Does heat rash spread?

Keep cooler: Heat rash usually resolves in a few days unless you continue to sweat too much. So dress in cooler clothes or remove a layer of clothes, blankets, etc. Try not to use any topical creams or ointments that can also hold in heat. Keep cooler and the rash should go away on its own. Cool water will feel good on the rash. Solarcaine gel would help with comfort also.

Yes it can: It can spread if the heat and sweating continues, which causes the heat rash to start with so if you want to prevent the spread use airconditioning or fan and avoid heat and humidity.