Nail Fungus or Just Yellow? Check These 5 Things Before You Go to the Nail Salon

By Nanny Nails, nail salon in Nakhon Phanom | Updated 28 Sept 2026

The night before your pedicure, you take off your old polish and notice that one big toenail is cloudy yellow, a little thicker than the other, with a slightly crumbly tip. The first question that pops up: is this fungus, or just yellow from polish? And will the salon do my nails tomorrow? This article gives you 5 things you can check yourself in five minutes, so you know whether to keep your appointment or see a doctor first.

Let us say this up front. These 5 checks do not tell you whether you have fungus, because even doctors usually need to test a sample of the nail to know for sure. What they tell you is whether a doctor should see your nail first. For someone about to go to a nail salon, that is the more important question.

Why looking is not enough

Here is something most people do not know. Approximately half of nails with suspected fungus do not have a fungal infection. Nail psoriasis or a nail injury can look very much like fungus, which is why doctors often clip the nail, scrape its surface or collect debris from under it to look at under a microscope before choosing a treatment.

What does that mean for you? Neither you nor a nail technician can be certain just by looking. If someone at a salon says it is definitely fungus, or that it is not fungus so they can paint over it, both claims go further than the eye can tell. What anyone can do is notice the signs, then pass the question to someone who can test it.

How nail fungus happens

Fungi love warm, moist places. They get in through tiny openings in or around the nail and slowly spread. Nail fungus is more common in toenails than fingernails, because fungi thrive inside dark, sweaty, moist shoes.

What raises the risk:

• Age It affects roughly half of people over 70.
• Sweaty feet or hands and tight closed shoes all day.
• Athlete's foot (fungus on the skin of the foot, especially between the toes) or psoriasis.
• Diabetes poor circulation, or obesity.
• A past nail injury
• Walking barefoot in damp shared places such as communal showers and pool decks.
• Sharing towels, shoes or nail clippers
• Family members with nail fungus

Nail fungus also spreads from one person to another and from one nail to another. That is why a nail salon has to be especially careful.

5 things to check before your nail appointment

Take off all old polish, wash and dry your feet, then sit somewhere bright and go through the list one by one. The diagram shows where each check is.

Check 1: colour change, and where it starts

The first sign people usually notice is a change of colour on part of the nail. Yellow, brown and white are common, but it can also be orange, greenish black or black. Where it starts helps: the colour change usually begins at the tip of the nail and spreads towards the cuticle, often starting as a white or yellow-brown spot under the tip.

Compare that with a polish stain, which is usually an even yellow across the whole nail, with clear new nail growing in at the base. We covered polish stains in detail in dark polish and yellow nails. If your nail looks like that and passes the other 4 checks, it is most likely a stain.

Check 2: a thicker nail

A fungal nail is often thicker than usual. The easy way to check is to look from the side and compare it with the same nail on the other foot. A normal nail is thin and smooth; a thickened one looks raised and chunky. Some people notice it first when the clippers struggle to cut.

A thick nail does not only come from fungus. Thick, overgrown nails can be linked to psoriasis or circulation problems, and says nails that turn yellow, thicken and seem to stop growing can be a sign of something going on inside the body. Whatever the cause, a thicker nail is one for a doctor to see.

Check 3: brittle, crumbly nail with debris underneath

A fungal nail is often brittle, cracking, splitting or crumbling, with buildup under the nail. The edge may crumble and look ragged. Shine your phone torch under the tip of the nail. If you see packed white or yellow debris under it even after washing, that is this sign.

That is different from ordinary brittle nails from dry skin or lots of water, which usually peel in layers at the tip but keep their colour, stay thin, and have nothing packed underneath. You can read about those in brittle nails: causes and care.

Check 4: the nail lifting away

Look at the tip of the nail and see whether the cloudy white part is getting wider. That is where the nail has lifted off the skin underneath. A fungal nail may lift so it is no longer firmly attached, and in severe cases the nail can become misshapen or fall off.

Lifting has other causes too, such as a knock or cleaning under the nail too hard. But the gap under a lifted nail is a damp space germs like, and nail lifting is one of the nail changes a doctor should examine.

Check 5: the skin around it, and the other nails

The last check is not about one nail. Look between every toe, especially between the fourth and little toes. If the skin is scaly, peeling, itchy or soggy white, it may be athlete's foot, which can spread to the nails. Then look at your other nails to see whether any are starting to change colour too. If it has spread to several nails, see a doctor.

You have checked. What does it mean?

This table is not for scoring how likely it is to be fungus. It answers one question: should you see a doctor before going to the nail salon? If you are unsure, take that as a yes.

When to see a doctor, and what happens there

See a doctor if the infection is severe, has spread to other nails, or if you have diabetes or a weakened immune system. Nail fungus is usually painless, but when severe it can damage the nail and cause pain. Pain, swelling or redness around the nail is a reason to go.

At the clinic, a doctor will examine both your fingernails and toenails and may take a sample from a nail to look at under a microscope, for example by clipping the tip, scraping the surface or collecting debris from under the nail. The result helps the doctor choose a treatment that matches the real cause.

Good to know in advance: treatment takes time. It can take a year or longer for the nail to grow out completely, medicated nail paint has to be used for about 6 to 12 months, and fungus can come back. Treatment should be chosen by a doctor, not bought and tried on a guess.

Why we do not paint over nails that might have fungus

We want to be straight with you about this, as a friend would. At Nanny Nails we do not paint over nails that are thick and yellow or that look like they might have fungus. It is not because we are put off, and it is not because we think you do not look after yourself. Nail fungus can happen to anyone.

The reason is the nail process itself. Doing nails adds moisture to the nail, from nail polish remover and from keeping the nail sealed under colour for weeks. If there is fungus in the nail, that moisture could help it spread, and the colour on top hides how the nail is changing in the meantime. You should also ask your doctor whether you can wear nail polish while treating nail fungus.

If you arrive and the nail looks like it fits the signs, we will tell you honestly and suggest seeing a doctor first. We would rather you knew before you left home, so you do not make a wasted trip and can choose to see a doctor first, then book your nails for later.

Looking after your feet while you wait

Advice you can start today, to help stop it spreading to other nails or to people at home:

• Keep feet clean and dry Dry between the toes after every shower, and change socks when they get sweaty.
• Let shoes rest Let shoes dry for about 24 hours before wearing them again. Rotating pairs helps, and breathable shoes are best.
• Wear sandals in damp shared places communal showers, changing rooms, pool decks.
• Keep nails short Cut toenails straight across, no longer than the end of the toe.
• Do not share nail clippers, towels or shoes and clean your clippers after every use.
• Treat athlete's foot at the same time if you have it, since it can spread to the nails.

And if your yellow nail does not fit the fungus signs but comes from turmeric, smoking or something else in daily life, we gathered those causes in what causes yellow nails: 7 everyday things.

When can you have your nails done again?

The shortest answer: when your doctor says so. If the test shows it is not fungus, or your doctor says it has cleared, you can have colour done as normal. Nails that are yellow from polish stain can be done straight away. We put a base coat under the colour on every job anyway, the step that helps keep dark colours from staining the nail.

After a long time keeping your feet in closed shoes, many people want something fresh. An emerald green like this makes feet in sandals look bright straight away.

Or, if you like a clean look, a soft pastel blue makes feet look brighter and is not too loud for work.

Prices include shaping, base coat and top coat. See the full menu on the services and prices page. Every job comes with our 7-day care period.

What customers say about us

Read all reviews on the reviews page.

The 5 checks in one line

Colour, thickness, surface, attachment and the skin around it. If your yellow nail is even, thin, firmly attached, clear at the base, and you often wear dark polish, it is most likely a stain. If the colour starts at the tip, or the nail is thick, crumbly, has debris underneath, is lifting, or the skin between your toes is peeling, have a doctor look before your nail appointment, because even a doctor needs to test a sample to be sure. Purple, black or dark-lined nails are a different topic, covered in a black line or a purple nail: bruise or doctor?, and for toenail colours to save for when your nails are ready, browse the gallery.

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