There's a guy who works out in the gym and I was talking to him and he said that when he works out, the creases on the inside of him arms sweat and get this rash. What causes that does anyone know?
Some people get hives from exercise, it's called a physical allergy or physical hives. (You can be "allergic" to cold, heat, sweat, sunlight, water, even strong emotions)
For most folks the symptoms remain mild, OTC antihistamines can help.