Key Takeaways
My yellow nails are because of an injury, fungal infection, stain from polish or something else? What does nail fungus look like? These are some of the common questions I receive almost daily. If you know the answer it will help you solve the problem as well and might save you months of effort.
About 10% of people worldwide suffer from onychomycosis, which increases to 50% in individuals over 70. But research indicates that 50%-60% of those with abnormal-looking nails do not have fungus. They have trauma or psoriasis or are caused by another condition (VCU Health). Antifungals are ineffective in treating psoriasis. It is also a bad idea to use steroids to treat a fungal infection. The onchomycosis diagnosis is very important.
For over 20 years, Imperial Feet Products has been working with foot care specialists on this matter. Today, in this session I will tell you how to use your eyes, the first diagnostic tool.
What Is a Fungal Nail Infection? Causes and How It Develops
Onychomycosis is a fungal infection of the nail plate, nail bed or both. It represents around 50% of all nail disorders in adults, the most common nail disease worldwide.
Dermatophytes are responsible for 90% of lesions, primarily Trichophyton rubrum and T. mentagrophytes. Fingernails are more common to get yeast infections (Candida). Fungi invade through the distal free edge, lateral nail fold or a minute defect in the skin. These include nail trauma and separation of the nail from the nail bed.
Toenails are more susceptible than fingernails, as they are growing at half the rate of fingernails, and are in shoes for hours every day, in hot, moist conditions.
Progression: Discoloration begins at the nail tip → spreads inward → thickens → nail plate deforms → total nail dystrophy in severe cases.
Fungal Nail Symptoms? 7 Key Visual Signs to Spot
Sign 1: White, Yellow, Brown or Green Discoloration | Early Signs of Nail Fungus
If you notice a change in the colour of your nails in this order, the nail changes from white to yellow to brown to green. This is the first sign.
The first symptom is nearly invariably discoloration, which begins as a little area beneath the nail tip.
Colour guide: White spot under toenail indicates White Superficial Onychomycosis. Yellow to yellow-brown nails indicate a classic DLSO dermatophyte infection. Dark brown indicates a deeper infection, especially in darker skin tones. Green to black indicates a secondary bacterial co-infection (Pseudomonas aeruginosa) (AAD, 2024)..
Common Misread: Yellow nails may be from polish staining or from smoking and do not result in thickening or changes in the nail plate. It will fade evenly but yellow toenail fungus discolouration doesn't. Learn how to get rid of yellow toenails, check the full guide.
Sign 2: Nail Thickening | Why Fungal Nails Become Hard to Trim
The fungus infects the nail plate and is able to devour keratin and replace it with hyphae and debris. Normally the thickness of the toenail is 0.5 - 1 mm, and in advanced fungal nails it can reach to 2-4 mm.
If one of the nails is more brittle and harder to cut than the others, probably fungal involvement. Thickening may appear as brown instead of yellow discolouration in darker skin tones.
Sign 3: Brittle, Crumbling and Ragged Nail Edges
During the degradation of the keratin matrix the nail loses its shape. The edges fall apart, crumble and crack. The surface is not shiny (glossy) but chalky and dull.
The fungus can cause damage to the keratin in your nails as it grows. This makes your nail weak. You may begin to experience splitting, cracking or crumbling of your nails.
A diagnostic feature is the presence of white or yellowish powdery debris under the nail, consisting of fungal hyphae, keratin fragments and skin cell debris. Don't forcibly file a nail collapsing without a treatment plan, as this may spread spores to other nails.
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Sign 4: Nail Separation From the Nail Bed | Onycholysis
As the fungus grows, it helps to raise the nail plate off the nail bed which makes the nail bed more favorable for infection. The separated area is white or yellow and extends from the free edge towards the cuticle as an opaque patch.
Typically not painful, even when the condition becomes serious, unless there is secondary bacterial infection.
One difference between psoriasis and psoriatic onycholysis is that there may be a salmon pink oil-drop patch under the nail. The absence of this warm colour leads to more uniform white or yellow opalescence in fungal onycholysis. To make a good comparison, take a look at psoriasis nail or fungal nail — how to tell the difference.
Sign 5: Subungual Debris | Build-Up Under the Nail Plate
The chalky, powdery material under the nail plate is a response to invasion and an overproduction of keratin by the nail bed. The tip of the nail is lifted up from below.
This debris is infected with live fungal spores. Do not use a scraper; wash hands and sanitize tools immediately afterwards.
Sign 6: Shape Distortion and Misshapen Nails
Damage to the nail matrix (the area in which nails grow) can cause them to curve inwards or outwards. This is an indication of late-stage infection.
If the only symptom of fungal disease is shape distortion, it is more likely to be due to proximal subungual onychomycosis or nail trauma. Grossly distorted nails can be restored but it will take 9-12 months to regenerate them completely.
Sign 7: Odour From the Affected Nail
The presence of foul odour indicates secondary bacterial co-infection, usually Pseudomonas aeruginosa or Staphylococcus aureus. Green nail syndrome is characterised by strong smell and green-black colour. It requires antifungal and antibacterial therapy. If the nail shows both colour change and odor, it is essential to be seen by a professional.
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How to Recognize Nail Fungus| The 4 Clinical Types of Fungal Nail
| Type | Abbreviation | Where It Starts | Key Visual Signs | Main Cause | Difficulty |
|---|---|---|---|---|---|
| Distal Lateral Subungual Onychomycosis | DLSO | Under nail tip/sides | Yellow-brown + thickening from tip to base | T. rubrum | Moderate |
| White Superficial Onychomycosis | WSO | Nail plate surface | White powdery patches, scraped off easily | T. mentagrophytes | Easiest |
| Proximal Subungual Onychomycosis | PSO | Near nail base/cuticle | White opacity near lunula, spreading distally | T. rubrum (immunocompromised) | Difficult |
| Total Dystrophic Onychomycosis | TDO | Entire nail | Complete destruction, massively thickened, crumbling | Chronic DLSO/PSO |
Most severe |
Nail Fungus vs Nail Psoriasis vs. Trauma: How to Tell the Difference
| Feature | Fungal Nail | Nail Psoriasis | Nail Trauma | Bacterial (Pseudomonas) |
|---|---|---|---|---|
| Primary colour | Yellow, white, brown | Yellow-brown, oil-drop salmon patch | Dark purple → yellow/brown | Green or black |
| Nail surface | Dull, chalky, crumbling | Pitting (small dents), ridges | Often smooth but discoloured | Smooth but discoloured |
| Onset speed | Gradual (weeks–months) | Gradual | Sudden after injury | Rapid (days) |
| Number of nails | 1–2 initially, spreads | Often multiple | Usually 1 nail | Usually 1 nail |
| Odour | Mild or absent | Absent | Absent | Strong — key differentiator |
| Contagious? | Yes | No | No | Limited |
| Do NOT treat with | Steroids (worsens) | Antifungals (ineffective) | Antifungals (waste of time) | Antifungals alone |
| Stage | Visual Appearance | Timeline | What to Do |
|---|---|---|---|
| Stage 1 — Early | Small white/yellow spot at nail tip; plate otherwise normal | Weeks 1–4 | Start nail mycosis solution immediately — easiest to treat |
| Stage 2 — Progressing | 25–50% discoloured; mild thickening; surface dulling | Months 1–3 | Twice-daily treatment + file + shoe spray |
| Stage 3 — Established | 50–75% affected; significant thickening; brittle edges; possible separation | Months 3–6 | Intensive topical + podiatry consultation |
| Stage 4 — Advanced | Entire nail; grossly thick and deformed; heavy debris; total separation | 6+ months | GP/podiatrist evaluation; oral terbinafine often needed |
Fungal Nail Recognition and Treatment Globally: Country Comparison
| Country | Prevalence | Most Common Presentation | Diagnostic Access | Typical Stage at Diagnosis | Imperial Feet |
|---|---|---|---|---|---|
| Netherlands | ~9% adults | Yellow DLSO | Podiatry + GP | Early-moderate | Yes (HQ) |
| USA | ~14% adults | Yellow-brown DLSO | Podiatrist/dermatologist | Moderate (Stage 2–3) | Yes |
| UK | ~10% adults | Yellow-white DLSO | GP + podiatry | Moderate | Yes |
| India | ~18% adults | Brown-black (darker skin tones) | Dermatologist | Often late (Stage 3–4) | Limited |
| Germany | ~12% adults | Yellow DLSO | Apothecary + dermatologist | Moderate-early | Yes |
| Australia | ~10% adults | Yellow-white DLSO/WSO | Podiatry + pharmacy | Moderate | Yes |
| Brazil | ~15% adults | Yellow-brown DLSO | Dermatologist | Often late | Limited |
| Japan | ~6% adults | White WSO + Yellow DLSO | Dermatologist (Rx-only) | Variable | No |
When to See a Doctor for Nail Fungus: 6 Signs Not to Ignore
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Green, black or foul-smelling nails bacterial co-infection (must be treated with prescription).
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Diabetes: If nails change, see a professional, if there is poor circulation, then infection will progress without warning signs.
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Multiple nails involved in an infection. Oral antifungal medications may be necessary for more extensive infections.
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Continued topical treatment for 3 months without improvement. It indicates that there is a deep infection or misdiagnosis
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If the fold around the nail is painful, red or enlarged, it may develop into a subsequent bacterial infection (paronychia) that needs medical attention
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Nail psoriasis is suspected or known to be associated with other diseases.
Recognise the Signs? Here's How to Start Treatment
Stages 1-2: The solution for nail mycosis is the first line professional formula. Tea tree oil, the penetration power, is carried by jojoba oil, and tolnaftate, an FDA-recognized OTC antifungal. Twice-daily application after light filing.
Stage 3 onward: The full fungal nail treatment system includes the antifungal shoe spray. 80% of people who get recurrent nail fungus infections have it due to contaminated shoes. It's half a treatment to treat the nail but not the shoe.
Toenails grow 1.5mm per month. After regular treatment for 4-8 weeks, a healthy new nail will grow in at the base. This infected nail will then grow out in 6-12 months. Learn about the nail fungus treatment spectrum and the antifungal foot treatment products to follow for a complete treatment.
Frequently Asked Questions About Recognising Nail Fungus
What Does Early Stage Nail Fungus Look Like Before It Spreads?
The first sign of a nail fungus is usually a small white or yellow spot that develops under the tip of the nail, typically at the side of the nail. The thickening and crumbling of the nail plate itself may not have occurred. The most treatable stage is this one. Most people just ignore the first mark as a stain. While implementing early nail fungus treatment will significantly decrease overall recovery time.
Is It Nail Fungus or Just a Bruised or Damaged Toenail?
Trauma after a specific injury presents suddenly with dark red or purple color progressing to a yellow or brown discoloration, usually in one nail. Fungal nail is a slow-developing condition, usually beginning with a white/yellow spot at the very tip that progresses slowly towards the base over days or weeks. If a nail is thickening and has begun to spread up towards the cuticle, treat for fungus.
Can You Have Nail Fungus Without Yellow or Obvious Discoloration?
Yes. During this stage, the condition is known as White Superficial Onychomycosis. It is characterized by white, powdery lesions on the top of the nails, which can be scraped off. If there are early infections, they may show only slight dullness and then the obvious colour change occurs. Discolouration is usually brown and not yellow on darker skin tones.
How Is Nail Fungus Officially Diagnosed by a Podiatrist or Doctor?
KOH test: Nail scraping in potassium hydroxide solution fungal hyphae seen under microscope within 30–60 minutes. Fungal culture: takes two to six weeks to identify the particular organism. The laboratory confirms psoriasis and dismisses mimics of psoriasis as well as trauma if topical treatment does not work after 3+ months.
Can Nail Fungus Spread to Other Nails or Other People?
Yes, to both. Nail fungus spreads to adjacent nails by sharing footwear settings; to surrounding skin by athlete's foot, and to household members through contaminated floors, bath mats, towels and nail tools. In treatment: wear antifungal shoe spray all day, wash towels separately, sanitize nail implements after each use and wear flip-flops in common bathrooms.