Ringworm is a common fungal infection that can cause a red or silvery ring-like rash on the skin. Ringworm commonly affects arms and legs, but it can appear almost anywhere on the body.Despite its name, ringworm doesn't have anything to do with worms.ingworm is a common fungal infection that can cause a red or silvery ring-like rash on the skin. Ringworm commonly affects arms and legs, but it can appear almost anywhere on the body.