Itching on your back after eating foods like chilli or spinach is most likely due to a food-triggered allergy or sensitivity, sometimes related to Urticaria, where certain foods release histamine in the body and cause itching. Since anti-allergic medicines give only temporary relief, the best long-term approach is to identify and avoid your specific triggers, keep a food diary, and reduce intake of spicy or high-histamine foods. Wearing loose cotton clothes, keeping the skin cool, and using a good moisturiser can also help reduce irritation. For persistent symptoms, a doctor may advise regular (non-drowsy) antihistamines for a longer period or further evaluation to confirm the cause. If the itching becomes severe, spreads, or is associated with swelling or breathing difficulty, seek medical care promptly.