Itching with black and red pimples on the back can occur due to many reasons including acne, clogged pores, sweat and friction, heat rash, allergic or irritant reactions, or fungal infections, and because the exact cause can vary based on skin type and individual factors it is essential to consult a doctor for proper diagnosis and a personalised treatment plan that may include suitable medications, gentle skin care products, lifestyle measures like avoiding tight clothing and managing sweat, and guidance on diet if needed, meanwhile keeping the area clean and dry, using a mild non comedogenic body wash, avoiding scratching, and changing clothes after sweating may help reduce symptoms.