Fungal Nail Infection: Causes, Symptoms and How to Treat It

If you've noticed a nail turning yellow, thickening, or crumbling at the edges, you may have a fungal nail infection. Also called onychomycosis, it's one of the most common nail conditions we see in general practice and podiatry. Prevalence estimates range from 1% to 8%, and the incidence is increasing (Bodman et al., 2025). Hong Kong's warm, humid climate makes it more common than many people realise, affecting up to 26.8% of the population. This means roughly one in four individuals may experience a fungal nail infection at some point (Chan HL, et al., 2014).

The good news: fungal nail infections are treatable. The less welcome news: treatment takes patience, often months, and the condition won't resolve on its own. Here's what you need to know about recognising, treating, and preventing it.

What is a fungal nail infection?

A fungal nail infection happens when fungi invade the nail, feeding on keratin, the protein that gives nails their hard surface. Toenails are affected far more often than fingernails because these fungi thrive in the dark, moist and stuffy environment inside shoes (Harvard Health, 2024).

Common dermatophytes causing Fungal nail

Trichophyton rubrum
Trichophyton mentagrophytes
Epidermophyton floccosum

These dermatophytes are identified in 90% of the toenail and 50% of the fingernail onychomycosis (Bodman et al., 2025), with yeasts and moulds making up the rest.

Are you at risk of fungal nail infection?

Toenail fungus can be caused by several different types of fungi (Harvard Health, 2024), but certain factors raise your risk significantly:

Athlete's foot. An asymptomatic, dry hyperkeratotic tinea pedis usually precedes onychomycosis (Bodman et al., 2025), untreated athlete's foot is the most common gateway.
Age. Nails grow more slowly and thicken with age, giving fungi more time to establish. (Bodman et al., 2025)
Diabetes and immunodeficiency. Risk factors include aging, diabetes, tinea pedis, psoriasis, immunodeficiency, and living with family members with onychomycosis (Bodman et al., 2025).
Warm, humid environment. Hong Kong's subtropical climate, communal living spaces, and enclosed footwear create ideal conditions.
Shared surfaces. Hotel carpets, public showers, and pool decks can culture causative organisms (Bodman et al., 2025).

Fungal Nail Symptoms by stages

You may have a fungal nail infection if your nail is brittle, discoloured or thicker than usual (NHS, 2024). Here's what to look for as the infection progresses:

Early stage

A small white or yellowish spot near the nail tip or edge
The nail looks slightly dull compared to your other nails
No pain or thickening yet

This is the best window for treatment, before the infection reaches the nail bed.

Moderate stage

It typically turns yellow or brown and becomes thick and overgrown (Harvard Health, 2024)
The nail becomes crumbly or ragged at the edges
Debris collects under the nail, sometimes with an unpleasant odour

Advanced stage

The nail lifts away from the nail bed
Pain or discomfort when wearing shoes
Infection may spread to adjacent nails

It is important to get a proper diagnosis. "Almost half of the abnormal-appearing toenails are not mycotic" (Bodman et al., 2025), psoriasis, trauma, and bacterial infections can mimic fungal nails. Mycological testing plays an essential role in establishing an accurate diagnosis.

Traumatic injury is a common precursor to a fungal nail infection. A one off knock or bang, or repetitive micro-trauma to the nail caused by pressure from footwear can cause the ‘seal’ between the skin and nail to become broken. This allows a portal of entry for the fungus to get under the nail. It therefore becomes very difficult to keep clean and the fungus can easily spread.

Treatment options for Fungal nails

There's no overnight fix, but several treatments have strong evidence behind them.

Topical antifungal nail solutions

For mild or early-stage infections, a topical antifungal solution (also called nail lacquer or paint) is applied directly to the nail. These need to be used for 6 to 12 months (NHS, 2024). Mycological cure rates for topical therapy are 55% with efinaconazole and 36% with tavaborole or ciclopirox (Bodman et al., 2025), so they're a reasonable first step.

Oral antifungal medication

The most effective treatments for fungal nails are systemic antifungals. (Bodman et al., 2025). You may need to take antifungal tablets for up to 6 months (NHS, 2024), with mycological cure rate ranging from 48% to 76% (Depending on the antifungals used) (Bodman et al., 2025). These are however contraindicated for people with liver or kidney disease, pregnant or nursing mothers, people taking statins or immunosuppressants (Herrick EJ., et al. 2024, Prabhu, et al., 2017).

Your GP/podiatrist will typically request a nail sample to confirm the type of infection and blood tests before treatment and during treatment to monitor liver function (NHS, 2024).

Combination therapy

Combining oral treatment with adjunctive approaches, such as topical antifungals, regular nail debridement, or chemical nail avulsion, may lead to improved outcomes compared with systemic therapy alone (Bodman et al., 2025).

Nail removal

In more advanced cases, severely affected nails may need to be removed (NHS, 2024). This is a minor procedure which can be performed by a Podiatrist under local anaesthetic and is typically considered when other treatments have not been effective.

Prevention tips

Prevention is far easier than treatment. Simple habits make a real difference:

Keep nails trimmed short and feet clean and dry
Wear clean socks daily and choose breathable footwear, especially in Hong Kong's humid months
Wear flip-flops in showers at the gym or pool" (NHS, 2024)
Treat athlete's foot promptly, the same fungi spread to nails
Don't share nail clippers, files, or towels
Air out shoes between wears
If you have diabetes or circulation problems, schedule regular foot checks

Frequently asked questions

1. Are fungal nail infections contagious?

Yes. The fungi spread through shared surfaces, direct contact, and household items like towels and nail clippers. You can also spread the infection from one nail to another. Wearing footwear in communal wet areas and not sharing personal foot-care items significantly reduces your risk.

2. Is laser treatment effective for fungal nails?

Laser therapy is an area of growing interest. Some studies report mycological cure rates of around 63% for Nd:YAG lasers and 74% for CO2 lasers (Ma W, et al, 2019), but the overall evidence remains mixed and it is not currently included in standard NHS treatment guidelines.

The 1.064-nm diode laser is an effective and safe option for the treatment of onychomycosis. Of note, the combination with topical antifungals will increase overall treatment efficacy and reduce the time to healing (Weber GC, et al., 2018).

Laser may be worth considering if you cannot tolerate oral antifungals (due to liver concerns or drug interactions), prefer a non-systemic approach, or as part of a combination strategy. Your podiatrist can advise whether it's appropriate for your case.

3. Will a fungal nail infection heal on its own?

Toenail fungus rarely resolves on its own (Harvard Health, 2024). Left untreated, it is typically a chronic, long-lasting condition that can gradually worsen, affecting more of the nail over time (Harvard Health, 2024).

Seeking treatment early from GP/podiatrist not only helps limit disease progression but may also lead to a shorter treatment course and better overall outcomes.

4. How long does it take to cure a fungal nail infection?

The infection is cured when you see healthy nail growing back at the base (NHS, 2024). A full toenail takes 12 to 18 months to grow out, so patience and is essential (ScienceInsights, 2025). A dedicated approach to regular application of topical medication is required to achieve optimal treatment results.

5. Should you see a GP or a podiatrist for a fungal nail infection?

Your GP can assess the nail, arrange lab testing, and prescribe oral antifungals.

A podiatrist specialises in foot and nail health, offering expert diagnosis, debridement, laser therapy, and ongoing care.

For mild cases, start with your GP or pharmacist. For persistent or recurring infections, a podiatrist referral gives you the widest range of treatment options.

When to see a podiatrist

Many people with fungal nail infections start with pharmacy treatments, which is appropriate for mild cases. However, it’s important to seek professional advice if the condition does not improve or becomes more severe.

A podiatrist can help you remove any loose parts of the nail and clear away the visible fungal debris. This is a useful adjunct therapy which allows the topical antifungal solution to penetrate the nail more effectively.

Consider booking an appointment with your podiatrist if:

Over-the-counter treatments haven't improved things after several months
The infection is severe and treatment has not worked (NHS, 2024)
The infection has spread to multiple nails
You have diabetes, as foot problems can become more serious
You have a weakened immune system

Early assessment can help guide appropriate treatment and prevent the infection from worsening.

Heidi Corcoran

Podiatry

Heidi was head of the Podiatry department in the Hospital Authority for over 20years and speaks Cantonese. She founded the first internationally recognised podiatry association in SE Asia, and became President of FIP, the global federation of national podiatry associations. As a member of the expert consensus group IWGDF and Director of D-Foot International, she developed guidelines for best practice in diabetic foot care. Heidi’s research in diabetes, vascular, renal disease, telemedicine and elderly footcare has been widely published. Heidi led clinical teaching for medical, nursing and allied health colleagues at CUHK, also mentoring podiatry scholars and new graduates. She is a passionate advocate for the benefits of podiatry care.

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References

Bodman, M.A., Syed, H.A. and Krishnamurthy, K. (2025). 'Onychomycosis'. StatPearls. Available at: https://www.ncbi.nlm.nih.gov/books/NBK441853/ (Accessed 22 June 2026)
Harvard Health. (2024). 'Toenail Fungus (Onychomycosis)'. Harvard Health Publishing. Available at: https://www.health.harvard.edu/a_to_z/toenail-fungus-onychomycosis-a-to-z (Accessed 22 June 2026)
NHS. (2024). 'Fungal nail infection'. NHS. Available at: https://www.nhs.uk/conditions/fungal-nail-infection/ (Accessed 22 June 2026)
Chan, HH, Wong, ET and Yeung, CK (2014) ‘Psychosocial perception of adults with onychomycosis: a blinded, controlled comparison of 1,017 adult Hong Kong residents with or without onychomycosis’, BioPsychoSocial Medicine, 8, 15. doi:10.1186/1751-0759-8-15.
ScienceInsights (2025) ‘How Long Does It Take for Your Toenails to Grow?’. Available at: https://scienceinsights.org/how-long-does-it-take-for-your-toenails-to-grow/ (Accessed: 24 June 2026).
Ma, W., Si, C., Kasyanju Carrero, L.M., Liu, H., Yin, X., Liu, J., Xu, Y. and Zhou, B. (2019) ‘Laser treatment for onychomycosis: A systematic review and meta-analysis’, Medicine, 98(48), e17948. doi:10.1097/md.0000000000017948.
Herrick, E.J. and Patel, P. (2024). 'Antifungal ergosterol synthesis inhibitors.' StatPearls. Available at: https://www.ncbi.nlm.nih.gov/books/NBK551581/ [Accessed: 26 June 2026].
Prabhu, S.S. and Sankineni, P. (2017). 'Managing dermatophytoses in pregnancy, lactation, and children.' Clinical Dermatology Review, 1(Suppl 1), pp. S34 to S37. Available at: https://doi.org/10.4103/CDR.CDR_29_17.
Weber, G.C., Firouzi, P., Baran, A.M., Bölke, E., Schrumpf, H., Buhren, B.A., Homey, B. and Gerber, P.A. (2018). 'Treatment of onychomycosis using a 1064-nm diode laser with or without topical antifungal therapy: a single-center, retrospective analysis in 56 patients.' European Journal of Medical Research, 23, p. 55. Available at: https://doi.org/10.1186/s40001-018-0340-y.