Tinea unguium is a fungal nail infection caused specifically by a group of fungi called dermatophytes. It falls under the broader umbrella of onychomycosis, which covers all fungal nail infections regardless of the type of fungus involved. When your doctor says “tinea unguium,” they’re identifying the most common form of fungal nail infection, affecting an estimated 4% of people worldwide and showing up far more often in toenails than fingernails.
How It Differs From Other Nail Fungus
Onychomycosis is the general term for any fungal infection of the nail. It can be caused by dermatophytes, yeasts, or environmental molds. Tinea unguium refers only to infections caused by dermatophytes, a family of fungi that feed on keratin, the protein that makes up your nails, skin, and hair. Since dermatophytes are responsible for the vast majority of fungal nail infections, tinea unguium and onychomycosis are often used interchangeably in practice, even though they’re technically not the same thing.
The dominant culprit is a fungus called Trichophyton rubrum, which accounts for roughly 40% of cases. The second most common is Trichophyton mentagrophytes, responsible for about 26% of infections. These two species cause the overwhelming majority of tinea unguium cases across Europe, North America, and Asia.
What It Looks Like
Tinea unguium typically starts at the free edge of the nail (the tip you trim) and works its way back toward the base. You’ll notice yellow or white streaks along the nail, either spreading across the full width or appearing in thin lines. As the infection progresses, the nail thickens, becomes brittle, and may start to crumble or crack at the edges. The nail can also lift away from the skin underneath, creating a gap where debris collects.
In less common cases, the infection begins as white, chalky patches on the surface of the nail rather than underneath it. This form is called white superficial onychomycosis and tends to be easier to treat because the fungus hasn’t penetrated deeply. A rarer pattern starts at the base of the nail near the cuticle and grows outward, which is more often seen in people with weakened immune systems.
Most people first notice a single toenail is affected, usually the big toe. Left untreated, the infection can spread to adjacent nails over months or years.
Tinea Unguium vs. Nail Psoriasis
Several nail conditions mimic the appearance of tinea unguium, but nail psoriasis is the most commonly confused. A few visual clues help distinguish them. Psoriasis tends to produce small pits or divots on the nail surface, as if someone pressed a tack into the nail. It also causes reddish-brown splotches called “oil spots” underneath the nail, something fungal infections don’t produce. When psoriasis lifts the nail from the bed, there’s often a distinct reddish line along the border of the detached area.
Fungal infections, by contrast, produce streaky discoloration and significant thickening. They also favor toenails almost exclusively, while psoriasis more commonly affects fingernails. A single affected toenail points toward fungus or trauma rather than psoriasis. Because the conditions can look similar, lab testing is important before starting treatment.
How It’s Diagnosed
A visual exam alone isn’t reliable enough to confirm tinea unguium. Up to half of abnormal-looking nails turn out not to be fungal at all, which is why lab confirmation matters. The most common first step is a KOH preparation: a sample of nail debris is dissolved in a potassium hydroxide solution and examined under a microscope to look for fungal structures. This confirms whether a fungus is present but can’t identify which one.
A fungal culture takes the diagnosis further by growing the organism in a lab to identify the exact species. This process can take several weeks. When both the KOH test and culture come back negative but the nail still looks suspicious, a nail biopsy stained with a special dye (PAS stain) can catch infections the other tests miss. PAS staining is the most sensitive diagnostic method, detecting fungus in nearly 99% of confirmed cases.
Who’s Most at Risk
Age is the strongest risk factor. Tinea unguium becomes increasingly common as you get older, partly because nails grow more slowly with age, giving fungi more time to establish themselves, and partly because circulation to the feet decreases. Men develop toenail infections more frequently than women, possibly due to greater use of closed-toe shoes and higher rates of nail trauma from physical activity.
Diabetes significantly raises the risk. Chronic high blood sugar impairs the immune cells responsible for fighting off fungal invaders, and poor circulation to the feet creates an environment where infections thrive. Research shows a clear link between higher blood sugar levels (measured by HbA1c) and increased rates of fungal infection in the feet. People with diabetic foot ulcers or peripheral vascular disease are especially vulnerable, with fungal infections at the toenail, between the toes, and on the sole all occurring at higher rates.
Other factors that increase susceptibility include immunosuppression from medications or illness, a history of athlete’s foot (which is caused by the same family of fungi and can spread to the nails), repeated nail trauma, and infrequent foot washing. Working in warm, damp environments or sharing communal showers also raises your exposure.
Treatment Options
Oral Antifungal Medications
For moderate to severe infections, oral antifungal pills are the most effective option. Terbinafine, taken daily for about 12 to 16 weeks, consistently produces the highest cure rates, ranging from roughly 65% to 90% depending on how severely the nail is affected. It works by accumulating in the nail and killing dermatophytes directly.
Itraconazole is the main alternative. It can be taken daily or in a “pulse” pattern (one week on, three weeks off, repeated for several cycles). Cure rates with itraconazole are somewhat lower, typically falling between 50% and 82%. One large comparative study found terbinafine achieved clinical and mycological cure rates of 73% and 76%, while itraconazole reached 48% and 50% over the same treatment period. Your doctor may choose one over the other based on other medications you take, since both can interact with certain drugs.
Because toenails grow slowly (roughly 1 to 1.5 millimeters per month), you won’t see a fully clear nail until months after treatment ends. It can take 12 to 18 months for a big toenail to completely grow out and replace the damaged portion.
Topical Treatments
For mild infections that haven’t reached the base of the nail, topical antifungals applied directly to the nail surface are an option. Three products are commonly used: efinaconazole 10% solution, tavaborole 5% solution, and ciclopirox 8% nail lacquer. These are applied daily for 48 weeks.
Topical treatments are safer than oral medications since they don’t pass through your liver, but they’re considerably less effective. In clinical trials, complete cure rates (meaning both clear nail and no detectable fungus) were 15 to 18% for efinaconazole, 7 to 9% for tavaborole, and 6 to 9% for ciclopirox. Mycological cure rates, meaning the fungus was eliminated even if the nail hadn’t fully cleared, were higher: around 53 to 55% for efinaconazole and 31 to 36% for the other two. These numbers reflect the challenge of getting medication through the hard nail plate to reach the fungus underneath.
Recurrence and Prevention
Even after successful oral treatment, tinea unguium comes back in 20 to 25% of cases. The fungus can persist in surrounding skin (especially if athlete’s foot is present), in shoes, or in the environment. Reinfection from these sources is the primary driver of recurrence.
Reducing your risk of a first infection or a recurrence involves keeping feet dry, changing socks daily, wearing breathable footwear, and using sandals in communal wet areas like gym showers and pool decks. Treating any concurrent athlete’s foot is essential, since the same dermatophytes cause both conditions and the skin infection serves as a reservoir. If you have diabetes, maintaining good blood sugar control and washing your feet regularly both lower the likelihood of fungal nail infections taking hold.