A sun rash is seen as small, reddish blisters or small or large spots in areas that have been exposed to sunlight.The only remedy is to use a sunscreen with a high sun protection factor. On the other hand, heat rash develops when your sweat ducts become blocked and perspiration is trapped under your skin. In particular, miliaria rubra causes red bumps that are intensely itchy or prickly, giving rise to its common name, prickly heat. There is often little or no sweating in the affected areas adults develop miliaria rubra shortly after they're exposed to hot weather, but the rash more often appears after several months of exposure. The best treatment for any form of heat rash is to reduce sweating and wearing lightweight clothing. Once the skin is cool, heat rash tends to clear quickly. Take care and keep us posted.