Hello, Thank you for asking at HCM. I went through your history and would like to make suggestions for you as follows: 1. It is not exactly allergy to heat. I would think of a condition known as cholinergic urticaria . 2. It is a simple benign condition when increase in body temperature, either due to exercise, heat exposure, fever, etc causes red/pink itchy lesions over skin (any part of body), which usually subside by themselves. 3. To control itching, I usually suggest my such patients use of antihistamines such as levocetirizine or cetirizine. 4. Please do not scratch the itchy areas as it would aggravate itching. Hope above suggestions will be helpful to you. Should you have any further query, please feel free to ask at HCM. Wish you the best of the health ahead. Thank you & Regards.