For back and arm acne, start with an over-the-counter 5% to 10% benzoyl peroxide wash or a 2% salicylic acid body wash. Leave it on the skin for 2 minutes before rinsing. For stubborn acne, a dermatologist may prescribe topical retinoids or oral antibiotics. Key precautions: 1. Shower immediately after sweating or exercising to prevent clogged pores. 2. Wear loose-fitting, breathable cotton clothing to minimise friction. 3. Avoid scrubbing, picking, or squeezing the bumps to prevent scarring. 4. Use only oil-free (non-comedogenic) moisturisers and sunscreens. Consult a doctor if you see no improvement in 4-6 weeks.