Onychomycosis

Onychomycosis is a fungal infection of the nail that can make your nails thick, discolored, and brittle. While it’s not usually painful, this common condition affects millions of people and can significantly impact daily life and self-confidence.

Table of contents

• What is onychomycosis?
• Other names for this condition
• What causes onychomycosis?
• Who gets onychomycosis?
• Signs and symptoms
• Types of onychomycosis
• Can it spread?
• How is it diagnosed?
• Treatment options
• How to prevent onychomycosis
• What to expect

What is onychomycosis?

Onychomycosis is a fungal infection that affects the fingernails or toenails. This infection can involve any part of the nail, including the nail plate (the hard part you see), the nail bed (the skin underneath the nail), or the nail matrix (the tissue where the nail grows from)^[1]. Toenails are affected much more often than fingernails^[2].

The infection happens when fungi get between your toenail and the nail bed, usually through a crack or cut in your toe^[1]. Once inside, the fungi feed on keratin, a protein that makes your nails hard^[1]. Over time, the nail becomes thickened and discolored as the fungus burrows into the skin under the nail^[10].

tinea unguium, dermatophytic onychomycosis

Other names for this condition

When a specific type of mold called a dermatophyte causes nail fungus, the condition is called tinea unguium. Dermatophytes are responsible for about 90% of toenail fungal infections^[1]. The terms onychomycosis and tinea unguium are often used interchangeably, though onychomycosis is the broader term that includes infections caused by all types of fungi, not just dermatophytes^[3].

What causes onychomycosis?

Onychomycosis is caused by various types of fungi. The most common cause is a dermatophyte called Trichophyton rubrum, which is responsible for about 90% of toenail infections and 50% of fingernail infections^[3]. Dermatophytes are molds that need keratin to grow, which makes your nails an ideal environment for them^[1].

Other organisms can also cause nail infections. Yeasts, particularly Candida albicans, account for about 2% of cases and are more common in fingernail infections^[3]. Non-dermatophyte molds like Fusarium, Aspergillus, and Scopulariopsis brevicaulis are responsible for about 8% of nail infections^[3].

Studies show that about 39% of infections are mixed, meaning they’re caused by more than one type of fungus at the same time, which can make treatment more challenging^[15].

Who gets onychomycosis?

Onychomycosis is very common, affecting approximately 1 in 10 people overall^[1]. The condition becomes much more common with age. About 20% of people older than 60 have nail fungus, and that number increases to 50% for people older than 70^[1][3].

Men are affected more often than women^[7]. In children and adolescents younger than 18 years, the condition is much less common, affecting only about 0.44% of this age group^[15].

Several factors can increase your risk of developing onychomycosis. You may be at higher risk if you have:

• Athlete’s foot (tinea pedis)
• Diabetes
• A disorder that causes excessive sweating (hyperhidrosis)
• A nail injury or trauma
• Poor blood circulation due to peripheral vascular disease
• Psoriasis
• A weakened immune system from conditions like HIV or autoimmune disorders^[1]
• Older age^[15]
• A history of tobacco use^[15]

People with diabetes have a 1.9 to 2.8 times higher risk of developing onychomycosis compared to the general population^[4]. Those with HIV infection have prevalence rates ranging from 15% to 40%^[4].

Signs and symptoms

Toenail fungus typically isn’t painful, but it can be unsightly^[1]. As the infection progresses, you may notice several changes to your nail. Your toenail may change color, looking white, yellow, or brown. It might look chalky or cloudy in some spots^[1].

The nail often becomes thickened and may look misshapen. You might see the nail separate from the nail bed, leaving space between your nail and the skin underneath—a condition called onycholysis^[1][2]. The nail may become brittle, crumbly, or ragged, with pieces breaking off or the nail coming away from the toe completely^[7].

As the disease advances, debris may accumulate under the nail, and the nail may develop a foul smell^[7][15]. If left untreated, the skin underneath and around the nail can become inflamed and painful^[7].

While the physical symptoms may seem minor, many people experience significant emotional and social problems due to the appearance of their nails. This is especially true when fingernails are affected, since hands are always visible^[7]. The condition can also interfere with standing, walking, and exercising^[5].

Types of onychomycosis

Onychomycosis is classified into several types based on how the fungus invades the nail:

Distal subungual onychomycosis is the most common form. In this type, the fungus invades the nail bed and the underside of the nail plate, beginning at the tip of the nail and then moving toward the base. The nail becomes thick and yellow, with debris accumulating under it^[10].

White superficial onychomycosis accounts for about 10% of cases and usually affects toenails. The fungus directly invades the surface layers of the nail plate, forming well-defined white patches that look chalky. As the disease progresses, these patches spread to cover the entire nail, which becomes rough, soft, and crumbly^[10].

Proximal subungual onychomycosis is the least common form in healthy people. The fungus invades through the base of the nail where it meets the skin, penetrates the newly formed nail plate, and moves toward the tip. This form is considered a marker of immune system problems and is more common in people with HIV^[10].

Candidal onychomycosis occurs when yeast invades nails that were previously damaged by infection or injury. This type is more common in fingernails and often affects people who frequently immerse their hands in water^[10].

Total dystrophic onychomycosis represents the most advanced form of any type of nail fungus. In this stage, the entire nail plate is destroyed^[10].

Can it spread?

Yes, many types of nail fungi are contagious. You can spread the fungus to someone else through direct contact, or you can get it by touching an infected surface^[1]. Fungi thrive in warm, moist, dark environments.

Common ways people get toenail fungus include walking around swimming pools, using public locker rooms or showers, and walking barefoot in public areas^[1][8].

Toenail fungus can spread to other parts of your body, though it usually doesn’t spread beyond your toe. When dermatophyte fungi affect your skin, the condition is called ringworm. The infection may spread to other toenails, the skin between your toes (called athlete’s foot), the groin area (called jock itch), or the scalp^[1].

How is it diagnosed?

Your healthcare provider will first examine the affected nail closely to evaluate your symptoms. They may be able to identify nail fungus just by looking at your nail, but laboratory testing is important to confirm the diagnosis^[1][2].

Confirming the diagnosis through testing is essential because only about half of all nail abnormalities are caused by fungus. Other conditions like psoriasis, chronic inflammation, nail trauma, and aging can cause similar changes to nails^[15]. Without proper testing, you might receive treatment that won’t work for your specific condition.

To test for fungus, your healthcare provider will clean the nail with alcohol, then take samples. This might include nail clippings, debris from under the nail, or scrapings from the nail surface^[1][4]. The sample should be collected from the area where fungus is most concentrated, which varies depending on the type of infection.

The most common test is a potassium hydroxide (KOH) preparation, where the sample is placed on a slide with a chemical solution and examined under a microscope^[15]. This test can quickly show if fungi are present.

Other testing methods include fungal culture, which grows the organism to identify the specific type of fungus, and periodic acid-Schiff (PAS) staining, which is a laboratory technique that makes fungi easier to see under a microscope^[4][15]. More recently, polymerase chain reaction (PCR) tests can detect fungal DNA in nail samples^[15].

Treatment options

Not everyone with nail fungus needs treatment, especially if the condition is mild and not bothersome^[2]. However, if your nail fungus causes pain, has led to thickened nails, or affects your quality of life, several treatment options are available. The choice of treatment depends on the severity of infection, how many nails are affected, your overall health, and your preferences.

Oral antifungal medications are the most effective treatment for onychomycosis. These drugs help a new, uninfected nail grow while slowly replacing the infected portion. The most commonly used oral medications are:

Terbinafine is considered the most effective treatment, with cure rates of about 76% according to research studies^[4]. It is typically taken daily for 6 to 12 weeks^[11]. However, you won’t see the final result until the nail grows back completely, which may take four months or longer^[11].

Itraconazole can be taken continuously or in pulse doses (one week per month). Pulse dosing shows cure rates of about 63%, while continuous dosing has cure rates of 59%^[4]. This approach is as safe and effective as continuous therapy but more convenient and economical^[10].

Fluconazole has shown cure rates of about 48%^[4].

Oral medications can cause side effects, including rash and liver damage. Your doctor may order blood tests before starting treatment and again after six weeks to monitor your liver function^[11][20]. These medications may not be recommended for people with liver disease, congestive heart failure, or those taking certain other medications^[11].

Topical antifungal medications are applied directly to the nail. They are less effective than oral treatments but have fewer side effects and drug interactions^[15]. Topical treatments work best for mild to moderate infections that affect less than half of the nail^[15].

Available topical medications include efinaconazole 10%, tavaborole 5%, and ciclopirox 8%. These are applied daily for an extended period, often 48 weeks^[13]. Ciclopirox has a failure rate exceeding 60%^[4], but the newer agents efinaconazole and tavaborole show better results.

Combination therapy using both oral and topical treatments together can increase cure rates^[13].

Nail trimming and debridement—the removal of diseased nail tissue—when used along with medication can improve treatment results^[15]. Filing down the surface of the nail may help topical medications penetrate better^[20].

Laser therapy is a newer treatment option that uses targeted light to destroy fungal cells without damaging surrounding tissue^[14][18]. This may be helpful for chronic infections that haven’t responded to traditional treatments, though more research is needed.

In severe cases, surgical removal of the nail may be considered^[13].

How to prevent onychomycosis

You can take several steps to reduce your risk of developing or spreading nail fungus:

Keep your feet clean and dry. Wash your feet daily with soap and water, paying special attention to the spaces between your toes. Dry your feet thoroughly afterward, including between the toes^[17][24].

Choose appropriate footwear. Select shoes made from breathable materials that allow air circulation. Avoid tight-fitting shoes that trap moisture^[1]. Consider using antifungal sprays or powders in your shoes^[18].

Wear socks that wick away perspiration. Change socks regularly, and choose fabrics that help keep feet dry^[20].

Keep nails trimmed and clean. Trim nails short and file down any thickened areas^[17][24]. Use separate nail clippers for infected nails to avoid spreading the infection^[17].

Protect your feet in public areas. Wear flip-flops or shower shoes in communal areas like pools, locker rooms, and public showers^[8][15].

Disinfect shoes and socks to reduce the risk of reinfection^[15]. Not using old shoes after successful treatment may help prevent the fungus from coming back^[1].

Maintain a strong immune system through a balanced diet, regular exercise, and adequate sleep, as this can help your body fight off infections^[18].

What to expect

Even with treatment, nail fungus often comes back. The recurrence rate ranges from 10% to 50% due to reinfection or incomplete clearing of the original infection^[4][15]. Some sources report a 25% relapse rate^[15].

Treatment success rates are generally lower in adults over age 65^[11]. Because nails grow slowly—toenails take 12 to 18 months to completely regrow—seeing results from treatment takes time^[12].

Onychomycosis should be considered a condition to be managed rather than permanently cured in many cases^[10]. Once a nail has separated from the nail bed, it won’t reattach, though the nail will continue to grow from the base^[20].

While not life-threatening, untreated onychomycosis can lead to complications. These may include pain, difficulty walking, lower leg cellulitis (a bacterial skin infection), and in severe cases, more serious problems like tissue damage or nail loss^[3][5]. The condition can be particularly problematic for people with diabetes or weakened immune systems^[15].

Preventive measures and ongoing care can help reduce the likelihood of the infection returning after successful treatment.