A discoloured or thickened toenail isn't always toenail fungus. Injury, psoriasis, nail polish staining, a lifted nail, ordinary ageing and a bruise under the plate all look similar at a glance. In one analysis of 35,257 nail samples sent for testing, more than half came back negative for fungus.
Written and reviewed by Dr. Evan Lewis, PhD. Last updated August 5, 2026.
We should say plainly that we sell an iodine foot care product, so you can weigh this accordingly. We also don't sell a drug, which means we have no reason to tell you your nail is fungal when it might not be. That's the whole reason this page exists.
The short version
- Where the change starts and which way it travels tells you more than the colour does.
- Fungus creeps up from the free edge or a side fold. An injury sits still and moves outward as the nail grows.
- One nail suggests injury. Several nails suggests fungus or psoriasis.
- Pinprick dents across the surface point at psoriasis, not fungus.
- A clipping sent for testing settles it. Nothing you can do at home is definitive.
Why so many people get this wrong
Nail changes are hard to read, and not only for the person they belong to. A 2018 comparison study published in Dermatology Research and Practice checked how often a clinician's visual diagnosis of fungal nail matched the lab result. Mean accuracy was 75.4%. Dermatologists were right 75.3% of the time and podiatrists 80.8%.
So roughly one nail in four that a trained professional looks at and calls fungal isn't. If they're wrong that often with the nail in front of them, a photo on your phone at eleven at night is a coin toss.
The bigger number comes from the lab side. A 2023 JAAD International review of 35,257 fungal nail cultures from a US national laboratory found 51.1% were negative for fungus. Those were nails somebody thought were worth testing.
And fungal infection accounts for around half of all nail disease, per a review in Canadian Family Physician. The other half is everything else on this page.
What does toenail fungus actually look like?
A fungal nail usually starts small and at one end. The NHS describes nails that become brittle, discoloured or thicker than usual, with the change beginning at the nail edge and spreading inward until the whole nail turns white or yellow.
Three things go together. Colour, usually yellow, white or brown. Thickness, so the nail resists the clippers. And crumbling, so the tip breaks up into powder rather than cutting cleanly.
It's slow. Months, not days. It's often painless. And it frequently shows up in more than one nail, because whatever is on one toe is in the same shoe as the others.
What else looks exactly like it?
Six things come up over and over. Here they are side by side.
| What it could be | Where it starts | Colour and texture | How many nails | The giveaway |
|---|---|---|---|---|
| Fungus | Free edge or a side fold | Yellow, white or brown. Thick, crumbly at the tip | Often several | It creeps toward the cuticle over months, with no injury behind it |
| Injury or a bruise | Wherever the knock landed | Red, purple or black. Smooth, with a defined edge | Usually one | It keeps its size and shifts toward the tip as the nail grows |
| Nail psoriasis | The matrix, so it appears mid-plate | Pinprick dents plus a salmon or tan patch | Several, fingers too | Pitting. Fungus doesn't pit |
| Nail polish staining | Everywhere the polish sat | Even yellow or orange. Normal thickness | Every nail that was painted | It appeared the day the polish came off, and the nail still cuts normally |
| A lifting nail | The free edge, working back | White or grey where air has got underneath | One or several | The pale area is a gap, not a stain. It's hollow underneath |
| Ageing and pressure | The whole plate, slowly | Dull, yellowish, ridged. Uniformly thick | Big toes first | It's thick but not crumbly, and it's been creeping on for years |
Two honest caveats. These overlap. And you can have more than one at once, which is the single most common reason people go round in circles. Psoriasis damages the plate, and fungus is perfectly happy to move into a damaged plate afterwards.
Three questions that narrow it down fastest
How many nails are involved?
One nail, with the other nine fine, leans hard toward injury. Several nails leans toward fungus or psoriasis. Every nail that was painted, and none that weren't, is polish.
Was there an injury you can name?
A stubbed toe, a dropped weight, a downhill hike, a marathon, a season in football boots. If you can name the day, you probably have your answer. Trauma is also cumulative, so shoes half a size too short count even though nothing dramatic happened.
Which end did it start at?
This is the most useful question on the page and almost nobody asks it. Fungus works from the outside in, arriving at the free edge or a side fold and travelling toward the cuticle. Injury does the opposite, because the mark is stuck to the plate and the plate is moving outward at about 1.6mm a month. Watch the same nail over eight weeks and take a photo each fortnight. If the patch is drifting toward the tip with clean nail behind it, that's growth pushing an old injury out.
When should you stop guessing and get it checked?
Book with a chiropodist, podiatrist or your doctor if:
- The toe is painful, hot, swollen or bleeding
- There's a dark streak running from the cuticle toward the tip, or the skin beside the nail is going darker
- The change came on suddenly, or it's moving fast
- You have diabetes, poor circulation or reduced feeling in your feet
- You've been treating it as fungus for six months and nothing has shifted
A clipping sent for testing is the only way to know for certain, and it's a two minute appointment. Here's the difference between a chiropodist and a podiatrist if you're not sure who to book.
That last point about a dark streak matters. The American Academy of Dermatology lists a new or changing dark band in a nail, darkening skin next to the nail, and a nail separating from its bed as reasons to have a dermatologist look. Most dark marks under a nail are old bruises. It's still worth ten minutes of somebody's time.
What if it does turn out to be fungus?
Then the thing to get straight first is the calendar, not the product. A toenail grows roughly 1.6mm a month, so a big toenail takes about 9 to 12 months to fully replace itself. The nail you have now doesn't get better. It gets replaced. That's why the NHS says topical treatments need 6 to 12 months of use.
Anyone promising you a fast result on a toenail is either selling something or hasn't looked at how nails grow. Take a photo every two weeks and judge by the new growth at the base, not by the old nail at the tip.
On the routine itself, we build EZ Clear Nails around a soak tray rather than a brush for one reason: reach. It's two ingredients, elemental iodine and pure water, and submerging the toe carries liquid under the free edge and into the side folds, which is exactly where a paint-on film sits on top instead of getting in. Iodine has been used on skin since the 1800s, and this is the routine that 200+ foot care clinics across North America send home with patients.
If your nail turns out to be an old bruise or a polish stain, you don't need us. Read the relevant page below and go and enjoy your evening.
Work out which one you're looking at
Each of these takes one of the six and goes deep on it.
- Toenail fungus vs trauma, if you can remember a knock or you run
- Nail fungus vs nail psoriasis, if the surface is dented or you have psoriasis anywhere else
- Nail polish stain or fungus, if you noticed it the day the polish came off
- Toenail separating from the nail bed, if part of the nail has gone pale and hollow
- Do thick toenails always mean fungus, if thickness is the main change
- Black toenail, if the mark is dark rather than yellow
And if the thing you're looking at is on the sole of your foot rather than a nail, that's a different family of questions. Start with is it a corn or a wart, which covers how a wart differs from a corn and a callus.
Common questions
How do I know if it's toenail fungus or just a damaged nail?
Look at direction and count. Fungus starts at the free edge or a side fold and creeps toward the cuticle over months, usually across more than one nail, with no injury behind it. Damage sits still, keeps its size, and drifts toward the tip as the nail grows out, usually in one nail you knocked.
Can a toenail look like fungus but not be fungus?
Yes, and often. In an analysis of 35,257 nail samples sent to a US laboratory, 51.1% were negative for fungus. Psoriasis, injury, polish staining, a lifting nail and ordinary age-related thickening all produce yellow, thick or discoloured nails that look fungal to the naked eye.
What is the fastest way to tell if a toenail is fungal?
There isn't a fast home test that's reliable. The quickest honest answer is a clipping sent for testing by a chiropodist, podiatrist or doctor, which usually takes one short appointment. At home, the most useful check is watching the same nail for eight weeks and photographing it every fortnight to see which way the change is moving.
Does a thick toenail always mean fungus?
No. Nails thicken from years of pressure in shoes, from a single hard knock that damaged the growth plate, from psoriasis, and simply from age. Fungal thickening usually comes with crumbling at the tip and colour spreading from the edge. Thickening on its own, in a nail that still cuts cleanly, often isn't fungal.
Should I treat it as fungus while I wait to find out?
A daily foot care routine is sensible either way, since clean, dry, well-trimmed nails help whatever is going on. What isn't sensible is starting an oral medication or assuming a diagnosis before it's confirmed, particularly if you've already spent months on something that hasn't shifted.
Is toenail fungus contagious to other people?
Fungal nail infections can pass between people through shared floors, towels and footwear, which is why gym showers and changing rooms come up so often. That's another reason worth confirming what you actually have, since an old bruise or a polish stain isn't going anywhere near anyone else.
Dr. Evan Lewis, PhD, specializes in natural and nutritional therapies for the prevention and management of chronic diseases and their complications. His research spans chronic disease, diabetes complications, clinical nutrition and nerve health, including the development of topical iodine therapy for foot care and wound health. IodinePure products are listed with Health Canada as cosmetics. This article is general information about nail appearance and is not a diagnosis.
