Toenail fungus typically starts as a small white or yellow-brown spot under the tip of the nail. As the infection progresses, the nail thickens, becomes discolored, and begins to crumble or break apart at the edges. It’s extremely common, affecting an estimated 20% or more of adults over 60 and over 50% of those past 70.
Early Signs to Look For
In its earliest stage, toenail fungus is easy to miss. You might notice a slight yellowish, whitish, or brownish discoloration near the tip or side of the nail. The nail may look a little cloudy in one spot, or the edge might start to lift slightly from the nail bed underneath. There’s usually no pain at this point, and the nail still looks mostly normal, which is why many people ignore it.
The most common pattern starts at the free edge of the nail (the part you trim) and along one side, then gradually works its way back toward the cuticle. If you notice a small patch of discoloration that doesn’t grow out with the nail over a few weeks, that’s a strong hint that fungus has taken hold rather than a simple stain or bruise.
What Moderate Infections Look Like
As the fungus spreads deeper, the changes become harder to overlook. The discoloration intensifies, shifting from a faint spot to a more obvious yellow, brown, or even greenish tint that covers a larger portion of the nail. The nail itself thickens noticeably. You may find it harder to trim, and it can feel stiff or rigid compared to your healthy nails.
At this stage, the nail often turns brittle and crumbly. Pieces may break off unevenly, leaving ragged or jagged edges. You might also see chalky, powdery debris building up underneath the nail, which pushes it further away from the nail bed. Some people notice mild pain or discomfort, especially when wearing shoes that press on the thickened nail.
Advanced and Chronic Infections
Left untreated, toenail fungus can eventually distort the entire nail. In advanced cases, the nail becomes severely thickened and misshapen, sometimes curving or warping in ways that make it difficult to walk comfortably. The color may darken to deep brown or even black. Crumbling becomes more dramatic, with large sections of the nail breaking away.
The nail can separate almost completely from the nail bed, a condition that creates a visible gap between the nail and the skin underneath. A foul odor is common at this point, caused by the buildup of debris trapped beneath the nail. In chronic cases, the nail may not regrow normally even after treatment, and the infection can spread to surrounding toenails.
A Less Common Pattern: White Surface Spots
Not all toenail fungus follows the tip-to-base progression. One variant shows up as white, chalky patches directly on the surface of the nail rather than underneath it. These spots can look powdery or flaky, almost as if someone dusted the nail with white powder. The surface feels rough if you run your finger over it. This type tends to be easier to treat because the fungus hasn’t burrowed deep beneath the nail.
Fungus vs. a Bruised Toenail
A dark spot under a toenail doesn’t always mean fungus. If the discoloration is black and shiny, especially after you stubbed your toe or wore tight shoes during a long run, it’s more likely a bruise (blood pooling under the nail). A bruise typically stays in one place and grows out with the nail over weeks or months.
The key difference is what’s happening between the nail and the skin beneath it. Fungal infections cause the nail to separate from the nail bed, giving the discolored area an opaque, cloudy look. A bruise keeps the nail attached, so it still looks somewhat translucent around the dark spot. Color is another clue: yellow, gray, or greenish tints point toward fungus, while a shiny dark red or black spot points toward trauma.
Fungus vs. Nail Psoriasis
Psoriasis can affect toenails in ways that look surprisingly similar to a fungal infection, including thickening, discoloration, and lifting from the nail bed. Both conditions can cause pitting (tiny dents in the nail surface) and structural damage.
A few details help tell them apart. Fungal infections tend to darken the nail progressively and often produce a foul smell. Nail psoriasis more commonly causes yellowing with a chalky white buildup underneath. Psoriasis also tends to affect multiple nails at once and often shows up alongside skin symptoms like scaly patches on the elbows, knees, or scalp. If you have both nail changes and skin symptoms, psoriasis is worth considering. A doctor can confirm the diagnosis with a nail clipping sent to a lab, since the two conditions occasionally overlap.
What Each Color Means
- White or off-white: Often an early infection, or the surface-level variant where fungus grows on top of the nail.
- Yellow to yellow-brown: The most classic sign of toenail fungus, especially when it starts at the tip and spreads inward.
- Green or greenish: Can indicate a bacterial infection layered on top of a fungal one, particularly when moisture is trapped under the nail.
- Dark brown or black: Seen in advanced fungal infections, though a shiny black spot is more likely a bruise. Persistent dark discoloration that doesn’t grow out warrants a closer look.
Signs That It’s Getting Worse
Toenail fungus doesn’t resolve on its own. If you’re watching a nail and wondering whether it’s progressing, these are the signals that the infection is advancing: the discolored area is expanding rather than staying the same size, the nail is getting thicker or more difficult to cut, debris is accumulating underneath, or the nail is pulling away from the bed more noticeably. Pain during walking, a worsening smell, or discoloration appearing on neighboring nails all suggest the infection is spreading and becoming harder to treat.
Early-stage infections respond best to treatment, whether topical or oral. The longer the fungus has to penetrate the nail, the more structural damage it causes, and in some chronic cases the nail never fully returns to its original appearance.