Small dot-like acne on the back is usually caused by sweat, oil buildup, and friction that block the skin pores. Keep the area clean by washing daily with a mild cleanser, changing clothes after sweating to prevent bacteria and oil from building up, and wearing loose cotton clothing to reduce friction on the skin. Try to shower after exercise and avoid using heavy or oily products on the back, as they can clog pores further. Keep your bedding and towels clean to prevent repeated irritation. If the bumps become painful, spread, or leave marks, they need attention. Consult a doctor for suitable treatment if it does not improve.