Why does an aerosol spray can feel colder after use?

Aerosol cans (like hairspray, whipped cream, or spray paint) work by using a propellant—usually a liquid under high pressure—that pushes the product out when you press the nozzle. Inside the can, the propellant is kept as a liquid because the pressure is high. When you spray, the pressure at the opening suddenly drops, causing some of the propellant to rapidly evaporate (turn from liquid to gas) in order to escape the can. This phase change from liquid to gas requires energy, known as the heat or 'latent heat of vaporization.'

Where does this energy come from? The propellant takes that heat from the surroundings—including the remaining liquid in the can and the metal walls of the can itself. As a result, the can gets colder. This is very similar to how sweat cools you off: When sweat evaporates, it absorbs heat from your skin. Some aerosol cans, if sprayed continuously, can even get cold enough to form frost on the outside! This cooling effect is a normal result of the physics of rapid evaporation under pressure.