Types of Toenail Fungus: 6 Patterns and 3 Causes Explained

What Are the Main Types of Toenail Fungus?

Toenail fungus, known medically as onychomycosis, is usually described in six main patterns, named for where the fungus enters the nail and how the nail looks. Dermatologists rely on a 2011 classification published in the Journal of the American Academy of Dermatology that recognizes distal and lateral subungual, superficial, endonyx, proximal subungual, and totally dystrophic forms, among others.

If your nails have turned yellow, thick, or brittle, you are far from alone. A 2026 meta analysis found nail fungus in roughly 9% of people in community studies, and a 2020 systematic review in the Journal of the American Academy of Dermatology concluded that it can affect physical comfort, emotions, and appearance. Sorting out the pattern is a helpful first step, and our guide to the early signs of toenail fungus covers what to watch for.

Distal Subungual Onychomycosis (DSO)

DSO is the most common pattern, and it usually begins at the tip of the nail. It is typically caused by dermatophytes, the same group of fungi behind athlete's foot.

• How it starts: The fungus enters at the tip of the nail bed and works its way back toward the cuticle.
• What it looks like: A yellow or brownish color shows up at the edge of the nail. Over time the nail may thicken, turn flaky, and lift away from the nail bed, a change called onycholysis.

White Superficial Onychomycosis (WSO)

WSO affects the top layer of the nail rather than the nail bed underneath, and it makes up about 10% of cases.

• How it starts: Right on the surface of the nail plate.
• What it looks like: Chalky, crumbly white patches appear and can spread across the whole nail, leaving it rough, soft, and prone to crumbling. Because it stays on the surface, it is generally considered more accessible than patterns that sit deeper.

Proximal Subungual Onychomycosis (PSO)

PSO is uncommon in healthy people and is seen more often when the immune system is weakened, for example in people living with HIV. If you notice this pattern, mention it to your doctor.

• How it starts: The fungus begins at the cuticle (the proximal fold) and spreads toward the tip of the nail, the opposite direction from DSO.
• What it looks like: White or yellow spots appear near the cuticle and move outward as the nail grows. The skin around the nail may also look red and swollen.

Endonyx Onychomycosis (EO)

EO is a rarer pattern in which the fungus goes straight into the inner layers of the nail plate.

• How it starts: Instead of creeping in from the tip (like DSO) or the cuticle (like PSO), the fungus invades the inside of the nail directly, bypassing the nail bed and the cuticle.
• What it looks like: A milky white color runs through the full thickness of the nail. The telltale sign is what does not happen: the nail stays firmly attached, and there is no thick, crumbly buildup under it (called subungual hyperkeratosis).

Total Dystrophic Onychomycosis

This is the advanced stage that any of the patterns above can reach when it goes unaddressed for a long time. Rather than a starting point, think of it as where things can end up.

• What it looks like: The entire nail becomes severely thick, opaque, heavily discolored, and crumbly. It may detach completely from the nail bed, which can make walking in tight shoes uncomfortable or painful.

Candidal Onychomycosis

This pattern is caused by a yeast called Candida rather than by dermatophytes. It is less common in toenails than in fingernails, especially for people whose hands spend a lot of time in water.

• How it starts: It usually settles into nails that were already damaged by trauma or an earlier infection.
• What it looks like: The nail turns yellow, brown, or white and often becomes very thick. The skin around the nail is usually involved too, looking red, swollen, and tender (a condition called paronychia).

Mixed and Secondary Forms

Real nails do not always follow the textbook. The same 2011 classification recognizes mixed forms, where more than one pattern shows up on the same nail, and secondary forms, where fungus settles into a nail already changed by an injury or another nail condition. Different toes can also show different patterns at the same time.

How Can You Tell Which Type of Toenail Fungus You Have?

You can narrow it down by noticing where the change starts, what color it is, whether the nail is still attached, and how the skin around it looks. Use the table below as a starting point, not a diagnosis.

Color words are a guide, not a rule. The American Academy of Dermatology lists yellow, white, brown, orange, and even black as possible nail fungus colors, and redness can look different on different skin tones. A 2026 review on nail psoriasis also notes that nail conditions can be harder to recognize in people with skin of color, which is one more reason to get a professional opinion.

Two quick checks can also help you describe things to your doctor: is more than one toe involved, and is the skin between your toes itchy, flaky, or cracked? Athlete's foot often travels with nail fungus.

Which Fungi Cause Toenail Fungus?

Three groups of fungi cause toenail fungus: dermatophytes, yeasts, and nondermatophyte molds. The patterns above describe where the fungus invades, while these groups describe which organism is responsible.

Dermatophytes

Dermatophytes are the leading cause, though estimates of their share vary. A 2020 review put them behind about 90% of toenail cases and named Trichophyton rubrum and Trichophyton mentagrophytes as the main culprits, while a 2026 analysis of 219 studies found them in about 53% of positive samples, with molds and yeasts each near 22%. The mix changes with region, setting, and which nails are tested.

Dermatophytes feed on keratin, the hard protein in skin, hair, and nails, which makes a toenail something like an open buffet. They are also contagious. The American Academy of Dermatology lists touching infected skin or nails, sharing items like towels or nail clippers, and walking barefoot in warm, moist places such as pool decks and locker rooms as common routes. It also notes that athlete's foot can spread into the nails. To go deeper, read our guide on what causes toenail fungus.

Yeasts

Yeasts, mainly Candida albicans, are far more common in fingernails, but they can and do reach toenails, especially nails that are already damaged or lifted. They thrive wherever it stays wet, so sweaty feet in shoes that do not breathe, or frequent water exposure, raise the odds.

Nondermatophyte Molds (NDMs)

Molds such as Fusarium, Acremonium, and Aspergillus live naturally in soil and the environment. They tend to settle into nails already weakened by trauma or earlier damage rather than healthy ones. A 2014 review in the Journal of the European Academy of Dermatology and Venereology proposed that repeated friction from closed shoes may leave toenails more open to these molds.

What Else Can Look Like Toenail Fungus?

Several other nail problems can look just like toenail fungus, including nail psoriasis, damage from pressure or injury, and, rarely, something that needs a closer look, like a dark streak. This is why appearance alone is not enough to know what is going on.

• Nail psoriasis or lichen planus: These skin conditions can thicken, lift, or discolor nails. A 2026 review calls isolated nail psoriasis a frequent mimic of onychomycosis, and a 2025 analysis in Mycoses found fungus more often in people with psoriasis, so the two can show up together.
• Pressure and injury: Tight shoes, sports, or one hard knock can thicken or lift a nail so it resembles fungus. A bruise under the nail usually grows out along with the nail.

Signs That Mean You Should Be Seen Soon

Most nail changes are not urgent, but a few deserve a prompt visit with a doctor:

• A dark brown or black streak in one nail, especially if it widens or the color spreads onto the skin beside the nail.
• A sudden change in just one nail, or pain in a nail.
• Bleeding, an open sore, pus, or spreading redness, warmth, or swelling around the nail.
• Any nail change if you have diabetes or poor circulation.

In a 2026 review of 1,556 people evaluated for dark nail streaks, age 50 and older and involvement of a single nail called for extra suspicion. A 2025 review in Life also linked nail fungus in people with diabetes to a higher risk of secondary infections and foot ulcers, which is why even small changes are worth checking.

Does the Type of Toenail Fungus Change What Happens Next?

Yes, the type can shape how things look and how long a nail takes to grow out, mainly because the depth, the share of the nail involved, and whether the base of the nail is affected all matter. The 2011 classification was designed partly to help doctors estimate outlook, which is why they ask about pattern and not only color.

A simple way to picture it: surface patterns like WSO stay on top of the nail, deeper patterns like DSO and EO involve the nail itself, and total dystrophic involves the whole nail, so it has the most nail to replace.

How Long Does a Toenail Take to Grow Out?

Slowly. In a small study of 22 healthy young adults published in the Journal of the European Academy of Dermatology and Venereology, toenails grew about 1.6 millimeters a month on average, and the big toenail grew faster than the other toes. The AAD notes that a clear big toenail can take a year or longer to grow out, and nail growth tends to slow with age.

Here is a rough timeline for a nail whose underlying problem has been addressed. Your own pace will depend on your age, which toe is involved, and how much of the nail was affected.

1. Months 1 to 3: The visible nail often looks much the same, because the changed part has not grown out yet.
2. Months 4 to 9: A band of clearer nail may appear near the cuticle while the older part moves toward the tip.
3. Months 9 to 18: The changed section keeps moving forward until it can be trimmed away, and a big toenail can take a year or longer.

Why Does Toenail Fungus Keep Coming Back?

Toenail fungus often returns because the same sources of fungus, such as athlete's foot, damp shoes, and shared surfaces, are still around. One expert consensus paper found that the factors behind a first infection, including an earlier infection, older age, an abnormal nail shape, a weakened immune system, and genetic factors, largely drive repeat infections too.

A 2019 review in the American Journal of Clinical Dermatology noted that relapse is likely within about 2.5 years after a nail clears, partly because of ongoing exposure to fungal reservoirs. The same consensus paper stressed properly addressing athlete's foot, checking family members, and good patient education.

Common Risk Factors

The American Academy of Dermatology points to several things that raise the odds:

• Older age, when nails grow more slowly
• Sweaty or damp feet and tight shoes
• Diabetes, poor circulation, or psoriasis
• A history of athlete's foot or earlier nail fungus
• Walking barefoot in shared spaces and sharing nail tools
• A family history of nail fungus

The habits that lower these odds are covered in the next section, and our prevention and hygiene guides go deeper.

When Should You See a Doctor, and What Happens at the Visit?

See a doctor or board certified dermatologist when a toenail changes color, thickens, lifts, or becomes painful and the change does not fade. This guide can help you recognize patterns worth discussing, but it cannot tell you what is happening in your own nail.

The American Academy of Dermatology says nail fungus almost never goes away on its own and can spread, and that testing is sometimes needed to diagnose it. The 2020 review mentioned above also suggests considering laboratory confirmation before starting any regimen.

What Testing Looks Like

1. A look at your nails and feet. Your doctor checks how many nails are involved and whether the skin between your toes is affected.
2. A small sample. This is usually a clipping or scraping from the nail.
3. A lab check. Common options include a microscope exam, a special stain, a fungal culture, or a PCR test.
4. Results and next steps. Ask the clinic when to expect results, since some tests take time.

It helps to bring a few photos of your nail over time, a list of any products you have used, and a note about conditions such as diabetes or psoriasis. Remove nail polish before the visit so the nail is easy to see.

What You Can Do While You Wait

These everyday habits come from the American Academy of Dermatology's prevention tips and help limit spread:

• Keep nails short and clean, and disinfect clippers after each use.
• Dry your feet well, wear dry socks, and change them when they get damp.
• Let shoes dry fully between wears, and rotate pairs when you can.
• Wear sandals or shower shoes in locker rooms, gyms, and pool areas.
• Do not share clippers, towels, or shoes.
• Ask your nail salon how it disinfects tools and foot baths.

Avoid scraping or filing the nail to remove the fungus. According to the AAD, this removes only some of it, because the fungi live in the nail and in the tissue beneath it.

Curious about how fungi compete in nature? Our article on Pythium oligandrum introduces a naturally occurring organism that feeds on other fungi.

Key Takeaways

• Toenail fungus is usually described in six main patterns, based on where the fungus enters the nail and how the nail looks.
• Distal subungual is the most common pattern, white superficial makes up about 10% of cases, and mixed and secondary forms also exist.
• Where the change starts, its color, whether the nail is attached, and the skin around it can help you narrow things down, but a table is a guide and not a diagnosis.
• Dermatophytes are the leading cause, but yeasts and nondermatophyte molds matter too, and their share varies by region.
• Nail psoriasis, injury, and other problems can look like fungus, so a lab test is the reliable way to confirm, and a dark streak, bleeding, pain, or spreading redness deserves a prompt visit.
• Toenails grow slowly, and a clear big toenail can take a year or longer to grow out.
• Fungus often returns when athlete's foot, damp shoes, or shared tools stay in the picture, so dry feet, dry shoes, and personal nail tools help.