Red, sore bump on the arm

A bump around a hair with a pustule can fit Folliculitis, particularly after shaving, sweating, or rubbing. Rough, small bumps on the outer upper arms are often associated with Keratosis Pilaris, although a single tender bump is less typical. A bite, blocked pore, cyst, or localized infection can look similar. Note whether the lump is soft or firm, whether it moves under the skin, and whether redness is expanding.

Keep the area clean, avoid squeezing or puncturing it, and reduce friction from sleeves or straps. A warm, clean compress may ease tenderness when the skin is intact. Avoid shaving across the bump. Photograph it beside a familiar object so changes in size or colour are easier to describe, and arrange an assessment if it persists or recurs.

Get prompt care if the bump enlarges quickly, becomes hot, drains pus, develops red streaks, or is accompanied by fever or feeling unwell. Seek urgent help for severe swelling, facial or breathing symptoms, or rapidly worsening pain. A stable bump that does not settle, repeatedly returns, or remains firm should be examined routinely.

Ask whether the bump is follicle-related, infected, or more consistent with Keratosis Pilaris, and whether it needs a swab or other examination. Mention shaving, new products, bites, injury, drainage, recurrence, and how quickly it changed.