It is normal when sweating when in hot temperatures. However, it is different from heat allergy sufferers. Besides sweating, they will likely experience other symptoms that cause discomfort, and can even interfere with activities. Although rarely heard, hot allergies can be experienced by anyone. Someone who suffers from a hot allergy will feel itchy and skin rashes arise when in the hot sun, after a hot shower, or when sweating after exercise. Symptoms of a Heat Allergy That Usually Appears Allergy symptoms will usually appear within a few minutes after being exposed to heat. When this is experienced, exposed areas of the body, such as the chest, face, back or arms, will feel itchy and look red or have a rash. Exposure to heat that triggers allergies can be obtained when: Being in the climate or hot weather Sweating while exercising or strenuous activities Hot shower Use tight or thick clothes The rash that appears can be small bumps like mosquito bites or larger. Rashes