Keratosis pilaris is a harmless, very common skin condition causing small rough bumps, typically on the upper arms, thighs and cheeks. It occurs when keratin plugs hair follicles, and it often runs in families alongside dry skin or eczema.
It needs no treatment, but appearance can be improved with regular moisturisers containing urea, lactic acid or salicylic acid, and it often settles with age. Scrubbing aggravates it. A doctor can confirm the diagnosis if there is doubt, since it is sometimes mistaken for acne.