Most people experience red bumpy rash in different forms - like lumps, bumps, blisters, and pimples, at least once or twice in their life. Even children and babies are prone to them, in the form of diaper rash. This rash is a type of skin disorder, caused by either contact dermatitis, hives, or allergies. It does not cause major complications, however, some of the rashes combined with conditions like fever may be an indication of serious illnesses. Common places for them to appear are: face, armpits, groin, back, etc.