Ringworm refers to fungal infections that are on the surface of the skin. Although the world is full of yeasts, moulds and fungi, only a few cause skin problems. These agents are called the dermatophytes. Some common dermatophytic fungi are Trichophyton rubrum, T. tensurans, T. interdigitale, T. mentagrophytes, Microsporum, Canis and Epidermophyton floccosum.