Hard lump on forearm under the skin

The forearm contains skin, fatty tissue, muscle, tendons, nerves, and bone, so a bump may come from different layers. A benign fatty or fibrous growth can feel rubbery or firm and sit beneath normal-looking skin. A blocked or inflamed structure may be sore, warm, or red. A boil is usually an inflamed, tender lump that can collect pus. A persistent surface lesion should be checked because basal cell carcinoma can present as a non-healing or bleeding skin change.

A clinician will ask about injury, injections, insect bites, medicines, and how the lump has evolved. They may compare both arms and check sensation, circulation, and nearby joints before deciding whether further testing is needed.

Measure or photograph the area only occasionally so you can describe change without irritating it. Do not cut into it, drain it, or apply strong products. Book a routine clinical review if it remains present, becomes bothersome, or is difficult to classify by touch. Bring a list of medicines and mention any recent trauma or skin infection. Treatment depends on the finding and may range from monitoring to a procedure.

Get prompt advice for rapid enlargement, increasing pain, warmth, redness, pus, fever, or a red streak spreading along the arm. Seek urgent care for new weakness, numbness, marked swelling, or a lump following significant injury. A lump that is fixed, repeatedly bleeding, ulcerated, or changing in colour should be assessed without delay.

Ask which tissue layer seems involved, whether the lump needs imaging, and what diagnosis the examination supports. Ask how soon it should be rechecked, what growth or skin changes matter, and whether removal would provide useful information or relief.