Nail fungus typically starts as a small white or yellow-brown spot under the tip of a toenail or fingernail. As the infection spreads deeper, the nail discolors, thickens, and begins to crumble at the edges. The changes happen gradually over weeks to months, so early signs are easy to miss or dismiss as a cosmetic issue.
Early Signs to Watch For
The first visible clue is usually a small discolored spot near the free edge of the nail, the part farthest from your cuticle. It may look white, yellowish, or yellow-brown, and it often appears on just one nail. At this stage, the nail still feels relatively normal in thickness and texture. Many people assume they’ve just bumped their nail or that it’s a stain.
Over time, that spot expands. You might notice yellow streaks running through the center of the nail plate, or a yellowish area where the nail starts to pull away from the skin underneath. That separation between nail and nail bed is one of the hallmark signs. If you press gently on the nail and it feels hollow or loose at the tip, fungus is a likely cause.
How the Color Changes Over Time
Yellow is the most common color associated with nail fungus, and for good reason: when toenails turn yellow, a fungal infection is usually to blame. But fungus doesn’t always stay yellow. Depending on the type of organism involved and how long the infection has been present, you may see a range of colors.
- White: Chalky white patches on the surface of the nail often indicate a superficial type of fungal infection. These patches can have a powdery or rough texture that you can sometimes scrape off.
- Yellow to yellow-brown: The most common presentation. The discoloration tends to start at the tip and work its way back toward the cuticle.
- Brown: Deeper or longer-standing infections can turn nails brown. Brown streaks running lengthwise on the nail can also be caused by injury, certain medications, or in rare cases melanoma, so brown discoloration is worth getting checked.
- Black: A black toenail is most often a bruise under the nail from trauma. Fungal infection is a less common cause, but it can happen. Black discoloration can also, rarely, signal melanoma.
- Green: A greenish tint usually points to a bacterial infection rather than a fungal one. Bacteria that thrive in moist environments are typically responsible for green-nail syndrome.
Changes in Texture and Shape
Color changes are the most obvious sign, but what the nail feels like matters just as much. As fungus takes hold, debris builds up underneath the nail plate. This pushes the nail upward, making it noticeably thicker than your healthy nails. A fungal nail can become so thick that it’s difficult to trim with standard clippers.
The edges of the nail often become brittle and crumbly. Instead of a smooth, clean edge when you clip your nail, pieces break off in irregular chunks. The surface of the nail may develop ridges or a rough, uneven texture. In more advanced cases, the entire nail can become fragile, cracked, and distorted in shape. Some people also notice a distinct, slightly foul odor coming from the infected nail, caused by the buildup of fungal debris underneath.
Where the Infection Starts Matters
Most nail fungus begins at the tip and outer edges of the nail, then gradually works inward and back toward the cuticle. This is the most common pattern, and it accounts for the majority of cases. You’ll see the discoloration and thickening concentrated at the far end of the nail first.
Less commonly, the infection can start at the base of the nail, near the cuticle. When fungus enters from this direction, the discoloration and thickening appear closest to the skin fold at the bottom of the nail and spread outward. This pattern is more frequently seen in people with weakened immune systems.
A third type affects only the surface of the nail. Instead of burrowing underneath, the fungus sits on top, creating white, chalky, or powdery patches. These patches may cover small areas at first and eventually spread across the nail surface. This type is generally easier to treat because it hasn’t penetrated deeply.
What Advanced Nail Fungus Looks Like
Left untreated for months or years, nail fungus can destroy the nail entirely. The nail plate becomes extremely thick, deeply discolored (often dark yellow or brown), and so brittle that large sections break away on their own. The nail may separate almost completely from the nail bed, leaving it loose and painful. In the most severe cases, the recognizable shape of the nail is gone altogether, replaced by a mass of crumbling, thickened debris. At this stage, the nail bed itself may be visibly damaged, making regrowth slow and sometimes incomplete even after treatment.
Fingernails vs. Toenails
Fungal infections are far more common on toenails than fingernails. Toes spend more time in warm, damp environments inside shoes and socks, which is exactly where fungi thrive. When fungus does affect fingernails, a yeast organism called Candida is often involved rather than the typical fungal species that target toes. Yeast infections on fingernails can also signal that the immune system isn’t functioning at full strength.
The visual signs are similar on both hands and feet: discoloration, thickening, crumbling, and separation from the nail bed. But toenail infections tend to progress more slowly because toenails grow at roughly half the rate of fingernails, giving the fungus more time to establish itself before the damaged nail grows out.
How to Tell It Apart From Nail Psoriasis
Nail psoriasis can look strikingly similar to nail fungus, with thickening, discoloration, and crumbling that are hard to distinguish at a glance. A few visual clues can help you tell them apart.
Psoriasis often causes pitting: small, shallow holes or dents scattered across the nail surface. Fungal infections don’t typically produce pitting. Psoriasis also tends to affect multiple nails at once and is more common on fingernails, while fungus usually starts in a single toenail and may spread to neighboring nails over time.
One practical difference: fungal nails often have a noticeable odor from the infection brewing under the nail, while psoriasis typically does not smell. If you’re unsure, a doctor can take a small clipping of the nail and test it to confirm whether fungus is present. This simple test matters because the treatments for fungus and psoriasis are completely different, and using the wrong one wastes time while the nail continues to deteriorate.