Onychomycosis

What is onychomycosis?

Onychomycosis is the medical term for a fungal infection of the nail. It happens when microscopic fungi grow in or under a fingernail or toenail, slowly damaging the nail plate — the hard, visible part of the nail. Over time the infected nail often becomes discolored, thickened, brittle, or misshapen. Many people know the condition by its everyday names: fungal nail infection or, when it affects the toenails, “toenail fungus.”

So what is onychomycosis in practical terms? It is one of the most common nail disorders seen by doctors, and it accounts for a large share of all nail problems in adults. Toenails are affected far more often than fingernails, mainly because feet spend long hours in warm, moist shoes and socks — an environment in which fungi thrive. The condition can occur at any age, but it becomes more common as people get older. Older adults, people with diabetes, people with reduced blood flow to the feet, athletes, and people whose immune systems are weakened are all more likely to develop it.

Onychomycosis is rarely dangerous on its own, but it usually does not go away by itself. Without treatment it tends to progress slowly, can spread to other nails or to the surrounding skin, and in vulnerable people — particularly those with diabetes — it can open the door to more serious skin and soft-tissue infections. In hospital settings, the condition is typically managed by a dermatology department, which specializes in diseases of the skin, hair, and nails.

Symptoms of onychomycosis

Onychomycosis symptoms usually develop gradually, often over months or years. In the early stages many people notice only a small cosmetic change and feel no pain at all. As the infection advances, the nail changes become more obvious and can start to cause discomfort.

Common signs and symptoms include:

• Discoloration: the nail may turn white, yellow, brown, or occasionally greenish or black, often starting at the tip or edge of the nail.
• Thickening: the nail plate becomes thicker than normal and may be hard to trim.
• Brittleness and crumbling: the nail may become fragile, ragged, or crumbly at the edges.
• Change in shape: the nail may become distorted, lifted, or curved.
• Debris under the nail: a chalky or powdery buildup, made of nail fragments and fungal material, can collect beneath the nail plate.
• Separation of the nail: the nail may partially detach from the nail bed underneath, a change doctors call onycholysis.
• Odor: some infected nails give off a mild, unpleasant smell.
• Discomfort or pain: in later stages, thickened or distorted nails can hurt when walking or wearing shoes.

Doctors also describe several patterns, or types, of onychomycosis, and the symptoms differ slightly between them. In the most common type, called distal subungual onychomycosis, the infection starts at the far end of the nail and under its free edge, then spreads back toward the base; discoloration and debris under the nail tip are typical first signs. In white superficial onychomycosis, the fungus grows on the surface of the nail plate, producing chalky white patches that can sometimes be scraped off. In the less common proximal type, changes begin near the cuticle at the base of the nail — this pattern is seen more often in people with weakened immune systems. In advanced or “total dystrophic” disease, the entire nail is thickened, crumbly, and destroyed.

Because many other conditions — including psoriasis (a chronic skin disease), nail injury, and normal age-related changes — can make nails look similar, nail changes alone do not confirm a fungal infection. That is why proper testing matters before starting long courses of treatment.

Causes and risk factors

The main onychomycosis causes are fungal organisms. Most infections are caused by a group of fungi called dermatophytes — the same organisms responsible for athlete’s foot, a fungal infection of the skin between the toes and on the soles. Less often, yeasts (such as Candida) or non-dermatophyte molds are responsible, particularly in fingernails or in nails that were previously damaged.

Fungi enter the nail through small cracks in the nail or the surrounding skin, or through the gap between the nail and the nail bed. Once inside, they feed on keratin, the protein that gives nails their hardness. Warm, dark, and moist conditions — such as the inside of closed shoes — help them multiply.

Several factors increase the risk of developing onychomycosis:

• Older age: nails grow more slowly and blood circulation decreases with age, making infection more likely and harder to clear.
• Athlete’s foot: untreated fungal infection of the skin of the feet often spreads to the nails.
• Excessive sweating of the feet, or wearing tight, non-breathable shoes for long periods.
• Walking barefoot in communal wet areas such as swimming pools, gym showers, and locker rooms.
• Nail injury: trauma from sports, ill-fitting footwear, or aggressive manicures and pedicures can damage the nail’s natural barrier.
• Diabetes: reduced circulation, nerve changes, and effects on immunity all raise the risk.
• Poor circulation in the legs and feet, such as peripheral artery disease (narrowing of the blood vessels supplying the limbs).
• Weakened immune system: for example from certain medications or medical conditions.
• Psoriasis and other nail disorders that alter the nail’s structure.
• Family history: susceptibility to fungal nail infection appears to run in some families.

Onychomycosis can spread from person to person indirectly — for example, through shared floors, towels, nail clippers, or footwear — although casual contact is a much less important route than a person’s own risk factors and foot environment.

Diagnosis

Onychomycosis diagnosis begins with a physical examination. A doctor — usually a dermatologist, a physician specializing in skin, hair, and nail conditions — inspects the affected nails and the surrounding skin, and asks about how the changes developed, footwear habits, previous nail injuries, and any medical conditions such as diabetes.

Because roughly half of all abnormal-looking nails are caused by something other than fungus, most guidelines recommend confirming the infection with laboratory testing before starting months of medication. Commonly used tests include:

• Nail clipping and scraping with microscopy: a small sample of the nail and the debris beneath it is taken painlessly. The sample is treated with a chemical (potassium hydroxide, often called a KOH preparation) that dissolves nail material so fungal elements can be seen under a microscope.
• Fungal culture: the sample is placed on a special growth medium in the laboratory to identify the exact fungus. Cultures are useful because they show which organism is responsible, but results can take several weeks and the test sometimes misses an infection that is truly present.
• Histopathology with special staining: a nail clipping is examined in a pathology laboratory using a stain (often called PAS staining) that highlights fungal structures. This is a sensitive way to confirm infection.
• Molecular (PCR) testing: in some laboratories, genetic tests can detect fungal DNA in the nail sample more quickly than culture.

Imaging tests such as X-rays are not needed to diagnose onychomycosis itself, although a doctor may occasionally order them if another problem — such as a bone abnormality under the nail — is suspected. Blood tests are not used to diagnose the infection, but your doctor may order baseline liver function tests before prescribing certain oral antifungal medicines, since these drugs are processed by the liver.

Confirming the diagnosis matters for two reasons. First, treatment is often long — several months or more — so it should target the correct problem. Second, conditions that mimic onychomycosis, such as nail psoriasis, need entirely different treatment.

Treatment options

Onychomycosis treatment aims to clear the fungus and allow a healthy nail to grow out. It is important to have realistic expectations from the start: nails grow slowly, so even successful treatment usually takes many months before the nail looks normal, and toenails can take a year or longer to fully regrow. Relapse or reinfection is possible even after apparently successful treatment.

Watchful waiting

Not every fungal nail infection has to be treated with medication. If the infection is mild, painless, limited to one nail, and mainly a cosmetic concern — and if the person is otherwise healthy — a doctor may discuss simply monitoring the nail, keeping it trimmed and filed, and focusing on foot hygiene to slow progression. However, untreated onychomycosis rarely resolves on its own and can spread, so this approach is generally reserved for selected cases and reviewed periodically.

Topical antifungal treatments

Medicated nail lacquers and solutions (for example, products containing ciclopirox, amorolfine, efinaconazole, or tavaborole, depending on the country) are applied directly to the nail, usually daily or weekly, often for many months. Topical treatment tends to work best for mild infections that involve only the surface or the outer part of the nail and do not reach the nail root. Because the medicine has difficulty penetrating a thick nail plate, cure rates with topical therapy alone are generally lower than with oral medication, and consistent long-term use is required.

Oral antifungal medication

Prescription oral antifungal tablets — most commonly terbinafine or itraconazole — are the standard treatment for moderate to severe onychomycosis and generally offer the best chance of cure. These medicines travel through the bloodstream into the nail bed, attacking the fungus from within. A typical course lasts about six weeks for fingernails and around twelve weeks for toenails, though schedules vary. Because oral antifungals can occasionally affect the liver and may interact with other medications, your doctor may order blood tests before or during treatment and will review your full medication list. These drugs are not suitable for everyone, including some people with liver disease.

Procedures and nail removal

Several procedures can support or replace medication in selected cases:

• Mechanical or chemical debridement: thinning and trimming the diseased nail, or softening it with a urea-based preparation, reduces the fungal load and can improve comfort and the penetration of topical medicines.
• Laser and light-based therapies: some devices are approved to temporarily improve the appearance of fungal nails. Evidence for lasting cure is more limited than for medication, so doctors often position these as an addition rather than a replacement.
• Surgical or chemical nail removal: in severe, painful, or repeatedly resistant infections, part or all of the nail can be removed, usually under local anesthesia (numbing of the area), often combined with antifungal treatment while the new nail grows. Surgery alone does not cure the infection, because the fungus can infect the regrowing nail.

The right combination depends on how many nails are involved, how deep the infection goes, the fungus identified, your overall health, and your preferences. Fungal nail infections are usually managed by dermatologists; at hospital groups such as Acibadem, this care is provided within the dermatology department, sometimes together with podiatric or diabetic foot care services when needed.

Living with onychomycosis and outlook

For most people, onychomycosis is a slow, persistent condition rather than a dangerous one. With appropriate treatment, many infections can be cleared, but honesty about the outlook is important: cure is not guaranteed, treatment takes months, and recurrence is relatively common — the same conditions that allowed the first infection can allow another. Older adults, people with very thick or long-standing infections, and people with circulation problems tend to have lower cure rates.

Day-to-day measures can make treatment more likely to succeed and reduce the chance of reinfection:

• Wash and thoroughly dry your feet daily, especially between the toes.
• Keep nails short, clean, and filed thin; use separate clippers for infected nails, or disinfect them after use.
• Change socks daily — more often if your feet sweat heavily — and choose breathable footwear.
• Alternate pairs of shoes so each pair can dry fully; antifungal powders or sprays for shoes may help.
• Wear sandals or flip-flops in communal showers, pools, and locker rooms.
• Treat athlete’s foot promptly, since skin infection often reseeds the nails.
• Avoid sharing towels, socks, shoes, or nail tools with others.

People with diabetes or poor circulation should take fungal nail infections seriously and have their feet checked regularly, because thickened, damaged nails and cracked skin can lead to sores and bacterial infections that heal poorly. If nail changes affect your confidence or comfort, that is a valid reason to seek care — cosmetic concerns are a recognized part of this condition’s burden.

Frequently asked questions

What is onychomycosis in simple terms?

Onychomycosis is a fungal infection of a fingernail or toenail. Microscopic fungi grow in or under the nail and feed on its protein, causing the nail to become discolored, thick, brittle, or misshapen over time. It is very common, affects toenails more often than fingernails, and becomes more frequent with age.

Can onychomycosis go away on its own?

In most cases, no. Fungal nail infections rarely clear without treatment, and they usually progress slowly, sometimes spreading to other nails or to the surrounding skin. Mild cases may be monitored rather than treated, but if you want the infection cleared, medication or other treatment supervised by a doctor is generally needed.

How serious is onychomycosis?

For most healthy people it is primarily a cosmetic and comfort problem rather than a serious threat. However, in people with diabetes, poor circulation, or weakened immunity, a damaged nail can lead to skin breaks and bacterial infections such as cellulitis (a spreading infection of the skin and tissue beneath it), which can be serious. These groups should not ignore fungal nail changes.

How long does onychomycosis treatment take?

Treatment courses are long because nails grow slowly. Oral antifungal medication is often taken for about six weeks for fingernails and around twelve weeks for toenails, while topical lacquers may be used for many months. Even after the fungus is cleared, the damaged part of the nail must grow out and be replaced by healthy nail, which can take up to a year or more for toenails.

What are the first symptoms of onychomycosis?

Early onychomycosis symptoms are often subtle: a small white, yellow, or brown spot or streak at the tip or edge of the nail, slight thickening, or a bit of crumbly debris under the nail. Pain is uncommon at first. Because other conditions can look similar, a doctor can confirm whether the change is really fungal with a simple nail sample test.

Is onychomycosis contagious?

The fungi that cause onychomycosis can spread indirectly — for example through shared floors in pools and locker rooms, shared towels, or shared nail tools — and the infection can spread from your own skin (athlete’s foot) to your nails. Direct person-to-person spread through casual contact is less common. Good foot hygiene and not sharing personal items reduce the risk.

Can onychomycosis come back after treatment?

Yes, recurrence and reinfection are relatively common, even after successful treatment. The same risk factors — sweaty feet, communal wet areas, untreated athlete’s foot, older shoes harboring fungal spores — can allow a new infection. Continuing preventive habits after treatment, and treating any skin fungal infection promptly, lowers the chance of the problem returning.

When to see a doctor

It is reasonable to see a doctor — typically a dermatologist — whenever a nail becomes discolored, thickened, or distorted and does not improve, especially before starting any long course of over-the-counter treatment, since testing can confirm whether fungus is really the cause. Seek medical attention promptly if you notice any of the following warning signs:

• Pain, redness, warmth, or swelling around the nail or spreading up the toe or foot, which may signal a bacterial infection.
• Pus or discharge coming from around the nail.
• Fever or feeling generally unwell together with a red, painful toe or foot.
• You have diabetes, poor circulation, or a weakened immune system and develop any new nail change, sore, or skin break on the foot — even a minor one.
• A dark streak or spot under a nail that is new, growing, or not clearly explained by injury, since rare but serious conditions such as melanoma (a skin cancer) can appear under the nail and need urgent evaluation.
• Rapidly worsening nail damage, bleeding under the nail, or a nail that is painful enough to limit walking.
• No improvement or worsening despite completing a prescribed course of antifungal treatment.

Early evaluation makes diagnosis easier, keeps treatment shorter and more effective, and helps prevent complications — particularly for people whose overall health puts their feet at higher risk.