Acne, which causes pimples on the arms, appears as a result of plugged and inflamed pores, according to Mayo Clinic. Sweat is often a contributor to clogged pores because it traps oil and dead skin cells inside the skin on the body, including on the arms, face, back and legs.
Sweat from bedding and clothing may also contribute to pimples on the arms, according to Men's Fitness Magazine. While sleeping, dead skin cells, oil and sweat rub off onto sheets and clothing, which can absorb into the skin on arms. Cleaning bed linens and changing out of sweaty clothes regularly may reduce the risk of arm acne. Avoiding clothing that is tight and traps sweat that can clog pores may also reduce the risk of arm pimples.
Little bumps that appear to be acne on the arms may also be indicators of a skin condition known as keratosis pilaris, according to WebMD. Plugged hair follicles containing a buildup of protein keratin causes keratosis pilaris. A dermatologist can treat this condition with lasers, topical lotions, ammonium lactate creams or prescription creams. To avoid irritation of acne or skin conditions on the arms, avoid rubbing the skin too hard when showering, and exfoliate the skin gently prior to applying a non oil-based moisturizer.