Heat rash which is also known as prickly heat or miliaria  is a medical condition characterised by a painless, but itchy skin rash on the affected area. The skin rash can also be inflamed and presents with little red spots. It mainly appears on parts of the body which collects sweat such as armpits, groin, under the breasts, back, chest, inside of the elbows or knees and the waist.