There are many things that can cause a rash including allergic reactions, viral infections and fungal infections, according to WebMD. Parasites, insect bites and serious diseases can also cause a rash.
When a rash occurs, it is a sign that a change is occurring inside or outside of the body. Most commonly, rashes are not serious and they are caused when the skin is exposed to an irritant. When this occurs, the rash typically goes away within a few days. Rashes that do not go away, however, may indicate something more serious. When this occurs, the rash should be checked by a doctor.