Boils and carbuncles

Boils (furuncles), carbuncles, abscesses and pimples are all linked to inflamed skin but differ slightly. For example, a boil is similar to a pimple but has penetrated deeper into the skin and is much more painful. Medical treatment is usually advisable for boils.

At a glance

  • Boils are a purulent form of skin inflammation caused by bacteria.
  • They develop when a hair follicle and the surrounding tissue become inflamed.
  • If several boils merge, a carbuncle is formed.
  • People should never squeeze boils themselves – especially if on the face.
  • If the immune system is weakened, there is a greater risk of boils or other skin infections.
  • About 3 in 100 people who visit their general practitioner due to a skin infection have a boil.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

Boils and carbuncles: doctor wrapping a gauze bandage around an arm.

What is a boil?

Boils are a purulent form of skin inflammation caused by bacteria. They look similar to very large pimples but sit in deeper skin layers and are far more painful.

Boils form when the hair follicles and the surrounding connective tissue become inflamed. Hair follicles consist of a hair, the root of the hair, a sebaceous gland and a small muscle that can make the hair stand on end. The hair follicle inflammation in the case of a boil is sometimes also known as “deep folliculitis” or “perifolliculitis”.

If an infection occurs, the skin tissue in the boil dies creating a pus-filled cavity known as an abscess. Skin abscesses can develop from boils but also result from highly inflamed insect bites or injections with dirty needles. If several boils merge, a carbuncle is formed.

Boils sometimes heal of their own accord without any problems but medical treatment is often useful. This can speed up the healing process, alleviate pain and prevent complications.

What are the symptoms of boils?

Boils are indicated by painful swelling that ranges in size from that of a cherry stone to that of a walnut. The swelling feels warm and is red. Yellowish pus may show through the skin. If several boils merge to form a carbuncle, the inflammation can also trigger a high temperature. This leaves people feeling weak and tired.

Boils primarily form on the face, throat and nape of the neck. However, they can also appear on other parts of the body: in the armpits, groin or genital area, on the back, bottom or thighs.

What causes a boil?

Boils are caused by bacteria, most commonly the pathogen known as staphylococcus aureus. Many people have these bacteria on their skin or in their nasal mucosa, for example, without issue. 

If the immune system is weakened, the risk of boils or other skin infections increases. For example, people with diabetes, a chronic infection or cancer develop boils more often than people who are healthy. Certain allergies such as allergic asthma, eczema or conjunctivitis result in an increased susceptibility to boils.

How common are boils?

Skin infections are very common but most inflammation is caused by something else. About 3 in 100 people who visit their general practitioner due to a skin infection have a boil. 

Doctors diagnose boils in 3 out of every 100 people with a skin infection.

Boils can develop within a few hours or over several days. The pus then escapes from the red, swollen lump after a few days and the boil heals within a few weeks – either by itself or following treatment. A small scar remains.

Boils sometimes heal without the pus coming out. In such cases, the pus is broken down by the body.

How does a boil develop?

If a boil is squeezed or scratched open, the bacteria can spread within the body via the blood or lymph vessels. If a red streak leads away from the boil, for example, the infection is moving along the lymph vessels and the person is said to have lymphangitis. At the same time, the lymph nodes in the affected area can become painfully inflamed. This is known as lymphadenitis.

People who are not familiar with the condition sometimes think the red streaks caused by lymphangitis are a sign of blood poisoning (sepsis). However, this serious and very rare complication only occurs if a huge number of bacteria get into the blood at once and quickly spread throughout the body. 

Important: If boils appear on the face, especially around the nose and upper lip, there is a certain risk of the bacteria getting into the brain, where they could cause meningitis or cerebral venous sinus thrombosis (CVST) – life-threatening blood clots in the large blood vessels.

If people have a weakened immune system, boils can come back repeatedly or appear in several different places at the same time. This is known as furunculosis.

A carbuncle, on the other hand, forms if multiple boils develop in neighboring hair follicles and merge to form a larger suppurative focus. Such carbuncles often form on the back of the neck. They reach deeper into the tissue than a boil.

How can you recognize boils?

Doctors generally recognize boils due to their typical appearance – as well as the symptoms described by the patient. If someone frequently gets boils, has several boils at the same time or is at risk of complications, other investigations such as blood tests or a pus swab may also be required.

The pus is examined in a laboratory. This happens for two reasons: to determine the precise type of bacteria and to make targeted use of antibiotics. Blood tests are also performed. This helps to determine if the inflammation has already spread and whether the patient has any other potential medical conditions that could encourage bacterial infections.

How are boils treated?

The doctor opens the pus-filled abscess with a small cut, disinfects the wound and places strips of gauze inside to soak up and remove the pus. The wound stays open while it heals, i.e. does not need stitching up. People should never squeeze boils themselves – especially if on the face.

If a boil is still growing, the abscess has not yet fully developed. Doctors can check this by feel. In this phase, people can try to start or speed up the healing process by applying warm, moist cloths or a special “drawing ointment”.

Antibiotics are only needed when complications are likely or have already occurred – for example if several boils have developed into a carbuncle. In hospitals, antibiotics are sometimes given as an infusion (via a drip). 

In the case of carbuncles, it is particularly important for them to be cut open to allow the pus to escape. The larger wound is then repeatedly cleaned with antiseptic solutions.

Further information on the topic of boils and carbuncles as well as their treatment can be found at gesundheitsinformation.de.

In cooperation with the Institute for Quality and Efficiency in Health Care (Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen) (IQWiG). As at:

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