Small hard lump under skin on arm: what should you know?

A bump near a hair follicle may be red, sore, or related to shaving, rubbing, or a minor skin injury. A boil tends to become more tender and warm as inflammation develops. A lump that is smooth and moves beneath the skin can behave differently from one that is fixed to the skin or deeper tissue. A persistent scaly, crusted, shiny, or bleeding surface should be examined; basal cell carcinoma is one possible skin diagnosis, but a lump's appearance cannot confirm it.

Record whether it is on the upper or lower arm, whether the size or colour changes, and whether nearby skin feels hot.

Do not pick, squeeze, or puncture the area. Keep it clean, reduce rubbing from tight sleeves or straps, and use a warm compress for comfort if it is tender. Take a dated photograph and note any recent bite, cut, injection, or new product. Arrange a clinical review if it lasts, recurs, becomes larger, or is difficult to distinguish from surrounding tissue. Treatment depends on the diagnosis and may involve observation or a targeted procedure.

Seek prompt care when pain, warmth, swelling, or redness is increasing, especially if pus or fever appears. Have a clinician assess a hard fixed lump, a wound that does not heal, repeated bleeding, or a rapidly changing surface. Get urgent help for severe swelling, red streaking up the arm, or feeling very unwell.

Ask whether the lump is in the skin, fat, or deeper tissue, whether an infection is present, and what change should trigger re-examination. Ask whether a biopsy, drainage, or another test is needed, and which treatments could reduce inflammation safely.