Toenails keep a record. Tight shoes, long runs, humid summers and old injuries all leave their mark in the nail plate, and colour is usually the first thing to shift. Most discoloured toenails have an ordinary explanation behind them. A few need professional attention, and one pattern should never be waved off.

This guide covers the colours we see most at our North York clinic, what each one tends to mean, and how to tell the harmless versions from the ones worth booking about. Where a fuller article exists on a cause, it is linked so you can go deeper.

Yellow nails: the change we see most

A nail that turns yellow, thickens and starts crumbling at the free edge is the classic picture of a fungal infection. Dermatophyte fungi feed on keratin, the protein the nail is built from, and the debris that accumulates under the plate gives it a yellow-brown cast. Our fungal toenail treatment guide explains how infections are confirmed and what a chiropodist can actually do about them.

Fungus is not the only explanation. Dark polish worn back to back for months stains the plate. Nails yellow gradually with age. Psoriasis and some other skin conditions alter nail colour and texture too. The full list lives in our article on yellow toenails, and this piece on how fungal infections start covers avoiding the most common cause in the first place.

White flecks, patches and streaks

Scattered white flecks are old news. They mark small knocks to the nail root from weeks earlier, often a stubbed toe you have long forgotten, and they simply grow out. Nothing to treat, nothing to correct.

Two white patterns earn a closer look. A chalky patch sitting on the surface of the nail that slowly spreads can be a superficial form of fungal infection, one of the easier forms to clear when caught early. A rough, dry white area revealed when long-worn polish comes off is keratin granulation, surface damage rather than infection; a break between polish applications gives the plate time to recover.

Black or deep purple under the nail

The usual cause of a black toenail is blood trapped underneath, what runners call black toe. Long descents, sports with hard stops and shoes with a shallow toe box let the nail knock against footwear hundreds of times an hour, and a bruise forms under the plate. It can throb for a day or two, then settles, and the mark drifts outward as the nail grows over several months. If fresh pressure under a nail is genuinely painful, a clinician can relieve it safely. Home methods involving heated implements are a reliable way to trade a bruise for an infection.

A different pattern needs prompt attention: a dark band running lengthwise from the base of the nail to its tip that is new, wider than a few millimetres, widening over time, or spreading pigment onto the skin at the edge of the nail. Melanoma occasionally begins under a toenail, and outcomes are far better when it is found early. A streak with no injury behind it is not an emergency, but it is a reason to be seen soon rather than watched for months.

A green tinge at the edge

Green usually means bacteria rather than fungus. When a nail lifts slightly from its bed, after an injury or long stretches in damp footwear, a moist pocket forms underneath, and Pseudomonas bacteria that settle there produce a distinctive green-blue pigment. It looks alarming, but it is very treatable: the lifted portion is trimmed back, the area is kept dry, and the colour goes with it. A green patch that keeps returning is a reason to have the nail assessed, since something is keeping it lifted.

Red, swollen skin beside the nail

Sometimes the nail keeps its colour and the skin beside it changes instead. A red, hot, tender nail fold, most often on a big toe, points to an ingrown nail pushing into the skin, and once infection sets in it tends to get worse rather than better on its own. Our ingrown toenail treatment guide walks through the options, and if you are weighing a permanent fix, the Onyfix versus surgery decision guide compares the two paths.

Sorting the harmless from the serious

A chiropodist starts with what changed and when, what you wear on your feet, and how the rest of the nail and surrounding skin look. When a fungal infection is suspected, a clipping can be sent for lab confirmation, since antifungal treatment takes months and it is worth knowing the diagnosis is right before starting. A new or spreading colour change is a good reason to book a foot assessment, and if thickened, discoloured nails have become hard to cut, regular medical foot care keeps them manageable.

One group should skip the wait-and-see step entirely. If you live with diabetes, any new discolouration, particularly with swelling, warmth or an odour, deserves prompt professional attention, because reduced sensation can hide a problem that is further along than it feels.

Frequently Asked Questions

My toenail turned dark after a weekend hike. Do I need it looked at?

If the toe took repeated pressure inside a boot and the dark area sits under the nail like a bruise, it will usually grow out over several months without treatment. Painful pressure in the first day or two can be relieved in clinic. Book an assessment if the darkness appeared without any activity you can point to, forms a lengthwise band, or spreads onto the skin around the nail.

Can nail polish really stain a toenail yellow?

Yes. Pigments in darker polishes bond to the surface of the plate, and months of back-to-back wear can leave nails yellowed and dry. The stain grows out once the nail gets a break. If the yellow comes with thickening or crumbling, or it lingers weeks after you stop wearing polish, have it checked for fungus.

Which colour changes should send me to a clinic quickly?

A new dark streak running the length of the nail, pigment spreading onto the surrounding skin, green or yellow discolouration accompanied by pain, swelling or discharge, and any change at all if you have diabetes or poor circulation. Everything else can wait for a routine appointment, though none of it is a waste of one.

Will cutting away the green part of a nail fix it?

Trimming back the lifted, discoloured section removes the moist pocket the bacteria live in, and keeping the area dry usually stops it returning. Do not dig at it at home if the nail is firmly attached or the skin is sore. A chiropodist can trim it safely and check whether something underneath, such as fungus, is keeping the nail lifted.

If a toenail has changed colour and you are not sure why, a single visit usually settles it. Book an assessment at Don Wood Foot Clinic in North York and get an answer instead of a guess.