I think I finally understand WTF Nick is talking about when he says "heat allergy" he means Miliaria Rubra. It's a heat rash that is itchy, but it has nothing to do with an allergy, that's an old retarded belief from before modern medicine. For the adults that have it, avoiding hot showers, having your A/C running, and wearing loose clothing made from natural fabrics tends to prevent the problem.
If I had to place a bet it's Nick's choice of clothing that is his main problem. He seems to enjoy wearing synthetic fabrics, which tend to trap moisture against the skin rather than absorbing or wicking it away, which will exacerbate the issue quite a bit. The same goes for anything like a watch/smartwatch that has a band made from synthetic material/metal which will trap moisture against the skin, this is also true for anything like rings. Wearing any type of hat that traps the sweat against the skin can also cause issues.
If I'm right, what a pussy and a retard Nick is. It's not that difficult to prevent recurrence if you follow the rules on how to handle it.