The development of nail fungus results from the interaction of environmental and genetic factors. Environmental factors consist of conditions that allow for fungus to grow. Examples include humid environments and tight-fitting shoes.[1] Genetically, certain mutations related to impaired immune function may increase the risk of developing nail fungus.[2] This may explain why some people do not develop nail fungus while being exposed to the same environmental factors.
Other things such as older age, psoriasis, nail trauma, peripheral vascular disease, smoking, and immune suppression also increase the risk of developing nail fungus.[1]