Heat rash usually does not require actual medicine, states Mayo Clinic. Rather, cooling the skin and avoiding sweat-inducing activities usually does the trick. For severe cases of heat rash, using 1 percent hydrocortisone cream or calamine lotion helps calm symptoms, according to St. Louis Children's Hospital.
The primary cause of heat rash, also referred to as miliaria, is clogged pores. This occurs when sweat ducts become clogged, trapping sweat underneath the skin instead of escaping as it should, explains Mayo Clinic. Heavy sweating and overheating are common triggers for heat rash, and infants are highly susceptible to miliaria because their sweat ducts are not fully mature.