A red bump on the arm that hurts to touch

A tender bump can develop when a hair follicle becomes irritated or inflamed, known as folliculitis. A small spot may also follow an insect bite, minor injury, or blocked pore. If there are many tiny rough bumps on the outer upper arms without much pain, keratosis pilaris is another possibility.

Pain, warmth, pus, rapid growth, and spreading redness make infection more concerning than a stable rough bump. The appearance cannot establish the cause by itself, so note its size, location, onset, and any recent shaving, rubbing, new product, bite, or injury.

Keep the area clean, avoid rubbing or picking, and pause shaving over it. A cool compress may soothe irritation; a warm compress may be more comfortable if it feels like a blocked or inflamed follicle. Do not squeeze or puncture the bump.

Use plain, fragrance-free moisturiser for rough surrounding skin, but avoid applying strong active treatments to broken or draining skin without advice. Photograph the area so you can compare changes rather than repeatedly touching it.

Arrange medical advice if the bump is getting larger, hotter, or more painful, if pus appears, or if redness spreads. Seek urgent help for fever, red streaks up the arm, severe swelling, numbness, reduced movement, or feeling faint or very unwell. Earlier assessment is sensible with diabetes or reduced immunity.

Ask whether the bump looks like folliculitis, keratosis pilaris, or another lesion, and whether it needs a swab or treatment. Ask which changes should prompt urgent review and how to prevent similar bumps.