Heat Rash is also known as Prickly Heat. Heat Rash can happen to anyone be it a baby or a full grown adult. Heat Rash usually occurs when the weather is hot and humid. It develops due to the sweat duct getting blocked, resulting in blisters and red, inflamed skin, It can also cause a 'prickling' or stinging sensation. It is also referred to as Miliaria crystallina. Heat rash can be superficial in which case the blisters formed are small and clear. They are not as painful and will clear up without medication unless the hot humid weather returns.
The Heat rash which affects the deeper layer of the epidermis is called Miliaria rubra. Also known as "prickly heat". Develops in adults who are in bed rest during the hot ans humid summer months. Infants mostly develop this during the first and third week. It is characterized by itch prickly bumps.
The third kind is the Miliaria profunda which occurs in the dermal layer of the skin below the epidermis and so is a deeper rash. It occurs in people who exercise an sweat a lot. Red lesions.