Why do I get bumps on the back of my arms?

Small rough bumps on the backs of the upper arms - sometimes the thighs, cheeks, or buttocks too - are almost always keratosis pilaris: keratin, the protein in skin, plugs the hair follicles instead of shedding, leaving a sandpapery, goosebump texture sometimes called chicken skin. The AAD notes it is harmless, extremely common - affecting a large share of teens and many adults - runs in families, comes with dry skin and eczema, and flares in winter when skin dries out. It is not acne, not contagious, and not a hygiene problem. It often fades substantially by adulthood. Smoothing it: the goal is managing texture, not curing - gentle chemical exfoliants beat scrubbing, which inflames the bumps: lotions with lactic acid, urea, or salicylic acid, used daily for weeks; short lukewarm showers; thick moisturizer straight after, since dryness feeds the plugs; and no picking - picked KP leaves dark marks and scars. Retinoid creams from a dermatologist are the next step when over-the-counter is not enough. When bumps are something else: bumps that itch intensely, weep, or spread fast; bumps arriving suddenly as an adult all over rather than the classic arm-thigh distribution; or bumps with other symptoms. Classic KP needs no medical visit at all - it is a cosmetic texture question, and the routine above is the entire playbook. Pymander is a free AI doctor, 24/7 by text. Describe the bumps and how long they have been there, and it can confirm the pattern.