Erythema means a reddening of the skin. If the condition is just in one area of your body, it can mean that you have inflammation, irritation, or infection of the skin. Erythema over a joint can be a sign of joint infection. When erythema is spread over most of your body, like a rash, it is usually a sign of a more general problem. This could be an allergic reaction, viral or bacterial infection, or an immune system disease.