What Causes Toenail Fungus? Risk Factors & Prevention

Quick answer:Toenail fungus is caused by dermatophyte fungi — and sometimes yeasts or molds — that enter through tiny cracks and thrive in warm, damp shoes. Risk rises with age, athlete’s foot, nail injury, diabetes, and sweaty feet. A podiatrist can confirm it and treat it effectively. Call (810) 206-1402.

Understanding what causes toenail fungus is the first step toward actually getting rid of it — and more importantly, preventing it from coming back. In our clinic, we see patients who’ve cleared an infection only to get re-infected within months because they never addressed the source. The fungus is almost always coming from somewhere specific in their environment or routine.

The Main Cause of Toenail Fungus

Toenail fungus is caused by microscopic fungi that invade the nail plate or nail bed. The most common culprit — responsible for about 90% of cases — is Trichophyton rubrum, a dermatophyte (a type of fungi that feeds on keratin, the protein that makes up nails and skin). Less commonly, toenail fungus is caused by other dermatophytes (T. interdigitale), non-dermatophyte molds (like Fusarium and Aspergillus), or yeasts (Candida).

These organisms are everywhere in our environment — soil, surfaces, and the skin of other people. The question isn’t whether you’re exposed; it’s whether the fungus can get a foothold. That depends on your nail health, immune system, and environment.

https://www.youtube.com/watch?v=qK7K4ZVUEM4

How Does Toenail Fungus Enter the Nail?

Fungi can’t penetrate healthy, intact nail tissue from above. They need a portal of entry — usually one of the following:

• The distal (free) edge of the nail — the most common entry point; the gap between the nail edge and the nail bed allows fungal spores to penetrate and work their way up
• Trauma to the nail — even minor trauma (stubbing a toe, tight shoes that press on the nail) creates microscopic separations in the nail-bed junction
• Onycholysis — if the nail is lifting away from the nail bed for any reason, that gap becomes a direct fungal highway
• Adjacent skin infections — athlete’s foot (tinea pedis) spreads to the nail plate from infected surrounding skin, particularly around the lateral nail folds

Who Is Most at Risk?

While anyone can develop toenail fungus, certain factors dramatically increase susceptibility:

• Age: people over 60 have 3–4x higher rates; nails grow slower, thicken naturally, and circulation decreases with age
• Diabetes: impaired immune response and circulation make the feet highly vulnerable to fungal infection
• Poor circulation (peripheral arterial disease): reduced blood flow diminishes the immune defense delivered to the nail
• Weakened immune system: HIV, immunosuppressive medications (post-transplant, chemotherapy), or autoimmune conditions
• Previous nail trauma: even minor injuries create entry points for fungi
• Athlete’s foot history: tinea pedis almost always precedes or accompanies nail infection — the skin and nail share the same organism
• Sweaty feet (hyperhidrosis): warm, moist conditions accelerate fungal growth
• Narrow toe box footwear: high heels or pointed shoes crowd toes, creating micro-trauma and limited air circulation
• Family history: genetic susceptibility to fungal infections is well-documented

Where Do People Pick Up Toenail Fungus?

Specific environments where fungal transmission is most common:

• Swimming pools and pool decks — wet surfaces, barefoot traffic, and warm temperatures create ideal fungal breeding grounds
• Gym locker rooms and showers — high-traffic wet areas; fungal spores survive on surfaces for extended periods
• Nail salons — improperly sterilized tools (nail clippers, files, drill bits) can transfer fungi between clients
• Public showers at hotels, gyms, spas — even brief barefoot exposure on contaminated surfaces can trigger infection
• Shared footwear — borrowing someone’s shoes, socks, or even trying on shoes at a store without socks
• Within your own household — the bathtub or shower floor is one of the most common sources of self-reinfection and family transmission

Does Nail Polish Cause Toenail Fungus?

Dark or opaque nail polish doesn’t cause fungus on its own, but it creates conditions that support fungal growth: it blocks light, traps moisture under the nail, and prevents you from monitoring nail changes early. Keeping nails polished continuously without breaks is a known risk factor for nail fungus development and recurrence after treatment. If you wear nail polish, we recommend periods of 2–4 weeks with bare nails, and always use a clean base coat.

Preventing Toenail Fungus

• Always wear sandals or water shoes in public wet areas — pools, locker rooms, hotel showers
• Keep nails short and trimmed straight across
• Change socks daily; choose moisture-wicking materials over cotton
• Rotate shoes to allow complete drying between wears
• Disinfect nail clippers with 70% isopropyl alcohol before use
• Treat athlete’s foot promptly — don’t let skin infections reach the nail
• Apply antifungal spray to the inside of shoes regularly
• Choose salons that sterilize instruments in an autoclave or use single-use tools
• If you have diabetes, have a podiatrist examine your nails at every visit

Frequently Asked Questions

Can toenail fungus spread to other nails?

Yes — without treatment, toenail fungus spreads to adjacent nails by direct contact and through contaminated footwear and socks. The mechanism is the same as original infection: the organism spreads from infected nail or skin to an adjacent nail’s entry points. Treating early minimizes spread.

Is toenail fungus caused by poor hygiene?

Poor hygiene is one contributing factor, but it’s not the primary cause. Many people with excellent hygiene develop nail fungus simply from brief barefoot exposure in a high-risk area. Immune status, nail health, and genetics are more important determinants than hygiene alone.

Can you get toenail fungus from shoes?

Yes — fungal organisms survive in the warm, dark interior of shoes. If you’ve been treated for nail fungus but continue wearing the same shoes without disinfecting them, re-infection is common. Treat shoes with antifungal spray or UV shoe sanitizers, and discard very old footwear if infection keeps recurring.

Sources

• Gupta AK, Nakrieko SA. Onychomycosis infections: do laboratory results predict clinical response in patients. J Am Podiatr Med Assoc. 2015.
• Sigurgeirsson B, Baran R. The prevalence of onychomycosis in the global population. J Eur Acad Dermatol Venereol. 2014.
• Ghannoum MA, Hajjeh RA. Overview of fungal infections. Clin Infect Dis. 2000.
• American Academy of Dermatology. Nail fungus: who gets and causes. aad.org. 2025.

What is Toenail fungus?

Toenail fungus is a common foot/ankle condition that affects mobility and quality of life. Understanding the underlying cause is the first step in successful treatment. Our podiatrists at Balance Foot & Ankle perform a hands-on biomechanical exam, review your activity history, and use diagnostic imaging when appropriate to identify the root cause—not just treat the symptom. Many patients have been told to “rest and ice” without a deeper diagnostic workup; our approach is different.

Symptoms and warning signs

Common signs of toenail fungus include pain that worsens with activity, morning stiffness, swelling, tenderness when palpated, and difficulty bearing weight. If you experience sudden severe pain, inability to walk, visible deformity, numbness or color change, contact our office the same day or visit urgent care—these can signal a more serious injury such as a fracture, tendon rupture, or vascular compromise. Diabetics with any foot wound should seek same-day care.

Conservative treatment options

Most cases of toenail fungus respond to non-surgical care: structured rest, supportive footwear changes, custom orthotics, targeted stretching and strengthening protocols, anti-inflammatory medications when medically appropriate, and in-office procedures such as ultrasound-guided injections. We also offer advanced therapies including MLS laser therapy, EPAT/shockwave, regenerative injections, and image-guided procedures. Treatment is sequenced from least invasive to most invasive, and we explain the rationale at every step.

When is surgery considered?

Surgery is reserved for cases that fail 3-6 months of well-structured conservative care, when there is structural pathology (severe deformity, complete tear, advanced arthritis), or when imaging shows damage that will not heal without intervention. Our surgeons have performed 3,000+ foot and ankle procedures and prioritize minimally-invasive techniques whenever appropriate. We discuss recovery timelines, return-to-activity milestones, and realistic outcome expectations before any procedure is scheduled.

Recovery timeline and prevention

Recovery from toenail fungus varies based on severity and chosen treatment path. Conservative cases often improve within 4-8 weeks with consistent adherence to the protocol. Post-procedural recovery may range from a few days (in-office procedures) to several months (reconstructive surgery). Long-term prevention involves footwear assessment, activity modification, structured strengthening, and regular check-ins with your podiatrist if you have a history of recurrence. We provide written home-exercise plans and digital follow-up support.

In-Office Treatment at Balance Foot & Ankle

If home treatment isn’t providing relief for your toenail issues, our podiatry team at Balance Foot & Ankle can help with same-day evaluations and advanced in-office care.