Heat rash occurs when pores become clogged and can’t expel sweat. This is more likely to happen in warmer months, in warmer climates, and after intense exercise. Wearing certain clothing can trap sweat, leading to heat rash. Using thick lotions and creams can also lead to heat rash.
It’s possible to get heat rash in cooler temperatures if you wear clothes or sleep under covers that lead to overheating. Babies are more likely to develop heat rash because their pores are underdeveloped.