Nail Fungus: What Causes It, and What Treatment Can — and Can't — Do
Updated: Oct 28
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 17, 2026
Nail fungus (onychomycosis) starts as a white or yellow-brown spot under the tip of a nail and can gradually thicken, discolor, and crumble it. It is most common in toenails and is stubborn: treatment takes months, and the infection often returns even when treatment works [1] [2].
Quick Answer: What is nail fungus?
Nail fungus is a common fungal infection that begins as a white or yellow-brown spot under the nail tip, then causes thickening, discoloration and crumbling, most often in toenails. Mild cases may need no treatment, while others use oral antifungals or medicated nail products. Results take at least four months to appear, and repeat infections are common. [1] [2]
What the research says
Terbinafine clearly beats placebo for toenail fungus. A Cochrane review of 48 studies (10,200 participants) found high-quality evidence that terbinafine was more effective than placebo for clinical cure (risk ratio 6.00, 95% CI 3.96-9.08; 8 studies, 1,006 participants) and moderate-quality evidence that it probably works better than azole drugs with a similar risk of side effects; evidence on recurrence was low quality (Kreijkamp-Kaspers et al., Cochrane Database Syst Rev, 2017 [3]).
Topical treatments work, but complete cure rates are relatively low. A Cochrane review of 56 studies (12,501 participants) found high-quality evidence that efinaconazole 10% solution beat vehicle for complete cure (risk ratio 3.54, 95% CI 2.24-5.60; 3 studies, 1,716 participants), while concluding that complete cure rates with topical treatments are relatively low (Foley et al., Cochrane Database Syst Rev, 2020 [4]).
Thinning the nail with urea may help medication work. A meta-analysis of six randomized trials and six non-randomized studies (424 participants given antifungals plus topical 40% urea) found that adding urea improved clinical cure compared with antifungals alone (odds ratio 2.05, 95% CI 1.03-4.11), but not mycological or total cure; the authors called for more rigorous trials (Kurniasari et al., Mycoses, 2025 [5]).
What Is Nail Fungus?
Nail fungus is a common infection of the nail, and its medical name is onychomycosis. It typically begins as a small white or yellow-brown spot under the tip of a fingernail or toenail. As the fungus grows deeper, the nail can change color, thicken, and crumble at the edge, and one infection can affect several nails [1].
When fungus infects the skin between your toes and the skin of your feet, the condition is called athlete's foot (tinea pedis). The two are closely linked: athlete's foot can spread to the nail, and a nail infection can spread to the foot. Nail fungus can affect fingernails, but it is more common in toenails [1].
One caveat shapes how to approach treatment: even when treatment is successful, nail fungus often comes back [1].
What are the signs of nail fungus?
Signs of nail fungus include a nail that becomes discolored, thickened or misshapen, and a provider should check it if self-care has not helped.
Symptom | What it looks like |
Thickened | The nail plate grows noticeably thicker than neighboring nails. |
Discolored | Yellow, brown, or white discoloration that spreads from the nail tip. |
Brittle, crumbly, or ragged | The nail edge or surface breaks apart easily. |
Misshapen | The nail loses its normal smooth contour. |
Separated from the nail bed | The nail lifts away from the skin underneath. |
Smelly | The infected nail gives off an unpleasant odor. |
When to See a Doctor
Mild nail fungus that is not bothering you may not need treatment, and sometimes self-care and nonprescription products clear it up. See a healthcare provider if self-care has not helped and the nail is becoming more discolored, thickened, or misshapen. Also talk with a provider if you have [1]:
Diabetes and think you are developing nail fungus
Bleeding around the nails
Swelling or pain around the nails
Difficulty walking
How does nail fungus start and spread?
Nail fungus is caused by various fungal organisms. The most common is a type called a dermatophyte. Yeast, bacteria, and molds can also cause nail infections, and the discoloration from a bacterial infection tends to be green or black [1].
What raises the risk of nail fungus?
Risk factor | Why it matters |
Older age | Increases the risk of nail fungus. |
Shoes that make your feet sweat heavily | Moisture creates an ideal environment for fungi. |
Past athlete's foot | The foot infection can spread to the nail. |
Walking barefoot in damp public areas | Swimming pools, gyms, and shower rooms are places where fungi thrive. |
Minor skin or nail injury | Small injuries give fungi a way in. |
A skin condition that affects the nails, such as psoriasis | Affected nails are more vulnerable to infection. |
Diabetes, blood flow problems, or a weakened immune system | These reduce the body's ability to handle the infection. |
Risk factors are listed in Mayo Clinic's overview of nail fungus [1].
What complications can nail fungus cause?
A severe case of nail fungus can be painful and may cause permanent damage to your nails. If your immune system is suppressed because of medication, diabetes, or another condition, a nail infection may also lead to other serious infections that spread beyond your feet [1]. People with conditions that cause poor blood flow to the feet should see a provider for foot care instead of managing thick nails on their own [2].
How is nail fungus diagnosed?
Your provider will examine your nails and may take nail clippings or scrape debris from under the nail. The samples go to a lab to identify the cause of your symptoms. This matters because other conditions, such as psoriasis, can mimic a fungal infection of the nail, and yeast and bacteria can also infect nails. Knowing the cause helps determine the best treatment [2].
Which nail fungus treatments actually work?
Treatment depends on the severity of the condition and the type of fungus. It can take months to see results, and even if your nail improves, repeat infections are common. Your provider may prescribe antifungal drugs that you take by mouth or apply to the nail [2].
Treatment | How it is used | Time to results | Key considerations |
Oral antifungal drugs (for example, itraconazole) | A daily pill for 6 to 12 weeks. | Four months or longer, until the new nail grows in. | Success rates appear lower in adults over 65. May cause rash and liver damage and can interact with other drugs, so occasional blood tests are needed. May not be recommended with liver disease, congestive heart failure, or certain medications. |
Medicated nail polish (ciclopirox) | Painted on infected nails and surrounding skin once a day. After 7 days, wipe the layers off with alcohol and start again. | Daily use may be needed for almost a year. | Slow, and it only works if applied consistently. |
Medicated nail cream or solution (for example, efinaconazole or tavaborole) | Rubbed into infected nails after soaking. | Months. | Works better if the nail is thinned first, with a urea lotion or by a provider filing the surface (debridement). May cause rash. |
Surgery | Temporary nail removal lets an antifungal reach the infection directly. Permanent removal takes the nail and its root. | Varies. | Permanent removal is the most effective but least used option. |
Mayo Clinic describes efinaconazole (Jublia) and tavaborole (Kerydin) as antifungal creams; the Cochrane review above studied them as nail solutions [2] [4].
Which home care and over-the-counter options help nail fungus?
Often you can take care of a fungal nail infection at home, especially a milder one [2].
Home care step | How to do it |
Try a nonprescription antifungal cream | Products such as terbinafine (Lamisil) are available. If you see white markings on the nail surface, file them off, soak your nails in water, dry them, and apply the medicated cream or lotion. Even if this clears your symptoms, the infection commonly returns. |
Trim and thin the nails | Reduces pain by relieving pressure on the nails, and lets an antifungal reach deeper layers. |
Soften thick nails first | Use a urea-containing cream before trimming or filing thick nails. |
Get foot care from a provider if you have poor blood flow | See a provider instead of managing thick nails yourself. |
Which alternative medicine for nail fungus has research behind it?
Some research suggests that the supplement biotin might help strengthen weak or brittle fingernails, and some research shows that tea tree oil has antifungal effects and is often used to treat nail fungus. Talk with your healthcare provider about whether either is right for you [2].
Which habits can help prevent nail fungus?
These habits can help prevent nail fungus, reinfection, and athlete's foot, which can lead to nail fungus [1].
Habit | Why it helps |
Keep nails clean and dry | Wash hands and feet regularly, dry well, apply antifungal foot powder, and moisturize your nails. |
Wash your hands after touching an infected nail | Helps keep the fungus from spreading. |
Keep nails trimmed and straight | Cut straight across, smooth edges with a file, and file down thickened areas. Long nails create more places for fungus to grow. |
Disinfect nail clippers after each use | Prevents reinfection from contaminated tools. |
Wear absorbent socks or change socks during the day | Reduces moisture. |
Choose shoes made of materials that breathe | Limits the dark, sweaty environment fungi like. |
Discard old shoes or treat them | Use disinfectants or antifungal powders. |
Wear footwear in pool areas and locker rooms | Avoids direct contact with surfaces where fungi thrive. |
Choose a salon that sterilizes its tools | Or disinfect the tools you use for home pedicures. |
Give up nail polish and artificial nails | Mayo Clinic lists this as a prevention step. |
Treat athlete's foot with an antifungal product | Stops the foot infection from reaching the nail. |
A nail hardener may also help strengthen nails and cuticles [1].
What is the bottom line on nail fungus treatment?
Nail fungus is common, often mild, and manageable, but it is stubborn. It grows out slowly, treatments take months, and reinfection is common. Start with the prevention habits above and, if the nail is becoming more discolored, thickened, or misshapen, consider a nonprescription antifungal. See a healthcare provider if the infection is painful, self-care is not working, or you have diabetes, circulation problems, or a weakened immune system. A simple lab test can confirm the cause and guide treatment [1] [2].
Frequently Asked Questions
What is nail fungus (onychomycosis)?
Nail fungus, medically called onychomycosis, is a common infection that begins as a white or yellow-brown spot under the tip of a fingernail or toenail. As it goes deeper, the nail may discolor, thicken, and crumble at the edge. It is more common in toenails than fingernails, and it can affect several nails.
Is nail fungus contagious?
The fungus can spread. Athlete's foot can spread to the nail and a nail infection can spread to the foot, and you can pick fungi up from places where they thrive, such as gym shower floors and dark, sweaty shoes. Disinfecting nail clippers and choosing a salon that sterilizes its tools helps lower the risk.
What causes nail fungus?
Various fungal organisms cause it, most commonly a type called a dermatophyte. Yeast, bacteria, and molds can also infect nails, and the discoloration from a bacterial infection tends to be green or black.
Can nail fungus go away on its own?
Treatment is not always needed for mild cases, and sometimes self-care and nonprescription products clear the infection. Even when the nail improves, the infection often comes back, so see a provider if self-care does not help and the nail becomes more discolored, thickened, or misshapen.
How long does nail fungus treatment take?
Expect months. Oral antifungals are usually taken daily for 6 to 12 weeks, but you will not see the end result until the nail grows back completely, which can take four months or longer. Medicated nail polish may be needed daily for almost a year.
What is the best treatment for nail fungus?
Oral antifungal drugs are often the first choice. Medicated nail polish, creams, and solutions are options for milder cases, and surgery to remove the nail is the most effective but least used option. The right choice depends on severity, the type of fungus, and your overall health.
Can I treat nail fungus at home without a prescription?
Often, yes. Nonprescription antifungal creams and ointments, such as terbinafine (Lamisil), are available. File off white surface markings, soak your nails, dry them, and apply the product. Trimming and thinning the nail helps reduce pain and lets the medication reach deeper layers.
Does tea tree oil work for nail fungus?
Some research shows tea tree oil has antifungal effects, and it is often used for nail fungus, but the evidence is limited. Talk with your healthcare provider before relying on it.
Why does nail fungus keep coming back?
Repeat infections are common even when treatment works. Fungi thrive in warm, damp places and in dark, sweaty shoes, and untreated athlete's foot can spread back to the nail. Keeping feet dry, wearing breathable shoes, disinfecting nail tools, and treating old shoes help prevent reinfection.
Who is at highest risk for nail fungus?
Older adults, people whose shoes make their feet sweat heavily, people who have had athlete's foot, and people who walk barefoot in damp public areas are at higher risk. Minor nail injuries, skin conditions such as psoriasis, diabetes, poor blood flow, and a weakened immune system also raise the risk.
Related Resources
Related reading on Rinnit:
External resources for deeper reading:
References
Mayo Clinic Staff. Nail fungus: Symptoms and causes. Mayo Clinic. May 15, 2024. https://www.mayoclinic.org/diseases-conditions/nail-fungus/symptoms-causes/syc-20353294
Mayo Clinic Staff. Nail fungus: Diagnosis and treatment. Mayo Clinic. May 15, 2024. https://www.mayoclinic.org/diseases-conditions/nail-fungus/diagnosis-treatment/drc-20353300
Kreijkamp-Kaspers S, Hawke K, Guo L, et al. Oral antifungal medication for toenail onychomycosis. Cochrane Database Syst Rev. 2017;7(7):CD010031. PMID 28707751. https://doi.org/10.1002/14651858.CD010031.pub2
Foley K, Gupta AK, Versteeg S, et al. Topical and device-based treatments for fungal infections of the toenails. Cochrane Database Syst Rev. 2020;1(1):CD012093. PMID 31978269. https://doi.org/10.1002/14651858.CD012093.pub2
Kurniasari FT, Ervianti E, Damayanti, et al. Efficacy and safety of 40% urea as an adjuvant to antifungals for onychomycosis: a systematic review and meta-analysis. Mycoses. 2025;68(8):e70097. PMID 40827600. https://doi.org/10.1111/myc.70097
Medical disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. The clinical information in this guide reflects source material last updated in May 2024.
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