I have a reddish bumpy skin rash on the back of both arms..?

Keratosis pilaris: Keratosis pilaris (kp, also follicular keratosis) is a common, autosomal dominant, genetic follicular condition that is manifested by the appearance of rough bumps on the skin. It most often appears on the back and outer sides of the upper arms (though the lower arms can also be affected), and can also occur on the thighs, hands, and tops of legs, flanks, buttocks, or any body part except glabrous.