Approximately 32 million people in the United States develop toenail fungus … and something other than not wearing shoes on the pool deck or in the gym shower may be to blame.

People may have their parents to thank when they develop the brown, wrinkly toenails caused by an infection from the same fungus that causes athlete’s foot. A 2002 study suggested that your susceptibility to get the infection is a single-gene, dominant trait.

The same study showed that even in a married couple in which one person has the infection and the other doesn’t, the infection-free person rarely develops the infection. But half of the couple’s children did develop the disease, suggesting your genes determine your susceptibility. And because the infection is not life-threatening, there is likely little interest in dedicating research funding to finding the gene that determines a person’s susceptibility.

A group of fungi called dermatophytes (dər-ˈma-tə-ˌfīt) causes the infections. Once established, these fungi can be difficult to oust. The disease infects not only the nail, but the nail bed as well, sending filaments of fungus down into your flesh. Because of this, topical treatments may work best for less-established infections.

Deeper infections may only yield to oral medications, which can attack the infection from the bloodstream. The most effective oral medication is Lamisil, according to dermatologists.

But don’t expect clear nails overnight. The infected part of your nails could take months, or even a year, to grow out. And once you’re rid of the infection, take care in the areas where you likely caught the affliction in the first place: pool decks, locker room floors and even carpets can harbor the fungus. Be sure to wear shoes in these areas and to disinfect your home regularly.