As the rash worsens, the bumps or blisters may expand, become irritating or itchy, and redden. Although prickly heat can be transmitted on the body, it is not contagious. There is no method to spread the rash to other persons under normal circumstances. However, if you scratch the area where the rash is found, you may transfer virus into the skin wound which could then be touched by someone else. Prickly heat is caused by a lack of moisture in the skin. When there is a shortage of water in the body, the sweat glands don't have anything to release so they just fill up with saltwater. This causes the skin to feel tight and prickly. The more dehydrated you are, the worse prickly heat will be. Eating plenty of salty foods may also cause your body to retain water, which could lead to prickly heat. In very hot conditions, your skin needs more water than usual. So when sweating doesn't come out fast enough, the only way for your body to get rid of the excess heat is by drying out its own tissues. This process leads to irritation and inflammation of the skin, which is why people often say that heat makes the body "burn" itself from the inside out. Prickly heat is usually gone once you have a chance to drink some water.