It looks like I have fungus beneath my toenail, but how can I be sure? Does toenail fungus go away on its own?

Yellowing, brittle and unusual-looking toenails can be a sign that a fungal nail infection, called onychomycosis, has taken root.

Experts say these infections do not go away on their own and can easily spread from person to person without treatment.

“Fungus tends to be greedy,” said Dr Boni Elewski, chair of the department of dermatology at the University of Alabama at Birmingham.

If you pick it up from close contact with someone who is infected or by walking barefoot in a locker room, for instance, it can then crawl under your toenail and spread into the nail itself, she said.

Wearing moist, sweaty shoes can encourage the fungus to grow.

Toenail fungus affects an estimated one in 10 people worldwide, and becomes more common with age – afflicting more than half of those aged 70 and up.

People with diabetes or weakened immune systems are also susceptible, said Dr Shari Lipner, a dermatologist at Weill Cornell Medical Centre in New York City.

Is it really fungus?

Experts say the first step to getting your normal toenail back is confirming you have fungus in the first place. Some telltale signs include thickened, discoloured, cracked, misshapen and occasionally painful or smelly nails.

But fungus is to blame for only about half of abnormal-looking toenails, Dr Elewski said.

Toenail trauma, whether from one-time injuries or repetitive activity in too-tight shoes, can also cause discoloured or thick toenails. “Eyeballs alone are not enough to be sure it’s onychomycosis,” she said.

According to Dr Lipner, doctors usually confirm toenail fungus by examining a clipping under a microscope.

They can also perform a polymerase chain reaction test or a fungal culture to determine which fungus species has infected your nail.

But these tests are not always necessary because most people have a type of fungus called trichophyton rubrum, Dr Lipner said.

If your treatment is not working, however, your dermatologist may want to learn more about the organism living under your nail.

Prescription antifungals usually take care of the problem, but it is a bad idea to take them without confirming you have the fungus first, Dr Elewski said.

Unnecessary antifungal use can make these drugs less effective over time, contributing to a growing problem called antifungal resistance.

Which antifungals work best?

Although some drugstores devote entire aisles to over-the-counter fungus salves, Dr Elewski said the best a non-prescription treatment or home remedy can do is improve your nail appearance.

If you want to kill the fungus, a prescription antifungal is the only option, said Dr Antonella Tosti, a dermatologist who treats nail disorders at the University of Miami Miller School of Medicine.

There are topical prescriptions, including creams, ointments or serum-like solutions; and oral antifungals, meaning pills.

Topical antifungals can be useful for milder cases affecting just one or two toenails, Dr Lipner said.

But one downside is that you might have to apply the medication for about a year before the fungus is completely gone.

If there is fungus under multiple nails, or if the toenails are extra thick, Dr Lipner said, she usually opts for oral prescriptions.

These pills – terbinafine or itraconazole – can kill toenail fungus in about three months. Even after the oral pills kill off the fungus, Dr Lipner said your toenail may look funky for a year as the new, uninfected one grows in.

In the meantime, some drugstore remedies could improve nail appearance by soothing the surrounding skin or thinning the nail, Dr Elewski said.

It is also usually fine to use nail polish on your infected toenail while taking oral antifungals, Dr Lipner said. But do not do that if you are using topical medications.

Whether you are prescribed a topical or oral antifungal, Dr Tosti said it is important to stay on top of the treatment every day.

“This is not something you can cure in a few weeks,” she said. “Compliance is very important.”

How can I avoid repeat infections?

Successfully eliminating toenail fungus does not mean you cannot get it again, experts warn.

In fact, an estimated 25 per cent of people get repeat infections.

Dr Lipner recommended thoroughly washing any socks or other clothing that was in contact with your first infection. Discard the shoes you wore often when you had toenail fungus, or use disinfectant spray on those shoes, she added.

To stave off toenail fungus in general, keep your nails trimmed and avoid walking around barefoot in gym locker rooms or around swimming pools, Dr Lipner said.

If you perspire often in closed-toed shoes, wear moisture-wicking socks and change into dry shoes if you can.

If the skin on your foot becomes dry, itchy, flaky or inflamed, you might have athlete’s foot, which is caused by the same fungus that can spread to your toenail. So, it is important to get treated right away.

Unlike with toenail fungus, some over-the-counter medications can help with athlete’s foot.

“But don’t go blindly treating yourself,” Dr Lipner said. “You want to confirm with a dermatologist you’re treating the right thing.” NYTIMES