Onychomycosis, or more plainly known as toenail fungus, is a fungal infection affecting the nails. This infection typically affects the toenails much more than the fingernails however symptoms in both areas are similar. In this article, we will explore the fungus causing this infection and the different potential causes of toenail onychomycosis. 

What fungus causes Onychomycosis?

The fungi that cause diseases of the skin, nails and hair are called dermatophytes. Dermatophytes need keratin to grow and keratin is a key protein used to make our skin, nails and hair. 

The dermatophyte species T. rubrum has been known to cause onychomycosis but other fungal species such as T. mentagrophyte and E. flocussum have also been known to cause onychomycosis.¹ 

These fungi have hyphae - long, thin filaments that are able to infiltrate our nails. In the same way, a tree establishes roots, dermatophytes are able to invade our skin, nails or hair by forming a network of hyphae. From this, the hyphae hub can release keratinases which are enzymes that are able to break down and digest keratin. This provides food and energy for the fungi to continue to grow.

Dermatophytes are responsible for 90% of onychomycosis cases.² When this happens, onychomycosis can also be named tinea unguium. Other fungi that cause onychomycosis are yeasts and saprophytic moulds that feed on dead skin cells.

Around 5.5% of the population have onychomycosis and incidence of toenail fungal infections are expected to increase in the future due to ageing population, changing climate and changes in footwear styles.³

What are the signs and causes of onychomycosis?

Common signs of onychomycosis

One, multiple or all toenails can look different if infected with toenail onychomycosis. Common signs that you may have toenail onychomycosis include:

• Colour changes: the toenail can become discoloured, usually appear yellow or brown in areas or the nail can have white spots within it
• Broken nail: the nail can become cracked and split and may even separate from the nail bed
• Uneven nail: the toenail can become uneven at the surface with some areas being thicker than others and overall be misshapen

Other than physical signs, there are no indicators of onychomycosis. It is not a painful infection but only a proper diagnostic test can confirm the abnormal toenails are due to a fungal infection and not a different cause.

How can I get toenail onychomycosis?

Dermatophytes, as with most fungal species, like to live in warm, moist and dark environments. The fungi are contagious and can spread quite easily therefore walking barefoot in public areas can increase your chance of getting toenail onychomycosis. Common areas that you could get exposed to the fungus may be:

• Gym showers: the water and warmth of a shower is a perfect environment for the fungi to live. If barefoot in the showers, it is likely that a fungus may have made contact with your skin or nail and can begin its invasion. To prevent this from happening, it's recommended to wear a flip-flop in the shower to provide a barrier between your foot and the floor
• Swimming pools: similar to a gym shower, the water temperature in a pool creates good conditions for dermatophytes to live. Wearing flip-flops is recommended to reduce the chance of becoming infected. Taking care to keep the toes dry after a swim session and before putting on shoes is good practice too
• Hotel floors: although the hotel may appear clean, fungi are microscopic organisms and there is no way of telling if fungi do exist in the area. In particular, carpets and rugs are good materials for retaining moisture so could become habitable environments for dermatophytes like T. rubrum 

Risk factors for onychomycosis

Walking barefoot in public areas such as those listed above can increase your risk of exposure to toenail onychomycosis. However, there are a variety of inherent risk factors, unrelated to the environment that some individuals may have that can increase their chance of having a toenail fungus. These can include:

Hyperhidrosis

Hyperhidrosis is a condition where an individual sweats excessively, even outside of exercise or physical activity. Whilst the armpits and chest are common areas that we might consider to sweat, surprisingly, it is our hands and feet that contain the most sweat glands in our body. Therefore, the excess sweat at the feet combined with wearing socks or shoes for the majority of the day can increase an individual's risk of getting onychomycosis as the warm, dark and moist environment encourages the fungi to grow. Keeping on top of foot hygiene, rotating shoes and wearing clean socks each day can help reduce the risk of getting a toenail fungus.

Diabetes

Diabetes is a condition impacting the body’s ability to control blood sugar levels. This excess sugar remains in the blood and this can affect a range of cells, tissues and organs in the body including the feet. Directly, this excess sugar can be removed by our sweat. However, this sugar can provide food to organisms like dermatophytes and encourage them to grow. Also, the excess sugar in the blood can alter and weaken our immune system. As a result, this makes it harder for individuals with diabetes to fight infections, making it more likely that an infection such as onychomycosis is able to persist. Keeping the feet dry and clean and attending appointments with a diabetic podiatrist (foot doctor) can help minimise the risk of getting onychomycosis. 

Age

As we age, our ability to heal wounds and fight infections slows down. This can mean that any cuts on the feet remain open for longer, providing more opportunities for dermatophytes to invade and establish hyphae. Our mobility may also decrease, making it harder to keep on top of good foot hygiene, increasing the risk of getting onychomycosis.

Poor blood circulation

diseases such as diabetes and peripheral artery disease as well as activities such as smoking can reduce blood circulation in the body. This means that there is less blood flowing towards the periphery areas of the body such as our fingers and toes. As there is reduced blood flow to the feet, less immune cells are able to readily defend against invaders such as dermatophytes, increasing one's risk of getting onychomycosis. 

Summary

Onychomycosis causes abnormalities in the toenails due to a fungal infection. The fungus is able to invade our nails and survives by releasing enzymes that break down keratin, a key component of our nails. A fungal infection in the feet leads to symptoms of broken, split and abnormal nail colours but overall is a painless infection. The fungi that cause onychomycosis are known as dermatophytes which specifically target the skin, nails and hair. These dermatophytes thrive in warm, moist and dark conditions. Certain lifestyle activities in public can increase one's chance of exposure to onychomycosis. In addition, there are a range of risk factors for onychomycosis. Keeping good foot hygiene and avoiding walking barefoot in public can help reduce the chance of getting onychomycosis.