Nail fungus or something else: how to tell the difference

Let’s start with what this article won’t give you: a product to buy or a home remedy to try. I’m a nail technician, not a doctor, and onychomycosis — the medical name for nail fungus — is confirmed by a laboratory test, not by comparing your nail to photos online.

What I can tell you is what it looks like, what gets mistaken for it, why no salon should work on that nail, and at what point you stop reading and book a doctor.

What nail fungus looks like

Usually several signs appear together:

Colour. The nail turns yellow, grey or brown. A common form begins at the free edge or the side, but superficial and proximal forms exist too — so it is not correct to say fungal infection never begins near the base of the nail.

Texture. The plate crumbles, splits into layers, roughens.

Thickness. The nail thickens, sometimes dramatically, and loses its translucency.

Separation. A cavity forms between plate and nail bed, holding crumbly debris.

Odour. Unpleasant, faintly sweet. Appears in advanced cases.

One sign alone means nothing. A combination that doesn’t improve justifies a test — waiting for it to spread to neighbouring nails is not necessary, and the absence of itching or smell does not rule infection out.

Four things mistaken for fungus

This is the useful part, because most suspicions turn out to be something else.

Trauma. A knock or a crush — the nail goes white or dark in one spot, and the mark grows out over months. It doesn’t spread.

A green stain under gel. Forms where product lifted and moisture sat underneath. Greenish, sharply outlined, and it stays on the plate after the material comes off. Green discolouration is bacterial — typically Pseudomonas, particularly where the plate has lifted. It is not fungus. Whether anything else is going on, and what to do next, is a doctor’s call; promising that it will always harmlessly grow out is not appropriate.

Staining from dark polish. Pigment soaks into the top layer. The nail is otherwise smooth and strong. Fades in a few weeks.

Nail psoriasis. Pitting, ridging, change of shape. Looks similar, is a different condition, and belongs to a dermatologist.

White patches and dark bands. White marks have several possible causes. A new or changing dark longitudinal band needs medical assessment rather than an assumption that it is a bruise or fungal infection.

Add one more that isn’t on most lists: onycholysis — the plate separating from the bed after trauma or over-aggressive manicure. There’s a cavity, but there may be no infection at all.

Fingernails and toenails

Toenails are affected far more often, for unglamorous reasons: warmth, moisture and closed shoes. The big toe usually goes first.

Fingernails are affected less often, mostly in people whose hands stay wet or gloved for hours, or when it transfers from a foot.

Gel enhancements don’t cause fungus on their own. What can contribute is moisture trapped under lifted product that nobody dealt with in time — the mechanics are in do gel nails damage your nails.

How it’s treated

Briefly, because this isn’t my field: a doctor confirms the diagnosis from a scraping or a clipping, then chooses topical or systemic treatment based on the result. It takes months, because you’re waiting for the affected part of the nail to grow out.

Two things worth knowing in advance. Over-the-counter products used on an unconfirmed diagnosis are usually just lost time. And if you treat first and test later, the test can come back falsely negative — which is why you go to the doctor earlier rather than later.

What a salon should do

Speaking for myself and for the approach I consider correct.

I don’t work on a nail I suspect, and I don’t put gel on it. Not because it’s technically impossible — it isn’t. The problem is twofold: product hides the nail so nobody can see what’s happening underneath, and the tool used to file that nail carries material onward.

What I do instead: say what I see, explain the difference between fungus and the things that imitate it, and recommend getting it looked at. The remaining nails can usually be treated normally if they’re healthy — though that cannot be promised in advance for every case.

That isn’t turning a client away. It’s declining one procedure on one nail until there’s clarity.

Why gel doesn’t go on a suspect nail

It hides the progression. Under product, nobody can see whether things improve or spread.

Moisture stays in. The space between plate and material favours the problem rather than the nail.

Tools carry it. The file and the bit touch affected tissue.

Prevention

Tools. Single-use files and sterilised metal instruments are the baseline, and you’re entitled to ask about them. The related question of bringing your own is covered in bring your own tools.

Dry hands and feet. Especially between the toes and after sport.

Deal with lifting promptly. Product that has started to lift belongs at a refill, not on another fortnight of wear.

Your own file at home. Don’t share it, including with family.

Shoes and socks. Breathable, dry, rotated.

Quick answers

Can I identify fungus from a photo online? No. Several conditions look identical.

Can I come for a manicure if I suspect it? On the other nails, yes. On that one, not until it’s clear.

Will polish cover it up? It will hide it from view, which is the opposite of helpful.

Did gel nails cause this? Not on their own. Trapped moisture under lifted product can contribute.

When do I see a doctor? When the change spreads, the nail crumbles, or more nails become involved. For work on healthy nails, reach us through contacts.