A sudden, painful, pus-filled bump on your skin can be more than just a pimple. Sometimes only one appears, but other times, several form together in the same area. If a few bumps show up close together, it’s called a carbuncle. They can swell, become discolored, and leak fluid.

Many people think boils or carbuncles are a sign of a skin infection. Infections are the most common cause of boils and carbuncles. If these lumps keep coming back — especially in your groin, buttocks, and armpits — they could be a sign of a long-term skin condition that affects the sweat glands. It’s called hidradenitis suppurativa (HS).

Boils vs. Carbuncles

Boils and carbuncles both involve painful and often inflamed bumps on your skin. They can appear anywhere but most often develop on the face, armpits, buttocks, thighs, or back of the neck.

What Does a Boil Look Like?

A boil is a single, pus-filled bump that forms when one or more of your hair follicles become inflamed. It often starts as a small discolored spot that feels tender to the touch, then grows larger as it fills with pus. As it develops, a white or yellow tip can appear at the top, much like a pimple.

The larger it grows, the more painful a boil becomes. Eventually, a boil may burst on its own, causing pus or fluid to drain out of it.

What Does a Carbuncle Look Like?

A carbuncle is a cluster of several boils in a single area. It usually involves an infection of several hair follicles and is filled with pus and dead tissue. The infection can go deeper into the skin than a single boil, and while some carbuncles rupture on their own, others need to be drained by a doctor. Even after a carbuncle is treated and drained, a scar may be left behind.

Because a carbuncle goes deeper into the skin, you might also have symptoms like fever or chills.

Common Causes of Boils and Carbuncles

Risk factors for boils and carbuncles include a weakened immune system, diabetes, skin conditions, skin that’s not kept clean, or generally poor health. Rubbing from tight clothing or shaving can also raise your risk. Other causes may involve underlying conditions, including those listed below.

Infections

The most common cause of boils and carbuncles is an infection with a type of bacteria called Staphylococcus aureus (often shortened to S. aureus or just “staph”). S. aureus is a type of bacteria that lives on your skin, especially in your nose and around your genitals. Some types of staph, like MRSA (methicillin-resistant Staphylococcus aureus), are harder to treat. Staph bacteria can get into your skin through an opening, like an insect bite or injury, and cause an infection.

Staph infections can be contagious, especially through direct contact with infected fluid or shared personal items.

Hidradenitis Suppurativa

HS is a chronic (long-term) inflammatory skin condition that can cause you to repeatedly develop boils on parts of your body with sweat glands, like in your armpits, under your breasts, or in your groin. A tender or painful bump under the skin, which later becomes a boil, may be an early symptom of HS.

With HS, these boils can become pus-filled abscesses even when there isn’t an infection. HS boils can look a lot like staph infection boils and carbuncles, so HS is often misdiagnosed as a skin infection.

When To See a Doctor

In many cases, boils drain spontaneously and go away on their own with a little home care. However, you should talk to your healthcare provider or dermatologist if you have boils and carbuncles that:

• Keep coming back
• Last longer than two weeks
• Cause a lot of pain
• Happen along with a fever

Get medical help right away if a boil or carbuncle is very painful, gets worse quickly, or comes with a fever. A primary care doctor or dermatologist can help determine whether it’s an infection or something else, like HS.

An experienced dermatologist can tell the difference between a skin infection and HS. They can recommend the right treatment — whether that’s draining the bumps or helping you manage HS in the long term.

Join the Conversation

On MyHSTeam, people share their experiences with hidradenitis suppurativa, get advice, and find support from others who understand.

Have you noticed boils or carbuncles on your body? What steps have you taken to help a carbuncle drain? Share with others in the comments below.