Heat rash is caused when a baby is overdressed or is exposed to hot weather, according to WebMD. Parents who overdress their kids, even when the weather is not very hot, can cause heat rash.
Heat rash looks similar to very small pimples, as described by WebMD, and is usually detected on a baby's head, neck or shoulders. When a baby develops heat rash, it can be aggravated by clothing. A baby who scratches the heat rash also causes irritation. To treat heat rash, parents should start by removing any clothing that is causing the overheating. Air drying instead of towel drying after baths can help alleviate the symptoms of heat rash.