Introduction

Did you know that fungal toenail infection (Onychomycosis) is the most common nail infection in the general population? They often start small with nail discolouration but can quickly become thickened, and sometimes very painful. 

Fungal toenail infection is a common fungal infection that affects about 12 -13% of the population. Its prevalence is higher in people with poor immunity than in those who are healthy. 

It is caused mainly (80 -90% of the time) by dermatophyte fungi of the Trichophyton rubrum and Trichophyton mentagrophytes species. However, non-dermatophytes, like yeasts and moulds, can also result in fungal nail infections in about 2 - 40% of cases.^1,2

These fungi usually thrive in warm and damp environments like: 

• Non-breathable stocks
• Sweaty shoes
• Public showers

Although many fungi species cause toenail infections, identifying the specific type for an individual case is crucial for choosing the most effective treatment. 

This article breaks down the common fungal species that cause fungal toenail infection, how they spread,  how to prevent them, and how to treat them.

Types of fungi causing toenail infections

The three major types of fungi responsible for toenail infections are:³

Dermatophytes

These are the most common causes of toenail infections, as they constitute 80 -90% of the cases. The main species are:

• Trichophyton rubrum (most common)
• Trichophyton mentagrophytes
• Epidermophyton floccosum

Yeasts (candida species)

Yeast infections are the most common cause of infection in people with weak immunity or frequent exposure to water. The most important species in this group include:

• Candida albicans
• Candida parapsilosis

These fungi are normally present in the  skin without causing issues, but can cause infection in people with a weakened immune system.

Non-dermatophyte moulds

These are opportunistic infections and are less common. However, they still cause infections, especially in people with nail injury, people in warmer climates, and the elderly.^{3, 4} The major species in this group are:

• Scopulariopsis brevicaulis
• Aspergillus species
• Fusarium species

The elderly are more prone to nail injuries due to a higher incidence of nerve and peripheral blood vessel disease, which predisposes them to non-dermatophyte fungi infection.

What are the risk factors for fungal toenail infections?

Toenail infection risk is greater in people who:^{2, 3}

• Have poor foot hygiene
• Are of advanced age 
• Walk barefoot in pools and locker rooms
• Smoke
• Are Assigned Male at Birth (AMAB) (males are up to 3 times more likely to have fungal toenail infections than females)
• Wear shoes that are tight and non-breathable 
• Have trauma or injury to the nail
• Have weak immunity, e.g. diabetes, human immunodeficiency virus (HIV), failure/transplant of organs

Symptoms of toenail fungal infections

• Nail discolouration (yellow, white, or brown)
• Thickened or brittle nails
• Nail detachment or deformity
• Foul odour in severe cases

Diagnosis

For appropriate treatment, diagnosis of fungal toenail infection, or onychomycosis, should be accurate. Inappropriate diagnosis results in the wrong treatment regimes, prolonged discomfort, and possibly complications. Diagnosis involves:

• Clinical examination
• Laboratory tests

A part of the infected nail is stained with KOH (potassium hydroxide) and examined under a microscope. Thereafter, organisms are allowed to grow on the sample to identify the specific fungus causing the infection is a gold standard technique for diagnosis.⁴

Treatment of toenail fungal infection

As a result of contamination of other nails in the same patient or family member, infection relapse is possible, which makes the toenail infection treatment challenging.

Toenail fungal infection can be treated using surgical or chemical removal of the infected nail, debridement, oral antifungal drugs, topical antifungal drugs, or a combination of all of these.¹ 

Moreover, with the introduction of oral antifungal drugs such as terbinafine and itraconazole, the treatment of fungal toenail infection has greatly improved.

However, toenail infections that are caused by non-dermatophyte organisms, such as Fusarium, are very hard to treat.³

The  treatments commonly used for fungal toenail infection are:^{1, 3, 4} 

Topical antifungal treatments (e.g., creams)

Topical antifungal treatments don’t always work because the keratin protein surface found on toenails reduces drug penetration.

Clinical cure rates of about 2-40% of clinical cure rates have been observed with topical antifungals. It has also been noted that some topical antifungals attach to the nail bed instead of penetrating deeper to the site of infection.

However, it's still being used in people like the elderly and those with low immunity, who cannot tolerate oral antifungal drugs because of their high tendency to develop liver damage as a result.

Oral antifungal medications (e.g., terbinafine, itraconazole, fluconazole)

Oral antifungal drugs taken by mouth are the go-to for the treatment of fungal toenail infections. These, especially the three mentioned above, are all effective, with a clinical cure rate ranging from 40 to 80%.

Other treatments

Laser therapy for cosmetic treatment or nail removal in very severe cases of fungal toenail infections can also be done.³

Why do fungal toenail infections recur?

Various factors are responsible for infection recurrence and include:³

• Genetic predisposition coupled with low immunity increases susceptibility to the recurrence of fungal infection of the toenail. In this case, infection is difficult to cure permanently
• Failure to eradicate the fungus causing infection or reinfection by a completely new strain
• Some strains of the fungus, which have a thick covering, allow them to develop resistance to antifungal agents

How can you prevent fungal toenail infection?

• Ensure you keep your feet clean and dry
• Wear breathable shoes, and remember to change your socks regularly
• Avoid walking barefoot in public areas
• Trimming your nails properly and avoiding any form of injury to your nails
• In individuals prone to infection, antifungal powders or sprays can be used

Summary

Fungal toenail infection, though sometimes seen as a mainly cosmetic problem, can be very stubborn and uncomfortable if not treated. The elderly, people with low immunity, like those with HIV or diabetes, have a higher tendency to develop fungal toenail infections, especially those caused by yeast and moulds.

Reduction in blood circulation to the periphery from peripheral blood vessel disease also further increases their risk of infection.

To be able to prevent and treat fungal toenail infection properly, a good understanding of the common causes of fungal toenail infections, e.g, dermatophytes like Trichophyton rubrum, yeasts like Candida, and moulds like Fusarium, is needed.

The good news is that with a few simple habits like:

• Keeping your feet clean and dry
• Wearing breathable shoes
• Properly trimming nails

You can be protected from fungal toenail infection.

If you notice an infection, seek healthcare advice so that you can begin treatment as soon as possible.

Frequently asked questions (FAQs)

Q1 - How do I know it is a toenail fungal infection I have and not just a damaged nail?

Answer - Fungal infections will usually be thickened, yellow, white, or brown, very brittle, and sometimes foul-smelling. If just one nail is damaged following injury, despite the discolouration, it will usually grow out normally over time. A KOH test can be done to confirm if it's a fungal infection.

Q2 - Can toenail fungus infection go away without treatment?

Answer - No, you will need to get it treated, otherwise it will worsen with time, and is capable of spreading to other nails or even your skin. 

Q3 - How can I prevent toenail fungal infections?

Answer - You can prevent toenail fungal infections by ensuring that your feet are clean and dry, avoiding walking barefoot in locker rooms, wearing breathable shoes, and trimming your nails properly.

Q4 - Is toenail fungal infection easy to clear out?

Answer - Topical treatments with consistent use help symptoms after several months of proper use. The duration of the treatment differ depending on the severity of the infection.

However, oral antifungal medicine typically takes between 6 and 12 weeks to work, and up to 6-12 months to see visible nail improvement since toenails grow out slowly.

Q5 - Can toenail fungal infection spread from one person to another?

Answer - Yes, it can spread from one person to another if they share socks, nail clippers, shoes, pools, and locker rooms. It can also spread to other nails on the same individual if not treated.

Q6 - Is toenail fungal infection painful?

Answer - At the early stages, it is painless. But later in its course, it may become painful.