Al D’Angelantonio III, D.P.M., Foot & Ankle Surgeon in the Department of Surgery at the Hospital of the University of Pennsylvania
Don't worry. Developing thickened, discolored toenails is a common concern for men and women of all ages. Although there are many reasons that this can happen, it is most often caused by a fungus. Now this sounds a lot worse than it is, but what may be causing your toenails to become thickened and discolored is a “dermatophyte.” It’s a type of microscopic fungus that is invisible to the human eye and loves to hide in dark places like shoes and nesting themselves - you guessed it - right underneath your toenails.
Again, don’t panic. The good news is that these dermatophytes only stay locally to the toenails and do not spread into your blood stream. Other types of dermatophytes can invade the hair and skin. They also won’t cause you to become systemically sick. The bad news is that once the fungus gets underneath your toenails, it is difficult to permanently remove.
If your doctor diagnoses you as having a toenail fungus, you may hear the term “onychomycosis.” Your doctor may test for onychomycosis by sending a clipping of your toenail to a lab where they can look at it under a microscope to detect if the dermatophytes are present. Although being diagnosed with onychomycosis might sound awful, with patience and consistent treatment, your toenails may return back to their normal appearance. However, the longer you wait to treat the toenail fungus, the more likely it is that your toenails may remain permanently discolored.