Introduction

Onychomycosis, the medical term for a fungal infection of the toenail. It is a condition that attacks the toenails and sometimes the fingernails.¹ Although dermatophytes (a type of fungal infection) are the main culprits, moulds and yeasts that are usually grouped as non-dermatophytes can also be to blame for fungal infections.¹ 

Over 50% of all nail conditions are caused by onychomycosis, which has an estimated 5.5% prevalence worldwide.³ The infection usually shows up as thick, discoloured, brittle nails, and in more advanced stages, it can cause pain or discomfort. It is not life-threatening, but because of its physical and psychological repercussions, it can impact quality of life. 

In people with other comorbidities such as diabetes or impaired circulation, untreated onychomycosis can result in increasing nail loss, discomfort, and secondary bacterial infections like cellulitis.^1,4 The condition may worsen if the illness spreads to nearby skin or neighbouring nails.⁵  

To avoid problems and enhance patient outcomes, early and efficient treatment is crucial. For mild to moderate cases of toenail fungus, topical antifungal therapies are essential. These therapies address the fungal infection locally by applying them directly to the afflicted nail and surrounding skin. 

Topical therapies are recommended for people who cannot tolerate systemic drugs because of possible adverse effects or contraindications, even though oral antifungals are frequently more effective for severe cases.⁶ Many patients now find topical formulations to be a helpful choice due to recent improvements in their efficacy.

Causes and risk factors of toenail fungus

Many different kinds of fungi can cause toenail fungus, but dermatophytes are the most frequent offenders. A class of fungi known as dermatophytes flourishes in keratin-rich habitats, including the skin, hair, and nails.⁵ 

The two main types that cause onychomycosis are Trichophyton rubrum and Trichophyton interdigitale.⁵ These fungi cause the typical symptoms of toenail fungus by invading the nail bed and plate. Other fungal species can potentially cause onychomycosis, in addition to dermatophytes, although they can sometimes affect toenails, including yeasts (especially Candida albicans) are more frequently linked to infections of the fingernails.^{1, 5} 

Some less common causes of toenail fungus from nondermatophytic moulds like Fusarium and Scopulariopsis are more common in tropical and subtropical areas where the climate is conducive to their growth.⁵ Geographical differences exist in the distribution of fungal species; for example, dermatophytes are predominant in temperate areas, whereas yeasts and moulds are more prevalent in warmer temperatures.⁵ 

Effective treatment of toenail fungus requires knowledge of the particular fungal species that causes it. Since various fungi may react differently to antifungal treatments, a precise diagnosis is crucial to the treatment of the condition.

A person's risk of toenail fungus is increased by a number of factors. These elements fall under three general categories: 

1. Lifestyle-associated
2. Environmental
3. Physiology

Lifestyle-associated risk factors

• Skin problems: Toenail fungus is more likely to develop in those who already have skin problems like psoriasis or athlete's foot¹⁴
• Smoking and Heavy Alcohol Use: Lifestyle choices that have been associated with a higher risk of onychomycosis include smoking and heavy alcohol use¹
• Genetic Predisposition: A genetic predisposition to fungal infections may exist in certain people¹⁵

Environmental risk factors

• Poor Foot Hygiene: People are more likely to come into contact with fungal spores during barefoot walking in public places like locker rooms, swimming pools, or showers.
• Sweaty Feet: Sweating can produce a damp atmosphere that encourages the growth of fungi. This issue is made worse by wearing socks or occlusive shoes made of non-breathable materials.
• Nail Trauma: Fungi can infiltrate through wounds to the nail or surrounding skin.¹

Factors associated with physiology

• Ageing: One of the biggest risk factors for onychomycosis is age. Because of slower nail growth, weakened immune systems, and decreased peripheral circulation, toenail fungus is more common as people age^{5, 8}
• Diabetes: Because diabetes affects circulation and the immune system, people with diabetes are more likely to develop toenail fungus. Patients with diabetes are also more vulnerable to consequences from infections that go untreated⁹
• Weakened Immune System: HIV/AIDS and chemotherapy are two conditions that impair immune function and make a person more susceptible to fungal infections¹⁰
• Poor Circulation: Toenail fungus can be predisposed to in those with peripheral vascular disease and other diseases that impact blood flow to the extremities¹¹

Both prevention and therapy depend on a thorough understanding of these causes and risk factors. People can lower their risk of this chronic condition by addressing modifiable risk factors, such as improving foot hygiene or avoiding extended exposure to dampness, and by getting treatment as soon as symptoms appear.

How do topical antifungal treatments work?

Topical antifungal medications either act as fungistatic (preventing fungal growth) or fungicidal (destroying fungi), by focusing on the fungal infection at the nail site.¹⁶ The main mechanism targets ergosterol, a crucial element specific to fungal cells, found in their cell membrane. The fungal cell membrane becomes unstable in the absence of ergosterol, which causes cellular contents to leak out and ultimately results in cell death.¹⁶

These substances are immediately administered to the afflicted nail and surrounding skin as lotions, gels, lacquers, or ointments. Drug penetration, however, can be difficult because of the thick keratin nature of nails.¹⁷ Certain formulations contain substances like thiols to improve drug administration and promote nail permeability.

For toenail fungus, oral antifungal medications are typically more successful than topical ones, particularly in more severe infections. Because oral medications like terbinafine and itraconazole work by delivering systemic antifungal activity into the bloodstream to deeper layers of the nail bed, they have greater cure rates.¹⁷ On the other hand, topical therapies are less helpful for advanced infections because of their limited capacity to completely permeate the nail plate.¹⁶ Due to their low systemic absorption, topical antifungals are far safer than oral treatments.^{18, 19}

Topical antifungal treatments for toenail fungus

People who want to treat mild symptoms of toenail fungus without a prescription can easily find a number of over-the-counter (OTC) topical antifungals. The synthetic antifungal drug tolnaftate works well against dermatophytes, which are the most prevalent fungi that cause nail infections.²⁰ It comes in a variety of forms, including creams, sprays, and powders, and functions by preventing the growth of fungi. Although it is commonly used to treat athlete's foot, its ability to effectively cure toenail fungus may be limited because of its poor nail penetration.²⁰

Another OTC option that inhibits fungal growth is undecylenic acid, which is generated from castor oil and breaks down fungal cell membranes.²⁰ 

A common antifungal is clotrimazole, which is sold as a cream or solution. Inhibiting the formation of ergosterol in fungal cell membranes, it works against a variety of fungi, including yeasts and dermatophytes. To get noticeable benefits for toenail fungus, long-term, continuous use is required.²⁰

Healthcare professionals may recommend stronger topical antifungals designed to pierce the nail plate and reach the infection site in cases of toenail fungus that are more severe or persistent. The triazole antifungal efinaconazole is applied directly to the nail as a solution. Targeting ergosterol synthesis, it prevents fungal development and has shown efficacy against moulds, yeasts, and dermatophytes.²¹ Mycological cure rates of up to 55% have been observed in clinical investigations with daily treatment for 48 weeks. It is a popular prescription alternative because of how simple it is to use.²¹

Tavaborole is an antifungal that inhibits leucyl-tRNA synthetase, hence disrupting fungal protein synthesis. It has shown effectiveness against certain moulds and dermatophytes.²²

Ciclopirox is an antifungal lacquer. When used regularly for 6–12 months, ciclopirox is still a cost-effective treatment for mild to moderate infections, despite being less effective than more recent medications like efinaconazole or tavaborole.²⁰

To cure toenail fungus, some people look for natural options, although there is not enough evidence that these work. The antifungal effects of tea tree oil have been shown to combat Trichophyton rubrum, a common source of toenail fungus.²³ Results vary and frequently call for a combination with conventional therapies, while some studies indicate that regular use over several months may minimise fungal development.²³

Vicks VapoRub, which contains eucalyptus oil, menthol, and camphor, has drawn interest as a possible home cure.²⁴ After 48 weeks of daily use, 55% of subjects in a small study claimed partial clearance. Its effectiveness is still mostly anecdotal, though, and it shouldn't be used in place of effective antifungal treatments.²⁴

Because vinegar soaks are acidic and may generate an environment that is not conducive to fungus growth, they have been proposed as a natural remedy.²⁵ There isn't any solid clinical proof that vinegar soaks can treat toenail fungus, but they might assist with symptoms like brittleness or discolouration.²⁵

To treat toenail fungus, topical antifungal medicines come in a variety of forms, from over-the-counter drugs like tolnaftate and clotrimazole to prescription-strength medications like efinaconazole and tavaborole. Because nails grow slowly, these treatments are generally safe and well-tolerated, but their success depends on regular use over long periods of time.

Preventive measures and lifestyle changes

Preventing fungal infections requires keeping feet dry and clean. Sweaty feet make an excellent breeding ground for fungi, which prefer warm, humid conditions.²⁶ Daily foot washing with antibacterial soap and thorough drying, with special attention to the areas between toes, is crucial to preventing this. 

By using foot powder, you can further lower the chance of fungal growth by absorbing extra moisture.²⁶ Maintaining a healthy foot environment requires wearing moisture-wicking socks and breathable shoes. Natural shoe materials, such as leather, let feet "breathe," which prevents moisture buildup.²⁷ It's best to switch up your shoe rotation and let each pair air dry for at least 24 hours in between wears. Because synthetic fibres are better at drawing perspiration away from the skin, moisture-wicking socks are better than those made of cotton or wool.²⁷

Another important preventive step is to avoid going barefoot in public places. Fungal infections are frequently found in public areas like gym showers, locker rooms, and swimming pools. To keep your feet away from potentially contaminated surfaces, always wear sandals or flip-flops in these areas.²⁸ This little practice can drastically lower the chance of coming into contact with fungus and other infections.

Preventing fungal infections requires regular nail care and good hygiene habits. To keep debris from building up beneath your nails, keep them short and clipped straight across. Before using nail clippers, scissors, and other pedicure equipment, it is essential to sterilise them, ideally with rubbing alcohol.²⁹ To stop diseases from spreading, don't share these tools with other people. The risk of toenail fungus can be significantly decreased by making certain lifestyle adjustments in addition to these precautions. To make your shoes unwelcoming to fungi, sprinkle them with antifungal powder.³⁰

Conclusion

Topical antifungal medications function by either blocking protein synthesis or rupturing fungal cell membranes, which targets fungal growth at the infection site. Prescription medications like efinaconazole and tavaborole provide greater effectiveness for more difficult infections, while over-the-counter alternatives like clotrimazole and undecylenic acid are available for milder infections. 

Preventive steps are crucial to lowering the risk of infection or recurrence. These include keeping feet dry and clean, wearing breathable shoes, avoiding barefoot walking in public places, and practising good nail cleanliness. Oral antifungals or more sophisticated treatments like laser therapy can be required for more severe instances.

Although topical therapies or home remedies can manage many cases of toenail fungus, serious or chronic infections should be treated by a physician. Significant nail discolouration, thickness, pain, or an unpleasant odour are among the symptoms that could point to an advanced infection that needs medical attention. To avoid complications, people with weakened immune systems or underlying medical disorders, such as diabetes, should see a podiatrist as soon as they notice an infection. 

A medical professional can use laboratory testing to confirm the diagnosis and suggest a treatment plan that is appropriate for the severity of the problem.