Boils
Most boils are caused when staphylococcus aureus, also known as staph bacteria, infect one or more hair follicles (a follicle is a sac in the skin that a hair grows out of). Staph bacteria are commonly found on the skin and inside the nose and throat.
The skin usually provides a robust defence against bacteria. However, it's sometimes possible for staph bacteria to enter the skin through a cut or graze. When bacteria infect your skin, your immune system responds by sending infection-fighting white blood cells to the source of the infection, to kill the bacteria.
Over time, a mix of dead bacteria, dead white blood cells and dead skin cells builds up inside the boil. This is known as pus.
Who’s at risk
Known risk factors (things that make you more likely to get boils) include:
- being male (particularly a teenage boy) – this could be because the hormonal changes during puberty can make the skin greasy, which may encourage the growth of bacteria
- being in close personal contact with someone who has a boil
- taking part in sports that involve a combination of close personal contact and frequent friction to the skin, such as rugby and wrestling
- living in conditions that are overcrowded and/or have poor standards of personal hygiene
- having a pre-existing skin condition, such as atopic eczema or scabies
- obesity – being very overweight with a body mass index (BMI) of 30 or above
Carbuncles
Like boils, carbuncles are also caused by staphylococcus aureus bacteria. A carbuncle develops when the infection that causes a single boil spreads beneath the skin to create a cluster of boils.
People who are in poor health or those with a very weak immune system (the body’s natural defence against infection and illness) are thought to be most at risk of developing a carbuncle. These include people:
- with diabetes – high sugar levels in the blood make it more difficult for your immune system to protect you against skin infection
- with health conditions known to weaken the immune system, such as HIV
- who are on a long-term course of steroid tablets or injections (corticosteroids) – long-term steroid use makes you more vulnerable to infection
- who are having treatment known to weaken the immune system, such as chemotherapy
- who are malnourished (not getting the nutrients needed from food to maintain good health)
- with skin conditions that affect a large part of their body, such as more severe forms of psoriasis
- with heart failure
- with a severe drug misuse problem, particularly those who inject drugs
