Toenail fungus typically starts as a white or yellow-brown spot under the tip of the nail. As the infection progresses, the nail thickens, becomes discolored, and begins to crumble at the edges. The appearance changes significantly depending on how far along the infection is and which type you’re dealing with, so here’s what to look for at every stage.
The Earliest Signs
The first thing most people notice is a small spot of discoloration near the tip or side of the toenail. It’s usually white or yellowish-brown, and it’s easy to dismiss as a scuff mark or minor bruise. At this point the nail still feels normal in thickness and texture. The spot sits underneath the nail surface rather than on top of it, which is one way to distinguish it from a simple stain.
Within weeks to months, that spot tends to spread. You might see yellow streaks running through the central portion of the nail, or the white area slowly expanding toward the base. The edge of the nail may start to look slightly ragged or uneven, even if you haven’t bumped it against anything.
How It Looks as It Progresses
Once the fungus moves deeper, the changes become harder to ignore. The nail thickens noticeably, sometimes enough that it presses uncomfortably against the inside of your shoe. The color shifts from pale yellow to a deeper yellow-brown, and the texture turns brittle and crumbly. Pieces of the nail may break off unevenly, leaving a ragged, uneven edge.
Scaling and debris start to build up underneath the nail. This trapped material pushes the nail upward and can make it look raised or distorted. The debris itself is usually whitish or yellowish and has a chalky, powdery consistency. In many cases, the nail develops a noticeable smell, often described as musty or foul.
One of the more distinctive signs at this stage is nail separation. The nail begins to lift away from the nail bed, creating an abnormal border between the pink area and the white edge. That border often looks wavy or irregular, with the white portion thicker in some spots and thinner in others. The space underneath may appear gray, green, yellow, or even purple depending on the type of fungus and any secondary bacteria present.
The Three Main Patterns
Not all toenail fungus looks the same. The infection takes different forms depending on where the fungus enters the nail.
- Starting at the tip or sides: This is the most common pattern by far. The infection begins at the free edge of the nail and works its way backward. You’ll see yellowing, thickening, and crumbling that starts at the tip and gradually creeps toward the cuticle. Yellow streaks or yellow patches in the center of the nail plate are characteristic.
- White surface infection: Instead of getting under the nail, the fungus colonizes the top surface. This creates a chalky white scale that slowly spreads across the nail. The surface feels rough or powdery to the touch. It’s less common but easier to treat because the fungus hasn’t penetrated deeply.
- Starting near the cuticle: The least common pattern. Discoloration and thickening appear near the base of the nail, close to the half-moon shape, and spread outward. This type is more often seen in people with weakened immune systems.
In the most advanced cases, the entire nail becomes involved. The nail turns opaque and yellow-brown throughout, thickens dramatically, and becomes so friable that it crumbles apart. At this stage the nail may be misshapen or partially destroyed.
Fungus vs. Other Nail Problems
Several conditions mimic toenail fungus, and roughly half of abnormal-looking toenails turn out to be something else entirely.
Nail psoriasis is the most common lookalike. Both conditions cause discoloration, thickening, and nail separation. The key visual difference: psoriasis tends to produce small dents or pits across the nail surface, along with horizontal grooves and reddish-brown spots that look like drops of oil under the nail. Fungal nails don’t pit. They crumble and build up debris underneath, while psoriatic nails tend to thin and flake.
A bruise under the nail (from stubbing your toe or tight shoes) can also cause dark discoloration that looks alarming. But a bruise is typically reddish-purple or black, stays in one area, and gradually grows out with the nail over several months. It doesn’t cause thickening, crumbling, or the yellow-brown color shift that fungus produces.
Simple aging can thicken and yellow toenails too, especially on the big toe. The difference is that age-related changes tend to affect multiple nails evenly, while fungal infections often start in one nail and spread to others over time.
What Each Color Tells You
The color of the affected nail carries useful information. White or pale yellow early on usually signals a straightforward fungal infection. Deeper yellow-brown suggests the infection has been established for a while and has penetrated further into the nail. A greenish tint often means bacteria have moved into the space created by the lifting nail, sometimes alongside the fungus. Dark brown or black discoloration warrants closer attention, since it can indicate a bruise, melanoma, or certain mold infections rather than typical fungus.
Signs the Infection Is Getting Worse
Fungal nail infections don’t resolve on their own. Without treatment, a mild case gradually becomes moderate and then severe over months to years. Here’s the typical trajectory of what you’d see:
- Mild: A spot of discoloration at the tip, minimal thickening, nail still mostly intact.
- Moderate: Yellow streaks or patches covering a third to half the nail, noticeable thickening, early crumbling at the edges, some debris buildup underneath.
- Severe: The entire nail is discolored and opaque, significantly thickened, crumbling or breaking apart, with substantial debris underneath. The nail may be partially detached or misshapen. A thick, localized lump of infection within the nail plate can develop at this stage.
The infection also tends to spread to neighboring toenails. If you notice one nail changing and a second nail developing a similar spot weeks or months later, that pattern is highly suggestive of fungus rather than trauma or another cause. The big toe and little toe are the most commonly affected, partly because they take the most pressure and friction inside shoes.