Onychomycosis (Toenail Fungus)

What Is It?

Toenail fungus, also called onychomycosis, is a relatively common condition that disfigures and sometimes destroys the nail. Onychomycosis can be caused by several different types of fungi (microscopic organisms related to mold and mildew). These fungi thrive in the dark, moist and stuffy environment inside shoes. As they grow, they feed on keratin, the tough protein that makes up the hard surface of the toenails. In most cases, the fungus belongs to a group of fungi called dermatophytes, which include Trichophyton rubrum and Trichophyton interdigitale. Other, less common causes of onychomycosis include yeasts and molds.

Toenail fungus affects 2 percent to 18 percent of all people worldwide and 3 percent to 5 percent of people in the United States. It is relatively rare in children, affecting only about one out of every 200 people younger than 18. However, the likelihood of getting toenail fungus increases with age, so that up to 48 percent of people have at least one affected toe by the time they reach age 70. Although 2.5 million Americans see a podiatrist annually for treatment of toenail fungus, many more are infected but never seek help. Some people consider toenail fungus just a cosmetic problem, and don't bother seeking treatment.

Almost anyone who wears tight-fitting shoes or tight hosiery has an increased risk of developing toenail fungus, especially if they also practice poor foot hygiene. Wearing layers of toenail polish, which doesn't allow the nail to breathe, is another risk factor. Also, because toenail fungi may spread from foot to foot on the floors of showers and locker rooms, fungal infections of the toenails are especially common among military personnel, athletes and miners. The condition also tends to affect people with chronic illnesses, such as diabetes or HIV, as well as people with circulatory problems that decrease blood flow to the toes. However, many people have no clear risk factors.

Of all the toenails, those on the big toe and little toe are the most likely to develop a toenail fungus. This may be partly because the big toe and little toe are constantly exposed to the mild trauma of friction from the sides of shoes.

Symptoms

When a toenail develops a fungal infection, it typically turns yellow or brown and becomes thick and overgrown. Foul-smelling debris also may accumulate under the nail, especially at the sides and tip. As the infection continues, the nail either may crumble gradually and fall off or become so thick that the affected toe feels uncomfortable or painful inside shoes.

In a less common variety of toenail fungus, called white superficial onychomycosis, the nail turns white rather than yellow or brown, and the surface becomes soft, dry and powdery.

Diagnosis