A boil is a painful, red bump on the skin usually caused by an infected hair follicle (a small sac in the skin that a hair grows out of).
As white blood cells fight the infection, pus forms inside and the boil grows larger. Eventually, it will rupture (burst) and the pus will drain away.
Boils usually occur on the neck, face, thighs, armpits and buttocks.
How common are boils?
Boils are common among teenagers and young adults. People with a weakened immune system are also more likely to get boils.
Treating boils
Most boils will heal without the need for treatment within two weeks.
Antibiotics are usually only needed if there are complications, such as the infection spreading into a deeper layer of skin (cellulitis).
Continue to next section: Symptoms of boils