When a toe nail becomes thick, discolored, and brittle there is a good chance it has been infected with a fungus. This is called onychomycosis or toe nail fungus. If left untreated this can persists for many years, or possibly an entire lifetime. Toes nails often are more supceptable to fungus infections, than fingernail. One reason for this may be, that there is less circulation in the toe area of the body. It could also be caused from the moisture and darkenss of socks. Moisture is a perfect breeding ground for many types of fungi. http://www.Toe-Fungus-Treatment.com