Toenail fungus typically starts as a white or yellow-brown spot under the tip of the nail. As the infection spreads, the nail thickens, becomes discolored across a wider area, and develops brittle or crumbly edges. The changes are gradual, which is why many people don’t notice the infection until it’s well established.
Early Signs to Watch For
The first visible clue is usually a small spot of discoloration near the free edge of the toenail. It can be white, yellowish, or yellow-brown. At this stage, the nail still feels relatively normal in thickness and texture, and the spot is easy to dismiss as a scuff or stain. This early phase typically lasts about four to six weeks before the infection becomes more obvious.
During this window, the fungus is working its way into the nail bed from the tip, slowly migrating toward the cuticle. You might also notice a faint white line or haze just beneath the nail surface that wasn’t there before.
What Moderate Infection Looks Like
Over the next two to three months, the discoloration spreads and the nail begins to thicken noticeably. The color may shift to a deeper yellow or brown, and chalky debris starts to accumulate underneath the nail. This buildup of keratin and dead cells pushes the nail upward and can cause it to separate from the nail bed, a process you’ll see as a widening gap between the nail and the pink skin beneath it.
At this point, the nail edges often look ragged or uneven, and the nail itself may feel rougher when you run a finger across it. Some people notice a mild odor, especially after removing socks or shoes at the end of the day.
Advanced and Chronic Stages
After about six months of untreated infection, toenail fungus enters an advanced stage. The nail becomes severely thickened, misshapen, and may crumble apart when you try to trim it. Colors range from dark yellow to brown, and in some cases the nail takes on a greenish or blackish tint if bacteria have joined the fungal infection.
In chronic cases (roughly a year or more), the nail can detach almost entirely from the nail bed. Walking may become uncomfortable because the thickened, distorted nail presses against the inside of your shoe. There’s also a higher chance the infection will spread to neighboring toenails. At this stage, the nail may not grow back normally even after the fungus is treated.
Two Common Patterns of Infection
Not all toenail fungus looks the same. The most common pattern starts at the tip or side of the nail and works backward toward the cuticle. You’ll see yellowing and thickening that progressively covers more of the nail, with debris building up underneath. This is the classic presentation most people picture when they think of toenail fungus.
A second pattern, called white superficial infection, looks quite different. Instead of yellow discoloration deep in the nail, you’ll see well-defined white patches, sometimes described as “white islands,” on the surface of the nail itself. These spots are opaque and chalky. Over time, they merge until the entire nail surface appears white and powdery. The nail becomes soft and crumbly rather than hard and thickened. This type stays on the surface of the nail plate rather than burrowing underneath it, which makes it easier to treat.
Fungus vs. a Bruised Toenail
Dark discoloration under a toenail isn’t always fungus. A bruise (from stubbing your toe or wearing tight shoes) produces a reddish or purplish spot that darkens to deep brown or black. Fungal infections, by contrast, tend to be yellow to medium brown. The key difference is movement: a bruise grows out with the nail over weeks, slowly shifting toward the tip until it’s eventually trimmed away. A fungal spot stays put or spreads.
If you have a dark spot under your nail with no obvious injury to explain it, and it isn’t growing out over time, that warrants a closer look from a professional.
Fungus vs. Nail Psoriasis
Psoriasis can affect toenails in ways that mimic fungus, including thickening, discoloration, and separation from the nail bed. A few visual clues help tell them apart. Psoriasis tends to cause small, distinct pits or dents on the nail surface, like tiny pinpricks. More than 10 pits on a single nail strongly suggests psoriasis rather than fungus. Psoriasis also produces distinctive reddish-brown or “salmon-colored” spots in the nail bed that fungal infections don’t cause.
Overlap is common, though. About one in four people with nail changes that look like fungus actually have something else going on. A Dutch study of general practice patients found that clinical visual diagnosis was correct roughly 75% of the time when compared against lab testing. That means one in four suspected fungal infections turned out to be a different condition entirely.
Skin Changes Around the Toes
Fungal infections don’t always stay on the nail. The same organisms cause athlete’s foot, which shows up as scaly, peeling, or cracked skin between the toes, particularly in the space between the fourth and fifth toes. The skin may look white and waterlogged (macerated) or red and flaky. If you have both peeling skin between your toes and nail discoloration, a fungal infection is the likely culprit for both.
When Appearance Alone Isn’t Enough
Visual identification is a good starting point, but it has limits. Lab confirmation typically involves scraping debris from under the nail and examining it under a microscope or sending it for culture. The microscope test catches about 85% of true infections, while cultures are less sensitive at around 54%. This matters because treating a condition that isn’t actually fungus with antifungal medication wastes time and money. If your nail changes are ambiguous, or if they don’t respond to initial treatment, lab testing can clarify what’s really happening.