I have, however, had patients who suggested they had gotten other types of infections in a salon. But fungi can't infect healthy nails that have a good vascular supply because fungi also need a warm, moist environment to survive. Some type of trauma usually precedes fungal infections of the nails, whether a person stubs her toe or wears poor-fitting shoes. It often takes four to five months for onychomycosis to become apparent, though, and many people have forgotten the original injury by then. People are not only living longer, they're exercising more.
Exercise can traumatize the nail and break the seal between the nail plate and nail bed.
Other risk factors include poor circulation such as caused by peripheral vascular disease. Also, trauma creates a portal for the fungi to invade the undersurface of the nail. The toenails are exposed to much more trauma and abuse than the fingernails. The feet also are more susceptible to fungal infections of the skin because they spend so much time encased in socks and shoes, which foster the dark, moist environment fungi thrive in. As for the infected nail, you can safely file it down, carefully clip it back, and apply polish.