Fungal Nail Infection (Onychomycosis) - Symptoms, Causes & Treatment
By ScanSkinAI Editorial Team✓ Reviewed for medical safetyLast updated June 2026
A fungal infection of the toenails or fingernails that causes thickening, discoloration, and crumbling of the nail. It's common and can be difficult to treat.
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Quick Answer
A fungal nail infection, or onychomycosis, occurs when fungi invade your toe or finger nails. This causes the nail to become thick, discoloured, and brittle or crumbly. These infections thrive in warm, moist environments like sweaty shoes or locker rooms. While common, they can be stubborn and difficult to clear up. Treatment usually involves oral or topical antifungal medications prescribed by a doctor. Although not usually dangerous, you should seek medical advice if the affected nail becomes painful, significantly distorted, or if you have an underlying condition like diabetes.
Symptoms
- Thickened nails
- Yellow, brown, or white discoloration
- Brittle, crumbly nails
- Distorted nail shape
- Debris under nail
- Slight odor
Causes & Risk Factors
- Dermatophyte fungi
- Yeast
- Molds
- Warm, moist environments
- Nail injury
- Age
Treatment & Management
- Oral antifungals (terbinafine, itraconazole)
- Topical antifungals (less effective)
- Medicated nail polish
- Laser treatment
- Nail removal in severe cases
When to See a Doctor
If nails become significantly thickened, painful, or if you have diabetes
Frequently Asked Questions
How do I know if I have a fungal nail infection?
The most common signs are changes in how your nail looks and feels. You might notice the nail becoming unusually thick, brittle, or crumbly. It often changes colour, turning yellow, brown, or white. The nail shape might become distorted, and you may find debris building up underneath it. You might also notice a slight, unpleasant odour coming from the nail.
How did I get nail fungus?
Fungal nail infections are usually caused by dermatophyte fungi, though yeasts and moulds can also be the culprit. These organisms thrive in warm, moist environments. You can easily pick up the fungus by walking barefoot in public showers or swimming pool locker rooms. Wearing tight, sweaty shoes for long periods or having a minor nail injury also makes it easier for the fungus to take hold and grow.
What is the best way to get rid of a fungal nail infection?
Unfortunately, nail fungus can be stubborn. The most effective treatments are usually prescription oral antifungal tablets, such as terbinafine or itraconazole. Topical treatments like medicated nail polishes are available but tend to be less effective on their own. In some cases, doctors might suggest laser treatment or, for severe and painful infections, completely removing the affected nail to allow a healthy one to grow back.
How long does it take to cure toenail fungus?
Clearing a fungal nail infection requires patience. Even after the fungus is destroyed by medication, the nail will still look damaged until a completely new, healthy nail grows out. For fingernails, this can take around six months. For toenails, it often takes twelve to eighteen months for the nail to fully replace itself. It is important to complete your treatment course to prevent the infection from returning.
When should I see a doctor about my thick toenails?
While mild fungal infections might just be a cosmetic annoyance, you should visit a healthcare professional if the nail becomes significantly thickened, distorted, or painful. It is especially important to see a doctor promptly if you have diabetes or a weakened immune system. Diabetes can reduce blood flow and nerve sensation in your feet, meaning a minor nail infection could quickly develop into a more serious foot complication.
How can I stop nail fungus from coming back?
To prevent reinfection, keep your feet as clean and dry as possible. Wear moisture-wicking socks and choose breathable shoes, making sure to alternate your footwear so they can dry out completely between uses. Always wear flip-flops in public showers, locker rooms, and around pool areas. Finally, keep your nails trimmed straight across and disinfect your nail clippers after each use to stop the fungus from spreading.
Is it a fungal infection or just nail trauma?
It can be surprisingly hard to tell the difference. Both nail fungus and physical trauma (like dropping something on your foot or wearing shoes that are too tight) can cause the nail to thicken, lift, and change colour to yellowish-brown or black. However, trauma usually happens suddenly and affects a specific injured nail, whereas a fungal infection often starts at the nail edge and slowly spreads over time.
How can ScanSkinAI help with a fungal nail infection?
ScanSkinAI can analyze photos of your nails to help identify visual features commonly associated with fungal infections, such as thickening and discoloration. However, it is important to remember that ScanSkinAI is a screening aid, not a diagnostic tool. Since conditions like psoriasis or nail trauma can look very similar to a fungal infection, you should always consult a doctor for a professional diagnosis and appropriate treatment plan.
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Medical References
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Medical Disclaimer: This information is for educational purposes only and is not intended as medical advice. The content on this page should not be used to diagnose or treat any health problem. Always consult with a qualified healthcare professional for proper medical evaluation, diagnosis, and treatment of your condition.