An infected toenail typically shows discoloration, thickening, or swelling around the nail, but the exact appearance depends on what’s causing the infection. Fungal infections, bacterial infections, and certain bacterial overgrowths each look distinctly different. Knowing which visual signs match which type of infection helps you figure out what you’re dealing with and how urgently you need to address it.
Early Signs of a Fungal Infection
Toenail fungus is the most common type of nail infection, and it usually starts small. The first thing you’ll notice is a white or yellow-brown spot under the tip of the nail. At this stage, the nail still feels normal in thickness and texture. Many people dismiss it as a scuff mark or minor discoloration.
As the fungus spreads, the nail thickens and turns yellow, and you may see chalky debris building up underneath the nail plate. The nail can start to separate from the nail bed, a process that makes the affected area look opaque and cloudy rather than the normal translucent pink. This separation and debris buildup is one of the hallmarks that distinguishes fungal infection from other causes of discoloration.
There’s also a surface-level form of fungal infection where a chalky white scale slowly spreads across the top of the nail. Instead of yellowing from underneath, the nail develops rough, powdery white patches that you can sometimes scrape off.
What a Bacterial Infection Looks Like
Bacterial infections around the toenail, called paronychia, look very different from fungal infections. Instead of changes to the nail itself, the problem shows up where the nail meets the skin. The skin around the nail fold and cuticle becomes red, swollen, and warm to the touch. It’s painful, often throbbing, and the swelling can develop quickly over a day or two.
As the infection progresses, pus builds up under the skin next to the nail, and a white to yellow abscess may form. If left untreated, the nail itself can start growing abnormally, developing ridges or waves. It may turn yellow or green and become dry and brittle. The key visual difference from fungus: bacterial infections cause obvious inflammation in the surrounding skin, while fungal infections primarily change the nail plate itself with little to no pain or redness in the early stages.
Green Discoloration
A green or blue-green tint on the nail is a specific sign of a Pseudomonas bacterial infection, sometimes called green nail syndrome. This bacterium produces a pigmented biofilm that sits on the surface of the nail, giving it a distinctive color you won’t see with ordinary fungus. Green nail syndrome tends to develop in nails already weakened by another problem, like an existing fungal infection, chronic inflammation around the cuticle, or a nail that has partially separated from the bed. These pre-existing conditions create openings that let Pseudomonas colonize the nail.
How to Tell Infection From a Bruise
Dark discoloration under a toenail isn’t always infection. A bruise under the nail (subungual hematoma) can look alarming, but there are reliable ways to tell it apart from fungal infection. If the dark spot is black and shiny, it’s most likely a bruise, especially if you remember stubbing your toe or dropping something on it. Bruised nails stay attached to the nail bed and remain smooth in texture.
Fungal infections, by contrast, tend to produce yellow, gray, or greenish discoloration. The nail separates from the bed underneath, creating an opaque, cloudy appearance in the discolored area. If you can see through the nail to the skin beneath and there’s no separation, you can generally rule out fungus. If the nail looks opaque and feels thicker or crumbly in the discolored zone, infection is more likely.
Advanced Fungal Infection
When toenail fungus goes untreated for months or years, the nail can become severely distorted. It thickens dramatically, sometimes curving into a ram’s horn shape. The normal half-moon at the base of the nail disappears, and the sides of the nail develop an exaggerated curve. The nail turns deep yellow throughout, becomes extremely brittle, and crumbles at the edges. Keratin and debris pack underneath the nail, lifting it further from the bed. At this point the nail may cause discomfort in shoes simply from its bulk.
The white discoloration from nail separation can extend across most of the nail plate. In severe cases, the nail may partially detach or fall off entirely.
Signs the Infection Is Spreading
Most fungal nail infections stay confined to the nail and are more of a cosmetic nuisance than a medical emergency. Bacterial infections carry more risk of spreading. If you notice swelling, warmth, and redness extending beyond the nail fold into the surrounding toe or foot, the infection may be moving into deeper tissue. Additional warning signs include blisters on nearby skin, red streaking up the foot, skin that looks dimpled or pitted, and fever.
People with diabetes, weakened immune systems, or chronic swelling in the legs and feet face a higher risk of nail infections progressing to deeper skin infections. Even athlete’s foot or minor skin cracks can serve as entry points for bacteria. In these cases, what starts as redness around a toenail can escalate into a condition that requires prompt treatment. A rapidly expanding rash with fever warrants urgent attention, while a growing rash without fever should still be evaluated within 24 hours.
Quick Visual Reference
- Yellow or white spots under the nail tip: early fungal infection
- Chalky white patches on the nail surface: superficial fungal infection
- Thick, yellow, crumbling nail with debris underneath: advanced fungal infection
- Red, swollen, warm skin around the cuticle with pus: bacterial paronychia
- Blue-green discoloration on the nail: Pseudomonas bacterial infection
- Black, shiny spot with no nail separation: bruise, not infection
- Redness and swelling spreading beyond the toe: possible deeper tissue infection