An underarm boil, also called a furuncle, forms when bacteria infects a hair follicle. Staphylococcus aureus, which live on the skin, usually cause the infection, though another type of bacteria may be to blame as well. A boil may not need any treatment and may clear up on its own, though most fill with pus, which can be painful and requires treatment.
You can place a warm compress, such as a washcloth dampened with hot water, onto the boil. The warmth of the compress will encourage the boil to burst and the pus to drain, which causes it to heal. You should apply the compress several times a day until the pus drains.
Always wash the compress after using it and do not reuse until it has been cleaned. Wash your hands and the affected area thoroughly, especially after the boil begins to drain. Although popping the underarm boil like a pimple may be tempting, you should avoid doing so, as the pus from the blister can spread onto your skin, leading to more boils.
If the underarm boil is very large or does not clear up after several weeks, you may need to see a doctor to treat it. The doctor will make a small cut into the base of the boil so that the pus will drain. If the boil is large enough, the doctor may have to pack it with gauze so that it can continue to drain into the gauze after you leave the doctor's office. You may need to change the gauze and should be very careful when doing so. Throw the gauze away so that the pus and bacteria from the boil are on the inside. Wash your hands well afterward.
You may need a course of antibiotics for a large underarm boil or for a boil that recurs on other areas of the body. If MRSA, a resistant type of staph, is the cause of the boil, you will definitely need to take antibiotics. Even if the boil clears up or you feel better, take the entire course prescribed by your doctor.
Once the boil has fully drained and gone away, you can take steps to prevent a second boil from forming. Use the hottest water possible to wash your sheets and any clothing worn when you had the boil and your towels. Don't share items such as your razor with friends. If you cut your underarm when shaving, use an antibiotic cream to clean it and apply a bandage to protect it.
