Boils: symptoms, causes and treatment

A boil is a painful, pus-filled skin infection that develops around a hair follicle.

It often begins as a tender red or darker-toned bump and becomes firmer or more swollen as pus collects. Several connected boils can form a deeper cluster. Boils may occur anywhere hair grows or friction and sweating affect the skin, including the armpits, groin, buttocks, thighs, face and neck.

Boils commonly present as painful skin lumps. The surrounding skin may feel warm, swollen and sore, while the centre may soften or develop a pale pus point. A boil in an armpit can make arm movement uncomfortable. Fever, rapidly spreading redness, severe pain or feeling generally unwell needs prompt medical assessment.

A boil forms when bacteria enter a hair follicle or a small break in the skin. The immune response brings fluid and infection-fighting cells to the area, creating pus. Shaving irritation, scratching and rubbing can provide an entry point, although a person may not notice any obvious skin injury.

The lump may enlarge and become more tender before it drains or gradually settles. Do not squeeze, pierce or cut it at home because pressure can push infection into surrounding tissue. Recurrent lumps in the armpits or groin, especially when they leave scars or tunnels, deserve a dermatology review because another skin condition may be involved.

Risk can increase with close skin contact, shared towels or razors, crowded living conditions, frequent friction, eczema or other damage to the skin barrier. Diabetes, reduced immune defences and previous boils can also make infection easier to develop or harder to clear.

Diagnosis is usually based on the appearance, location, tenderness and depth of the lump. The clinician may ask about recurrence, drainage, fever, medicines and health conditions. If infection is severe, unusual or keeps returning, a pus sample may help identify the organism and guide antibiotic choice.

A clean warm compress can encourage a small boil to drain naturally. A clinician may make a controlled opening to drain a larger or very painful collection after numbing the area. Antibiotics may be considered when infection spreads into nearby skin, causes systemic symptoms, occurs at a higher-risk site or affects someone vulnerable to complications.

Wash your hands before and after touching the dressing. If the boil drains, clean the surrounding skin gently, cover it with fresh gauze and place used dressings in a sealed bag. Avoid sharing towels, clothing and razors, and wash items that contact drainage before reuse.

Infection can extend into surrounding skin, form a larger abscess or, less often, spread more widely through the body. Seek urgent care for fast-expanding redness, fever with worsening pain, confusion, marked weakness, facial swelling, or a boil near the eye or centre of the face.

Keep cuts clean and covered, use personal razors and towels, shower after heavy sweating and reduce repeated rubbing where possible. Do not share sports equipment without cleaning contact surfaces. Persistent recurrence warrants assessment for skin-barrier problems, bacterial carriage or an underlying health factor.

A primary-care clinician or dermatologist can assess most boils. A clinician experienced in minor procedures may be needed when drainage is appropriate. Arrange prompt care if the lump is rapidly enlarging, on the face, repeatedly returning, or accompanied by fever or spreading redness.