cause the formation of pulmonary abscesses and chronic inflammation known as staphylococcal pneumonia^16,17
• Meningitis - if an infected blood clot reaches the blood vessels of the brain, bacteria can cause local inflammation of the linings of the brain (known as the meninges) and formation of brain abscesses. Staphylococcal meningitis is a dangerous complication of S. aureus infections^18,19

Systemic infections

Pus contained in boils is a mixture of pro-inflammatory molecules and bacterial toxins. It’s a ticking time bomb that may lead to severe disease if it leaks into the bloodstream. As discussed above, TSST-1 is a powerful activator of the immune system causing the release of large amounts of pro-inflammatory molecules, leading to sepsis and shock.²⁰ Systemic inflammation in staphylococcal sepsis has been shown in some cases to cause the formation of clots leading to potentially fatal pulmonary embolism.²¹

It is therefore important to not underestimate the severity of skin infections and instead seek medical attention on time to prevent the manifestation of life-threatening complications.

When to seek medical attention

People with boils should seek urgent medical attention in the following cases:²²

• Severe symptoms - in cases of extreme pain and/or swelling in the affected area, rapid growth and formation of necrotic tissue
• Signs and symptoms of systemic infection - fatigue, fever, nausea or vomiting
• Non-healing boils lasting for longer than 2 weeks
• Presence of multiple boils and/or carbuncles
• In case of individuals at high risk of complications - such as elderly people or very young children; people living with diabetes due to impaired wound healing; people with a weakened immune system due to a higher risk of severe infections

Treatment options

Home remedies and care

If the boil does not show alarming growth, tenderness and/or build-up of pus and necrotic tissue, most of the time it can be taken care of with simple home remedies such as warm compresses to help the pus drain naturally and relieve pain; and cleaning the lesion to prevent further bacterial contamination.²³ There is a controversial statement that boils should be cleaned with antibacterial soap instead of plain soap. Given the fact that plain soap has as many antibacterial properties as the ones labelled as ‘antibacterial’, this statement should not be taken seriously which is also supported by the FDA.²⁴

Over-the-counter pain relievers (e.g., paracetamol) and anti-inflammatory agents (e.g., ibuprofen) can have benefits in reducing the uncomfortable sensation that boils cause until the wound has healed.²⁵ Healthcare providers might suggest topical medications that speed up the healing process by draining pus through the skin. Such medication is the ointment containing a drug called ammonium bituminosulfonate.²³

Medical treatment

If boils don’t show signs of healing after 2 weeks, surgical intervention should be performed. In this procedure an incision in the boil is made, allowing the pus to drain out, after which the incision is left open and is only covered with a plaster of compress to leave it to heal on its own.²⁶ This procedure takes about 10-20 minutes²⁷ and has a high success rate of 80%.²⁶

Oftentimes, the treating surgeon might prescribe antibiotics such as trimethoprim-sulfamethoxazole or clindamycin to reduce the risk of secondary infection or recurrence of the boil.²⁸

If there are complications or a high risk of developing such, intravenous antibiotics are typically used. A group of antibiotics known as antistaphylococcal penicillins (nafcillin, cloxacillin, dicloxacillin, and flucloxacillin) were used in the past to effectively combat S. aureus infections, despite the latter producing specific enzymes that break down penicillins (known as penicillinases).²⁹ Today however a concerning number of cases of multi-drug resistant S. aureus known as MRSA (methicillin-resistant S. aureus) have emerged. MRSA are resistant to all beta-lactam antibiotics (including penicillins, cephalosporins, monobactams, and carbapenems) due to a change in the structure of the drug target of beta-lactam antibiotics.³⁰ MRSA are not only resistant to multiple antibiotics, but also cause more aggressive infections as they are more likely to produce the aforementioned toxin PVL.³¹ Complicated MRSA infections like osteomyelitis and endocarditis are commonly treated with intravenous vancomycin - a glycopeptide antibiotic.³²

Tips to prevent boils

• Proper hygiene - regular washing, avoiding the sharing of clothes and towels, and wearing cotton clothing
• Skincare - dry skin should be regularly moisturised to prevent the formation of cracks through which bacteria can enter. Skin wounds should be cleaned with soap and water and applied topical antibacterial products to prevent infection with S. aureus
• Lifestyle changes - people with underlying conditions like diabetes should manage their symptoms with a healthy diet, exercising, and boosting their immune system³³

Summary

Boils are painful skin infections caused by Staphylococcus aureus, typically affecting hair follicles and leading to pus-filled lesions. They often occur in areas with friction, like the armpits, buttocks, or scalp. While boils can usually be treated with home remedies like warm compresses, severe cases may require medical attention, especially if symptoms worsen or systemic infections develop. Complications can include the spread of infection to other skin areas, organs, or bones, and potentially life-threatening conditions like endocarditis or pneumonia. People should seek medical help if boils don't heal after two weeks if multiple boils or carbuncles appear, or if there are signs of systemic infection (fever, nausea, or fatigue). Treatment may involve drainage, antibiotics, or surgical intervention. Prevention includes proper hygiene, wound care, and managing underlying health conditions like diabetes.