When exercising with humid weather my upper leg got red warm and a bit itchy but the lower leg didnt.allergy?why that happens?

Lower leg exposed?: You may have what is called cholinergic urticaria in the early stage because there have been no hives. This happens during the cooling period after a rise in core body temperature.If your lower legs are not covered by clothing, the temperature may be cooler and thus no itching. Try an antihistamine 2 hours before exercise when the weather is humid.