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A boil is a red, painful, pus-filled swelling of the skin caused by a bacterial infection.
A boil develops when a hair follicle or sebaceous gland (which secretes sebum into the hair follicle) becomes infected. The infection then spreads and pus collects in surrounding tissues. Common sites for boils are moist areas, such as the groin, or areas where friction occurs, such as under a collar. Boils are usually due to infection with the bacterium Staphylococcus aureus, which some people normally carry on the skin or in the nose without symptoms. A cluster of connected boils is called a carbuncle.
Boils are most common in people whose resistance to infection is lowered by a disorder such as diabetes mellitus or AIDS (see Hiv infection and aids), but they can occur in those without immune problems.
What are the symptoms of a boil?
The symptoms develop gradually in the following order over several days:
- A small, red lump appears.
- The area becomes painful and tender.
- The lump and the tissues around it begin to swell as pus accumulates.
- A white or yellow head of pus appears at the centre of the boil.
- The affected area feels warm to the touch and throbs.
Boils often clear up without treatment. They may burst and release the pus or gradually subside and then disappear.
What can I do?
You can relieve pain and help the healing process by applying a cotton-wool ball or a clean cloth soaked in hot water to the area for about 30 minutes four times a day. Do not squeeze the boil because this may cause the infection to spread further. If a boil does not start to heal within a few days or it becomes large or painful, consult your doctor.
What might the doctor do?
Your doctor may drain the pus in the swelling by making a small incision in the centre of the boil with a sterile needle. You may also be prescribed oral antibiotics to treat the cause of the infection. Large boils may need to be lanced with a surgical knife under local anaesthesia.
If you develop recurrent boils, you may have blood and urine tests to look for an underlying disorder. Your doctor may also recommend that you use antiseptic soap or cream to kill the bacteria (see Preparations for skin infections and infestations).
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