Common (familial) – rough, bumpy skin on upper arms, usually asymptomatic but cosmetically not great. Follicular plugging, basically.
Can get quite inflamed in some people.
Exfoliating, moisturizing may help.
Sometimes goes with inflamed cheeks – Keratosis pilaris rubra faciei, so typical KP of the arms (often perifollicular redness), but can lead to hair loss and atrophy of eyebrows and scalp.
Urea containing (Balneum, Hydromol Intensive, Eucerin intensive) creams or salicylic acid (in zinc oxide) paste may help. Topical steroids can be tried if very red but risky for face, given tendency to atrophy anyway.