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Toenail Fungus (Onychomycosis)

Medically reviewed by Last updated on Feb 19, 2024.

What is Toenail Fungus (Onychomycosis)?

Harvard Health Publishing

Toenail fungus is a condition that disfigures and sometimes destroys the nail. It is also called onychomycosis  

Toenail fungus can be caused by several different types of fungi. Fungi are microscopic organisms related to mold and mildew.  

These fungi thrive in the dark, moist and stuffy environment inside shoes. As they grow, fungi feed on keratin. Keratin is the protein that makes up the hard surface of the toenails.  

Factors that increase the risk of developing toenail fungus include: 

However, many people with toenail fungus have no clear risk factors. 

Toenails 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 friction from the sides of shoes. 


When a toenail develops a fungal infection, it typically turns yellow or brown. It becomes thick and overgrown. Foul-smelling debris also may accumulate under the nail.  

As the infection continues, the nail may crumble gradually and fall off.  Or, it may become so thick that the affected toe feels uncomfortable or painful inside shoes. 

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


You will describe your foot symptoms to your doctor. He or she will ask about any factors that may increase your risk of toenail fungus. These include: 

A skin disease called psoriasis sometimes can cause nail problems that look similar to a fungal infection. As a result, your doctor may ask whether you or a family member has psoriasis. It is possible for psoriasis and a fungal infection to affect the same toenail.  

Your doctor will examine your affected toenail or toenails. Often the diagnosis can be made based on the appearance of toenails. Your doctor may take small samples of the affected nails. These samples will be sent to a laboratory where they are tested for fungi and other infectious agents. 

Expected Duration

Toenail fungus rarely heals on its own. It is usually a chronic (long-lasting) condition. It can gradually worsen to involve more and more of the nail. Even if the affected nail comes off, the new nail may be infected with fungus. 


To help to prevent toenail fungus:  


Treatment may begin with your doctor removing as much of the infected nail as possible. This can be done by trimming the nail with clippers or filing it down. 

If the infection is mild and limited to a small area of your nail, your doctor can prescribe a topical antifungal agent in the form of a cream, solution or medicated nail polish.  

If the infection is in a wider area of your nail, or several nails, a topical agent alone is less likely to be effective. So, your doctor may prescribe an oral antifungal medication. Most commonly doctors prescribe terbinafine (Lamisil) first. A commonly used alternative is itraconazole (Sporanox), but it can cause serious drug interactions.  

In very severe cases, when toenail fungus is resistant to treatment, it may be necessary to remove the entire nail surgically. 

Treatment options

The following list of medications are in some way related to or used in the treatment of this condition.

View more treatment options

When To Call a Professional

You don't need to call your doctor unless you have pain or difficulty walking. You can show your doctor your toenails at your next office visit or schedule an appointment if you want to discuss treatment with a prescription medication. 


Most people treated with an oral antifungal medicine are cured after a few months of therapy. However, even after the fungus is dead, the nail may never become clear and normal-looking. 

The fungus returns in some people even after successful treatment with an oral antifungal medication. 

Additional Info

National Institute of Arthritis and Musculoskeletal and Skin Diseases

American Podiatric Medical Association (APMA)

American Academy of Dermatology

Learn more about Toenail Fungus

Treatment options guides (external)

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.