A boil is a painful, pus-filled bump that forms under your skin when bacteria infect a hair follicle. It looks like a swollen red lump that grows over several days, eventually developing a white or yellow center as pus collects inside. Boils are extremely common and usually resolve on their own, but larger or more stubborn ones sometimes need medical attention.
What Causes a Boil
Most boils are caused by Staphylococcus aureus, a bacterium that naturally lives on your skin and inside your nose. Under normal circumstances, it’s harmless. But when it finds a way beneath the skin’s surface, typically through a small cut, insect bite, or irritated hair follicle, it can trigger an infection. Your immune system responds by sending white blood cells to the area, and the resulting battle produces pus, swelling, and pain.
Boils tend to show up in areas where skin rubs together or where you sweat heavily: the inner thighs, armpits, groin, buttocks, and along the waistline. They can also appear on the face or neck, especially around the beard area where shaving creates tiny nicks. People with weakened immune systems, diabetes, or skin conditions like eczema are more prone to developing them, but anyone can get a boil.
How a Boil Develops
A boil usually forms over a few hours to a few days. It starts as a tender, swollen red bump, often smaller than a pencil eraser. At this early stage, it can look a lot like a large pimple. Over the next several days, the bump fills with pus, becoming increasingly painful. The area may itch before the boil fully forms, and the skin around it often turns red and shiny as it stretches.
As the boil matures, a yellow or white tip appears at the center, similar to a pimple’s head. The bump may feel firm or slightly squishy depending on how much pus has accumulated. Some boils grow as large as a golf ball. Eventually, if left alone, a boil will break open and drain on its own. During this process, it may ooze or crust over as the body clears the infection.
Boils vs. Cysts and Pimples
Boils are easy to confuse with cysts and cystic acne, but a few key differences help tell them apart. A boil grows rapidly, is usually painful from the start, and feels warm to the touch. A cyst, by contrast, is a smooth, round sac under the skin filled with fluid or semisolid material. Cysts grow slowly, feel movable when you press on them, and typically aren’t painful unless they become inflamed.
Pimples and boils can look identical in the early stages, but boils grow much larger and hurt significantly more. A regular pimple rarely exceeds a few millimeters, while a boil can swell to 2 inches or more across. The pain also tends to be deeper with a boil because the infection sits farther beneath the skin’s surface, rooted in the hair follicle rather than in a superficial pore.
Treating a Boil at Home
The most effective home treatment is a warm compress. Soak a clean washcloth in warm water, wring it out, and hold it against the boil for about 10 minutes at a time, several times a day. The heat increases blood flow to the area, helps your body fight the infection, and encourages the boil to come to a head and drain naturally. You can repeat this throughout the day whenever it’s convenient.
Keep the area clean with mild soap and water, and cover a draining boil with a loose bandage to prevent the pus from spreading bacteria to other parts of your skin. Resist the urge to squeeze or lance the boil yourself. Squeezing can push the infection deeper into surrounding tissue, and using a needle at home introduces a serious risk of spreading bacteria or causing a secondary infection. Once the boil drains on its own, continue applying warm compresses until it fully heals.
When a Boil Needs Medical Care
Most small boils heal without professional help, but certain signs warrant a visit to a doctor. A boil larger than 2 inches (about 5 cm) across often needs to be drained in a clinical setting. The same applies if the boil sits on your face, since infections there can spread more easily to surrounding structures. A red rash spreading outward from the boil, or a fever developing alongside it, suggests the infection may be moving beyond the skin and into your bloodstream.
You should also seek care if a boil hasn’t improved after a few days of warm compresses, if you develop multiple boils at once, or if you have a condition that weakens your immune system. For children under one year old, any boil is worth having checked.
When a doctor drains a boil, the procedure is straightforward. After numbing the area with a local anesthetic, the doctor makes a small incision to let the pus escape, then cleans out the cavity. The wound is covered with absorbent gauze, and you’ll typically return for a follow-up within a day or two. At home, you’ll continue warm soaks and dressing changes every one to two days until the wound fills in with healthy tissue and stops draining.
When One Boil Becomes Several
Sometimes a cluster of boils forms when the infection spreads to multiple nearby hair follicles. This cluster is called a carbuncle, and it’s essentially several boils joined together beneath the skin. Carbuncles are deeper, more painful, and more likely to cause fever or general fatigue than a single boil. They’re also more common in people with diabetes or compromised immune systems.
Recurring boils can happen when staph bacteria colonize a particular area of skin or the inside of the nose. If you keep getting boils in the same spot or develop them frequently, a doctor may test for antibiotic-resistant strains and recommend a treatment plan to reduce the bacteria living on your skin. Simple steps like washing towels and bedsheets frequently, avoiding sharing razors, and keeping skin folds dry can help prevent boils from coming back.