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Boils

 

A boil is a red, painful, lump on the skin that develops at the site of an infected hair follicle. A hair follicle is a small sac in the skin that a hair grows out of.

As white blood cells fight the infection, pus forms inside the boil and the boil grows larger and becomes more painful. Eventually, it will burst and the pus will drain away. This can take from two days to three weeks to happen.

A carbuncle is a collection of boils that develop in a group of hair follicles under the skin.

Read more about the symptoms of boils and carbuncles.

Causes of boils and carbuncles

Boils and carbuncles are caused by a type of bacteria known as staphylococcus aureus (staph bacteria). Staph bacteria usually live harmlessly on the surface of the skin or in the lining of the nose. However, if they get inside the skin, they can trigger skin infections, such as boils.

Read more about the causes of boils and carbuncles.

Who is affected by boils and carbuncles?

Boils are relatively common in teenagers and young adults, usually in males. Young males living in over-crowded and possibly unhygienic conditions, such as a military base or prison, are particularly at risk (see box, left).

Carbuncles are less common and tend to occur mostly in middle-aged or older men who are in poor health due to a pre-existing health condition, such as heart disease.

Read more about the causes and risk factors for boils and carbuncles.

When to see your GP

Most boils burst and heal by themselves without the need for medical treatment. However, you should visit your GP if you have a boil:

  • on your face or nose
  • that gets bigger and feels soft and spongy to touch (it may not burst and heal by itself)
  • that doesn't heal within two weeks

Treating boils

You should be able to successfully treat a boil at home. One of the best ways to speed up healing is to apply a warm facecloth to the boil, three or four times a day.

If your boil doesn't heal, your GP may decide to drain it.

Never attempt to squeeze or pierce a boil or carbuncle because it could cause the infection to spread and may lead to complications (see below).

Carbuncles are usually treated with a course of antibiotics. 

Complications

Boils and carbuncles can cause secondary infections.

This can range from a relatively minor (though often very painful) infection of the deeper layer of the skin, such as cellulitis, to rarer more serious infections, such as blood poisoning (sepsis).

Boils around the nose or eyes can spread to the brain and cause serious injury.

Larger boils and carbuncles can also lead to scarring, particularly if they're not treated by a properly qualified healthcare professional.

Read more about the complications of boils and carbuncles.

Can I catch a boil or carbuncle?

Yes you can. Unlike acne both boils and carbuncles can spread to another part of the body or to another person. This is because the pus contained in boils and carbuncles carries the staph bacteria.

Taking some simple precautions, such as carefully disposing of used dressings and washing your hands after touching affected areas of skin, can help to prevent boils and carbuncles from spreading.

Boils

Boils can develop anywhere on your skin, but they're most likely to occur in places where there's a combination of growing hair, friction and sweat, such as the:

  • neck
  • face
  • thighs
  • armpits
  • buttocks

Boils can be single or develop in clusters. When a boil first forms, it will appear as a swollen, painful red lump that's similar in size to a twenty cent coin. Over the next few days, the boil will begin to grow.

The size of boils can vary significantly. Some boils can grow to the size of a golf ball. Yellowish-white coloured pus will begin to build up at the centre or tip of the boil. However, it's very important to resist the urge to squeeze the boil because it could lead to more serious complications.

Eventually, the boil will usually burst open and the pus will drain away, leaving your skin to heal. This can take from two days to three weeks to happen. Most boils don't leave any scarring unless they're particularly large.

Carbuncles

A carbuncle is a red, hard painful lump that grows over the space of a few days. It usually develops on the back of the neck, the back or thighs.

A fully grown carbuncle can range in size from 3cm (1.1 inches) to over 10cm (4 inches), and will leak pus from a number of points. You may also have additional symptoms, such as:

  • a high temperature of 38ºC (100.4ºF) or above
  • a general feeling of being unwell and 'out of sorts'
  • feeling weak and exhausted

When to seek medical advice

Contact your GP for advice if you have:

  • a moderate to large boil that feels soft and spongy to the touch
  • a carbuncle
  • a boil on your face - this can sometimes cause serious complications
  • additional symptoms, such as a high temperature or feeling generally unwell
  • a secondary infection, such as cellulitis (an infection of the deeper layer of the skin)
  • a boil and a health condition that's known to weaken the immune system, such as type 2 diabetes or HIV or AIDS
  • a boil and you're receiving medical treatment that's known to weaken the immune system, such as chemotherapy
  • a boil that shows no sign of healing after two weeks
Pain
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
Swelling
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

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
Bacteria
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease but some others are good for you.
Immune system
This is the body's defence system, which helps protect it from disease, bacteria and viruses.
Obese
Obesity is when a person has an abnormally high amount of body fat.

Your GP will be able to diagnose a boil or carbuncle by looking at it. Further testing is usually only required if you have:

  • a boil or carbuncle that doesn't respond to treatment; it may be caused by bacteria other than staph bacteria
  • multiple boils or carbuncles
  • a weakened immune system, due to a condition, such as diabetes, or you're having a treatment, such as chemotherapy

In these circumstances, your GP will probably use a cotton swab to take a tissue sample from the boil so that it can be examined under a microscope.

You may also be referred for a blood test to see if you have an underlying health condition, such as diabetes (if diabetes hasn't previously been diagnosed), which could be increasing your risk of developing boils and carbuncles.

Self care

In most cases, boils can be treated successfully at home. One of the best ways to speed up the healing process is to apply a warm facecloth to the boil for 10 minutes, three or four times a day. The heat increases the amount of blood circulating around the boil, which means more infection-fighting white blood cells are sent there.

After the boil has burst, cover it with a sterile gauze or dressing to prevent the spread of infection. Wash your hands thoroughly using hot water and soap because this will help to prevent you from spreading any bacteria to other parts of your body or to other people.

Over-the-counter painkillers, such as paracetamol or ibuprofen, can relieve any pain caused by the boil.

Larger boils

See your GP if you have a larger boil that feels soft and spongy to the touch (the medical name for this is a fluctuant boil).

Once a boil becomes soft and spongy, it is unlikely to burst open by itself and probably won't respond well to treatment with antibiotics. Your GP may be able to remove the pus using a technique called incision and drainage. In some cases, your GP may refer you to your local hospital for this treatment.

Incision and drainage involves piercing the tip of the boil with a sterile needle or scalpel. This encourages the pus to drain out of the boil, which should help to relieve pain and stimulate the recovery process. Before having the procedure you're likely to be given a local anaesthetic to numb the affected area.
 
Never attempt to squeeze or pierce the head of a boil yourself because this can spread the infection.

When antibiotics are required

Antibiotics are usually recommended:

  • for all cases of carbuncles
  • if you have a high temperature
  • if you develop a secondary infection, such as cellulitis (an infection of the deeper layer of the skin)
  • if you have a boil on your face; facial boils have a higher risk of causing complications
  • if you're in severe pain and discomfort

A seven-day course of an antibiotic called flucloxacillin is usually recommended.

These side effects are usually mild and should pass once your course of antibiotics has finished.

Antibiotics
Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin.
Antiseptic
Antiseptic is a substance that reduces the growth and development of germs.
Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.

Scarring

Scarring can sometimes occur following a larger boil or carbuncle. While scars never disappear completely, they do fade with time and become less noticeable.

If you're particularly concerned about scars, there are a number of treatment options, including:

  • corticosteroid injections, which can help to flatten a raised scar
  • medications, such as aminobenzoate, which help to break down scar tissue
  • pressure dressings - these help to flatten and soften a scar 
  • plastic surgery

A simpler alternative is to use make-up to conceal any scars that you have. Camouflage make-up that's specially designed for covering up scars is available over the counter at pharmacies.

Read more about treating scars.

Spread of infection

The bacteria inside a boil or carbuncle can sometimes spread to other parts of the body and trigger a secondary infection.

Cellulitis is the most common secondary infection associated with boils and carbuncles. Cellulitis is an infection of the deeper layers of the skin.

See Cellulitis for more information.

Much less common secondary infections associated with boils and carbuncles include:

  • septic arthritis - an infection of a joint
  • osteomyelitis - an infection that develops inside a bone
  • endocarditis - an infection of the inner layer of the heart
  • septicaemia - an infection of the blood
  • brain abscess - a collection of pus develops inside the brain

These less common secondary infections need to be treated with injections of antibiotics. In the case of septicaemia and brain abscess, admission to an intensive care unit (ICU) may be required.

Cavernous sinus thrombosis

Cavernous sinus thrombosis is very rare but potentially life-threatening complication of a boil. It occurs when an infection triggers a blood clot in the spaces behind the eye socket and the clot begins to increase pressure on the brain, causing symptoms such as:

  • a sharp and severe headache
  • swelling of the eyes
  • eye pain that's often severe

Without prompt treatment with antibiotics, cavernous sinus thrombosis can be fatal. However, it should be stressed that only 1 in every 2.5 million people in Ireland will develop this complication in any given year.

Bacteria
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease but some others are good for you.
Lesion
A lesion is an abnormal change in an organ or body tissue because of injury or disease.
Swellings
Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.
Tissue
Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, or storing fat.

It's not always possible to prevent getting a boil or carbuncle, particularly if you have a weak immune system (the body's natural defence against infection and illness).

However, the advice listed below should help.

  • Wash your skin regularly, using a mild anti-bacterial soap.
  • Always carefully clean any cuts, wounds or grazes, even if they look very small.
  • Keep cuts, wounds and grazes covered with a sterile bandage until they heal.
  • Eat a healthy diet and take regular exercise to boost your immune system; this will make you less likely to develop skin infections, such as boils.

Preventing your boil or carbuncle from spreading

If you develop a boil or carbuncle, it's important to take a number of steps to prevent spreading the infection to other parts of your body or to other people:

  • Wash your hands with an anti-bacterial soap after touching a boil or carbuncle.
  • Wash underwear, bed linen and towels at a high temperature.
  • Use a separate facecloth and towel.
  • Keep any wounds covered with sterile gauze until they heal.
  • Regularly change the gauze covering a boil or carbuncle.
  • Used gauze or dressings should be sealed in a plastic bag and immediately thrown away in the dustbin.
Antiseptic
Antiseptic is a substance that reduces the growth and development of germs.
Bacteria
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease but some others are good for you.
Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.