Fungal infection is characterized by a yellowish discoloration in the nail plate, nail plate separation from the nail bed and apparent debris in the area of separation. Please see your physician for a proper diagnosis and prescription. Fungus can spread from one nail to another if you use the same files and implements on the infected nail as you do the others. Always sanitize your files and implements after use. You can do this by washing them with warm soapy water, rinse them and then totally immerse them in a mixture of 1 part clorox to 10 parts water for a full 10 minutes, then wash them again. Dry them really well and then store them in a sealed container until the next use. Fungal spores can live in the nail file because there is debris in the file from using it.