Overview

Toenail fungus, also known as onychomycosis, is a common fungal infection of nails. This infection affects both fingernails and toenails, but it is more common in toenails. The condition is caused by a fungus called dermatophytes (Tinea unguium). Dermatophytes are the main cause of 90% of toenail fungal infections. When fungus infects the toenail, it becomes thick and yellow, with white spots or streaks. As infection deepens, the nail may discolour and crumble at the edge. Toenail fungus is widespread among older adults, affecting 1 in 10 individuals overall. This number rises to 1 in 2 (50%) for individuals over 70.^1,2,3 Identifying the risk factors leading to toenail fungal infections helps in proper management and decreases the chance of individuals developing an infection, which is difficult to treat if left untreated.

What are the common risk factors for developing toenail fungus?

Risk factors for developing toenail fungus include:

Environmental factors

Poor foot hygiene

• Not washing feet thoroughly with soap and water
• Not drying feet properly after washing or bathing
• Not changing socks frequently or wearing sweaty socks for extended periods^1,2,3

Wearing improper footwear

• Wearing tight-fitting shoes that compress the toes
• Wearing non-breathable shoes that limit proper air circulation^1,2,3

Exposure to damp environments

• Walking barefoot in damp or moist public places such as gyms, communal showers, and pools increases the exposure to fungal spores, as these environments are ideal for fungal growth^1,2,3

Medical conditions

Individuals with underlying medical conditions are more susceptible to toenail fungus because of their weakened immunity or poor circulation. The medical conditions include:

Diabetes

Individuals with diabetes have high glucose serum levels, vascular diseases, and reduced foot sensation, making them susceptible to toenail fungus.⁴ One-third of individuals with diabetes usually develop toenail fungus, which can lead to serious conditions if left untreated.⁵

HIV/AIDS

Individuals with HIV, particularly those with low CD4+ T-cell counts (typically below 400 cells/mm³),  are at increased risk of toenail infection because of their weak immune system.⁶ Every 1 in 4 people with HIV develop toenail fungus.⁵

Autoimmune disorders

Autoimmune diseases like lupus and scleroderma weaken the immune system and make it more difficult for the body to fight against infections. These diseases can either affect the nails directly or favour the environment for fungal growth.⁷

Peripheral artery disease

People with peripheral artery disease who have poor blood circulation delay healing from minor cuts or cracks, making them more prone to bacterial or fungal infections. Some studies also found that toenail infection is a warning sign or a potential indicator of peripheral arterial disease.⁵

Ageing-related circulation decline

Advancing age can bring changes in the morphology and growth of the nail plate. The mechanism underlying these changes is still not fully understood. However, it is assumed that they result from poor blood circulation to the distal extremities or due to the effects of ultraviolet radiation. The normal growth rates of fingernails and toenails were 3.0 and 1.0 mm per month, respectively. This rate tends to decrease by approximately 0.5% per year after age 25.⁸

Trauma or injury

Trauma or injury to the nails, such as accidental clipping or repetitive impact from activities like running or sports, results in minor cuts or cracks. These openings can act as portals for entering fungus.⁹

Cosmetic factors

Frequent use of nail polish or acrylic nails

• Nail polish traps moisture from the nail bed, and creates an environment that promotes fungal growth
• Acrylic nails, if applied improperly or worn too long, trap moisture and prevent nails from breathing, leading to fungal overgrowth¹⁰ 
• One study found that 67 out of 68 women who wore artificial nails with a nail concern developed fungal infections after removal¹¹ 
• A recent study found that when nail polish top coat comes into contact with the fungus, it can pick up the fungus and spread to other nails or even to other people if they use the same tools on their nails¹²

Genetic predisposition

Family history of fungal infections 

Toenail fungal infection is not passed down from parents to children. However, an individual's susceptibility to acquiring an infection can be inherited from parents or siblings.¹³ 

Prolonged use of antibiotics

Prolonged use of antibiotics weakens the immune system to fight against fungi, leading overgrowth of fungi. This is because antibiotics can disrupt the natural balance of bacteria in the gut and negatively impact the immune response.¹⁴

Other factors

Other factors that can develop toenail fungus are:

• History of hepatitis
• Patients with a travel history of places where hepatitis is widespread
• Alcohol consumption
• Hobbies in the past can cause disease recurrence or the development of new infections
• Certain conditions like hand fungus (Tinea manuum), jock itch (Tinea cruris), or psoriasis² 

What are the basic prevention strategies?

• Practice good foot hygiene
• Wear breathable footwear or moisture-absorbing socks
• Avoid walking barefoot in public areas
• Keep nails trimmed and clean
• Boost immune health through diet and exercise
• Use antifungal sprays or powders when necessary^1,2,3

FAQ’s

Can I wear socks to bed with toenail fungus?

Yes, but wear clean and breathable socks to bed if you have toenail fungus. This helps to prevent the spread of the fungus to other areas. Avoid wearing dark socks as they trap heat and moisture, and create a dark environment, promoting fungal growth.

Do I need to throw away my shoes if I have toenail fungus?

Yes, you should throw away the shoes you wore before treating toenail fungus. The fungus can live in shoes and spread easily, and can be reinfected by wearing shoes that have been infected. Fungal spores can stay dormant for months in shoes, so you can spread the infection to others.

What worsens toenail fungus?

Toenail fungus worsens when your feet are damp, moist, or sweaty or wear tight-fitting shoes. Other factors that can worsen the infection include sharing items (shoes, towels, or nail clippers), nail injuries, athlete's foot, diabetes, improper acrylic nail application, and using nail polish on the infection.

Can I put nail polish on toenails with fungus?

It is not recommended to put nail polish on toenails infected with fungus until the infection is completely cleared. Nail polish can trap moisture and create an environment that promotes fungal growth and potentially worsens the infection.

Can toenail fungus spread to other areas of your body?

Yes, toenail fungus spreads to other parts such as other toenails, skin between the toes (athlete’s foot), groin area (jock itch), or scalp.

Summary

Toenail fungus is a common fungal infection of nails, mostly seen in older adults. Individuals with diabetes, peripheral artery disease, and HIV/AIDS are at increased risk because of poor circulation and weakened immune systems. People who work in damp or moist environments, wear tight-fitting shoes, or maintain poor hygiene are also more susceptible. A positive family history of toenail fungus can also increase an individual’s risk. Hence, maintaining proper foot and nail hygiene, wearing clean, breathable shoes and socks, and addressing underlying medical conditions protects overall foot health. Individuals should be aware of the signs and symptoms of the infection and immediately consult a doctor or a podiatrist for diagnosis and treatment. Also, it is important to be patient and follow the doctor's instructions carefully as treatment of toenail fungus may take several months or years to heal completely. Further research is necessary to understand the underlying mechanisms and develop more effective prevention and treatment strategies.