July 1, 2025, 8:50 am | Read time: 7 minutes
If fingernails or toenails turn yellow to light brown and thicken, it likely indicates a nail fungus. It’s not a pleasant sight–but at least it’s usually painless and doesn’t itch. However, the infection shouldn’t be taken lightly. FITBOOK editor Michel Winges explains how to identify nail fungus early, what truly helps against it, and the measures you can take to effectively prevent it.
Nail fungus usually doesn’t just appear out of nowhere; it is often preceded by another fungal infection, such as athlete’s foot. The tiny pathogens enter through small injuries or cracks in the skin and then infect the nail. Toenails are particularly at risk: The environment there is often warm and moist, providing ideal conditions for fungi. The nail may turn yellowish to brownish, thicken, become brittle, and in advanced cases, partially detach. Nail fungus is sometimes considered merely a cosmetic issue, but if left untreated, it can progress and affect surrounding tissue. The later the treatment begins, the longer it may take.1
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Overview
How to Recognize Nail Fungus?
Nail fungus (medically known as “onychomycosis”) often begins subtly—and that’s what makes it so insidious. Initially, there is only a slight discoloration, often at the outer edge of the nail. But over time, the changes become more pronounced. Here is an overview of the most common symptoms:
- Discoloration: The nail turns yellowish, whitish, or brownish. Initially spotty, later more widespread.
- Thickening: The nail plate becomes thicker and partially lifts from the nail bed.
- Brittleness: The nail splits, becomes porous, or starts to crumble.
- Dull Shine: Healthy nails have a slight shine. Fungus-infected nails often appear matte and translucent.2
- Detachment: In advanced cases, the nail may partially or even completely detach.
Toenails, especially the big toe, are most commonly affected. Fingernails are less frequently infected but are also at risk, particularly in people with frequent water exposure or small injuries around the nail.
Important: The earlier the treatment begins, the better the fungus can be contained. If in doubt, medical advice should be sought. A definitive diagnosis is usually made through a laboratory test.
These Variants Exist
Distal Lateral Subungual Onychomycosis
By far the most common form. The fungus initially infects the skin around the nail, such as at the nail edge or under the nail tip, and then works its way into the nail plate from below. It slowly spreads there, making the nail soft, brittle, and yellowish.
Proximal Subungual Onychomycosis
Much rarer but particularly insidious: In this variant, the fungus attacks directly at the nail root, where the nail is formed. From there, the infection spreads across the entire nail plate. This form occurs more frequently in people with weakened immune systems.
White Superficial Onychomycosis
In this form, the infection is limited to the top layer of the nail plate. The fungus (Trichophyton is usually the cause here) grows exclusively on the top layer of the nail. The result: The nail shows whitish spots or appears milky discolored. This variant is considered relatively easy to treat.
Total Onychodystrophy
In this stage, the fungus has destroyed the entire nail—including the nail bed and root. The nail plate is completely damaged, brittle, discolored, or even completely detached. Treatment is particularly lengthy and requires a lot of patience; sometimes, complete removal of the nail is the only option.
Causes
Walking barefoot without flip-flops in the swimming pool, sauna, or shower area of the gym—and it happens: Fungi, which are just waiting on warm, damp floors to find new “host feet,” have an easy time. They don’t need much: a small injury, a fine crack in the nail, or some softened skin is enough for them to settle in.
Nail fungus is usually caused by so-called “dermatophytes.” These are fungi that thrive on skin, hair, and nails. But yeast or mold can also be culprits. The pathogens penetrate the nail and multiply where they are hardly disturbed: under the thick horn plate. Toenails are particularly affected because a warm, moist climate often prevails there due to shoes, socks, and sweat. An existing athlete’s foot can also serve as an entry point for a subsequent nail infection.
Also interesting: The different forms of skin fungus and their symptoms
Frequency in Old Age?
Nail fungus occurs more frequently with age. Studies show that the risk increases significantly with age. In the age group over 65, a prevalence of up to 50 percent is described.3 The reason is that blood circulation decreases with age, and nails grow more slowly. This makes them more susceptible to fungal colonization. Additionally, diseases such as diabetes or vascular diseases increase with age and can weaken the immune system. Foot care also becomes more difficult as mobility and vision decline, so the fungus often goes unnoticed for a long time.
Diagnosis
If the nail shows discoloration, a brittle structure, or unusual thickening, a fungal infection may be present. Many immediately think of nail fungus and are often right, but not always. Psoriasis, eczema, or injuries can also cause similar changes in nails. To be sure, more than just a look at the external appearance is needed. The first step is to visit a dermatology practice. The dermatologist examines the affected nail closely and checks for typical signs such as color, texture, and spread. Usually, a sample of the infected nail material is then taken and examined in the lab. Depending on the method, it takes a few days to weeks for a result.
- Direct Microscopy: Here, the material is examined under a microscope for fungal structures.
- Fungal Culture: An attempt is made to “cultivate” the pathogen to determine which type of fungus is responsible for the infection.
- PCR Test: Modern labs use molecular genetic methods to detect fungal DNA, which is particularly precise but not standard everywhere.4
Identifying the exact fungus is important because not every drug works against every pathogen. Thus, determining the fungus lays the foundation for targeted treatment.
Treatment
Nail fungus is persistent but treatable. Since nails grow slowly, it can take several months for a healthy nail to fully regrow. The key to successful therapy is the right combination of medication, patience, and consistent application. A spontaneous resolution without treatment is generally not expected.
- Topical Treatment with Lacquer or Cream: If the infection is still limited, affecting less than 50 percent of the nail plate and a maximum of three nails, a topical treatment is usually sufficient. Special antifungal lacquers or creams are used, which are applied regularly. The nail should be roughened or pretreated with a urea ointment to allow the active ingredients to penetrate better.5,6
- Systematic Therapy with Tablets: For more severe or advanced infections, such as when multiple nails are affected or the fungus has penetrated deep into the nail bed, experts recommend a combination of topical and oral treatment.7 Antifungal tablets like terbinafine or itraconazole are used to fight the pathogen from the inside out. The medication is taken for several weeks to months and should be monitored by a doctor due to possible side effects.
- Laser Therapy: A newer method is laser therapy, where the infected nail is irradiated with infrared light. The goal is to destroy the fungal structures without damaging the nail. The effectiveness of this method is not yet conclusively determined according to studies.8
- Home Remedies: Vinegar, tea tree oil, or baking soda are often recommended as home remedies for nail fungus. However, their effectiveness is not scientifically proven. They can at best be supportive but do not replace medical treatment.
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How to Prevent?
The risk of nail fungus can be prevented through simple hygiene measures. It starts in the swimming pool or sauna: Walking barefoot through wet areas like showers or changing rooms increases the risk of infection. Therefore, the rule is: Do not walk barefoot in public showers, changing rooms, or spa areas.
Other things to pay attention to in everyday life:
- Keep feet dry: Dry thoroughly after showering, especially between the toes.
- Change socks daily: Preferably made of breathable materials like cotton.
- Ventilate and disinfect shoes: Regularly air out sports shoes and, if necessary, treat with antifungal spray.
- Nail care: Do not cut nails too short, and avoid sharp corners or injuries to the nail bed.
- Use personal tools: Nail scissors, files, etc., should only be used by one person and cleaned regularly.
- Strengthen the immune system: A well-nourished body offers less surface for the fungus to attack.
And very important: Take athlete’s foot seriously! It is often the entry point for a nail infection. If you notice itching, redness, or scaling on your feet, you should act early.