What causes finger and thumb nail fungus ?

Nail fungus answers: Nail fungus (both finger- and toe-nail) is caused most often by fungal organisms that like skin, also known as dermatophytes. It is less commonly caused by yeasts. It takes a long time to treat it, but it can be successfully and safely resolved with both medicines by mouth and specialized lasers. These 2 may be combined in difficult cases, and topical medicines may also be needed.

Fungus: Pathogens that cause human illness typically fall into three categories: bacterial, viral or fungal. A fungus infection is an illness that results from a fungal pathogen.