Nail fungus typically starts as a white or yellow-brown spot under the tip of a fingernail or toenail. As the infection spreads deeper, the nail thickens, becomes discolored, and begins to crumble or break apart at the edges. It’s the most common nail disorder in adults, affecting up to 20% of people at some point in their lives, and it can look quite different depending on where and how the fungus takes hold.
The Earliest Signs
In its earliest stage, nail fungus is easy to dismiss. You might notice a small spot of white or yellowish discoloration near the tip or along one side of the nail. The nail still feels normal at this point, and there’s no pain. The spot doesn’t go away on its own, though. Over weeks or months, it slowly expands toward the base of the nail.
One of the first functional changes is a loss of the nail’s natural shine. The surface starts to look dull or slightly cloudy in the affected area. The nail may also feel rougher to the touch, even before any obvious thickening begins.
How It Looks as It Progresses
Once the fungus moves deeper, the changes become harder to ignore. The nail thickens noticeably and may feel heavy or stiff compared to your other nails. The color shifts from that initial spot to broader streaks or patches of yellow-white, brown, or even greenish discoloration. The edges of the nail become brittle, chipping or crumbling when you trim them. In more advanced infections, the nail can warp in shape, curving or developing an uneven surface.
You may also notice a buildup of soft, chalky debris underneath the nail. This debris is a mix of dead skin cells and fungal material collecting between the nail plate and the nail bed. It pushes the nail upward, making it look raised, and gives the nail an opaque, cloudy appearance from above. Eventually, the nail can start to separate from the skin underneath, beginning at the tip and working its way back. The separated area often looks white or yellowish because air fills the gap where the nail no longer attaches.
In severe cases, the nail becomes so distorted and thickened that wearing shoes is uncomfortable. The nail may give off a slightly foul smell from the trapped debris.
Different Patterns of Infection
Not every fungal nail infection looks the same. The appearance depends partly on how the fungus enters the nail.
- Starting at the tip or sides: This is the most common pattern. Discoloration and thickening begin at the free edge of the nail and move backward toward the cuticle. Nails chip, become misshapen, and turn yellow-white or brown-black over time.
- White powdery patches on the surface: Some infections affect only the top layer of the nail plate. Instead of thickening, the nail develops chalky white patches or streaks across its surface that look almost powdery. You can sometimes scrape these patches off with a fingernail.
- Milky white throughout: A less common pattern where the nail develops a diffuse milky white color with small indentations and a tendency to split into layers, but without the typical thickening or crumbling.
- Starting at the base: Rarely, infection begins near the cuticle and produces white discoloration that spreads outward as the nail grows. This pattern is uncommon in healthy individuals and can signal a weakened immune system.
Yeast Infections Look Different
When the cause is yeast rather than the more typical mold-like fungi, the infection often involves the skin around the nail as well. The nail fold (the skin that frames the base and sides of the nail) becomes swollen, red, and tender. This swelling can persist for weeks or months, and several fingers or toes may be affected at once. Over time, the nail itself starts growing in with ridges or a wavy texture, and it may turn yellow or green. The nail becomes dry and brittle. This pattern is more common in people whose hands are frequently wet, like dishwashers, bartenders, or healthcare workers.
Nail Fungus vs. a Bruise Under the Nail
A dark spot under a toenail can be either trapped blood from an injury or a fungal infection, and the two look different if you know what to check. A bruise (blood pooling under the nail) tends to appear black and shiny, and you can usually remember stubbing your toe or dropping something on it. Fungal discoloration leans yellow, gray, or greenish.
The key distinction is whether the nail has separated from the skin underneath. If the discolored area looks opaque and you can see or feel a gap between the nail and the nail bed, that points toward fungus. If the nail is still firmly attached and there’s no opacity, a bruise is the more likely explanation. A bruise also grows out with the nail over several months, while fungal discoloration stays put or expands.
Nail Fungus vs. Nail Psoriasis
Psoriasis can affect nails in ways that overlap visually with fungus, which makes these two easy to confuse. Both can cause thickening, yellow-brown discoloration, shape changes, and separation of the nail from the bed. The conditions can even occur together.
A few features lean more toward psoriasis: small pits or dents scattered across the nail surface (like someone poked it with a pin), and similar skin changes elsewhere on the body, especially around the elbows, knees, or scalp. Fungal infections are more likely to produce crumbling edges, debris buildup under the nail, and green or white discoloration rather than the salmon-colored “oil drop” patches that psoriasis sometimes creates beneath the nail. If you have signs of both, a doctor can take a small clipping of the nail and test it to confirm whether fungus is present.
Which Nails Are Most Affected
Toenails are far more commonly affected than fingernails, and the big toenail is the usual starting point. Toenails grow slowly (about 1 millimeter per month), which gives the fungus time to establish itself. The warm, moist environment inside shoes also favors fungal growth. Fingernail infections do occur but are more often linked to yeast and tend to involve the skin around the nail as well.
Fungal infections rarely affect every nail at once. If all of your nails are changing color or texture simultaneously, that’s worth investigating for other causes like psoriasis, circulation problems, or nutritional deficiencies rather than assuming it’s all fungus.