Hives that become severe when exposed to heat may be caused by vasodilatation or may be related to heat urticaria. Urticaria is caused by irritation due to food, medication, etc., which leads to temporary dilation and increased permeability of small blood vessels in the skin’s mucous membranes. When the environment is hotter, the vasodilation is further exacerbated, so the disease may be aggravated. In addition, it may also be thermal urticaria, also called cholinergic urticaria, which belongs to a type of urticaria. It is a type of urticaria that occurs when the patient is overly emotional, in a hot environment, or exercising a lot. This type of urticaria is temperature-related and can be aggravated by heat. When urticaria is aggravated by heat, you should avoid hot environments and cooperate with your doctor for active treatment.