Toenail discoloration is most often caused by a fungal infection, which accounts for up to 50% of all nail diseases worldwide. But color changes in your toenails can also signal trauma, bacterial infections, skin conditions, medication side effects, or occasionally something happening deeper inside your body. The specific color your nail turns is a useful clue to what’s going on.
Fungal Infections
Fungal nail infections (onychomycosis) affect roughly 10% of the general population and nearly 20% of people over age 60. They’re by far the most common reason toenails change color. The hallmark is a white-yellow discoloration, usually starting at the tip or side of the nail and working its way back. Over time, the nail thickens, becomes brittle, and collects chalky debris underneath.
Not all fungal infections look the same. The most common type starts at the free edge of the nail and spreads inward, turning it yellow-white. But fungal infections can also produce brown, orange, or even black discoloration depending on the type of fungus and how deep the infection goes. One variant causes white patches or streaks across the surface of the nail. Another starts near the cuticle and creates a white spot that expands outward. If you notice your toenail gradually yellowing and thickening, especially if more than one nail is affected, a fungal infection is the most likely explanation.
Trauma and Bruising
Stubbing your toe, dropping something on your foot, or wearing shoes that are too tight can all cause bleeding underneath the nail. This trapped blood, called a subungual hematoma, initially looks red or purple, then gradually darkens to brown or black as the blood breaks down. It can look alarming, but it’s essentially a bruise.
The discoloration grows out with the nail, which takes six to nine months for a toenail to fully replace itself. Runners and hikers are especially prone to this type of discoloration because of repetitive pressure against the front of the shoe. The key distinction from something more serious: a bruise stays the same size relative to the nail and slowly moves toward the tip as the nail grows. A dark streak that doesn’t move or that changes over time is a different situation entirely.
Bacterial Infections
A blue-green or greenish-black toenail usually points to a bacterial infection, specifically Pseudomonas aeruginosa. This bacterium produces a colored biofilm on the nail surface, giving it a distinctive green tint that’s hard to miss. It thrives in moist environments, which is why green nail syndrome is more common in people whose feet stay wet for extended periods or who already have a damaged nail from a fungal infection or prior injury.
People who work in wet conditions (dishwashers, janitors, medical personnel) are at higher risk. Artificial nails and nail products may also create the kind of warm, sealed environment that encourages bacterial growth, though the evidence on that is limited.
Psoriasis and Skin Conditions
Psoriasis doesn’t just affect your skin. Between 10% and 55% of people with psoriasis develop nail changes, including a distinctive discoloration called the “oil drop sign.” This appears as a translucent yellow-red patch under the nail that looks exactly like a drop of oil trapped beneath the nail plate. It’s considered the most diagnostic visual marker of nail psoriasis.
Psoriasis can also cause tiny pits in the nail surface that look like they were made with an icepick, along with thickening and crumbling of the nail edge. If you already have psoriasis on your skin or scalp and notice these nail changes, the two are almost certainly connected. In fewer than 5% of cases, nail psoriasis shows up without any skin involvement at all.
Medications That Change Nail Color
Certain medications can trigger pigment changes in your toenails by activating the pigment-producing cells in the nail root. Chemotherapy drugs are the most well-known culprits, particularly those used to treat cancer such as anthracyclines and fluoropyrimidines. The nails may develop brown-to-black longitudinal bands (a single dark stripe running from base to tip) or become darkened across the entire nail plate.
The discoloration typically appears weeks into treatment and can affect one nail or many. It’s not dangerous on its own, but it can be distressing. In most cases, the color gradually grows out after the medication is stopped. Even some topical preparations, including certain antifungal creams, have been reported to turn nails yellow.
What Nail Color Can Reveal About Your Health
Sometimes toenail discoloration has nothing to do with the nail itself. It reflects something happening in the rest of your body. Specific patterns have well-established links to internal conditions:
- Mostly white nails with a small pink band at the tip (Terry’s nails): Originally described in patients with severe liver disease, where 80% of cirrhosis patients had this finding. It’s caused by decreased blood flow and increased connective tissue in the nail bed. It can also appear with diabetes, heart failure, and aging.
- Pairs of white horizontal lines (Muehrcke’s lines): These appear when blood protein levels drop significantly and are associated with kidney disease, liver disease, and malnutrition. They disappear when protein levels return to normal, which confirms they originate in the nail bed rather than the nail plate itself.
- Half pink, half white nails: A pattern linked to kidney disease.
- Pale nails: Can indicate anemia.
- Blue nails: Suggest low oxygen levels in the blood.
- Spoon-shaped nails that dip in the middle: Often a sign of iron deficiency.
Yellow nail syndrome is an extremely rare condition (fewer than one in a million people) in which the nails turn yellow, thicken, and nearly stop growing. It’s diagnosed when at least two features of a clinical triad are present: yellow nails, swelling in the limbs from fluid buildup, and respiratory problems like chronic cough or recurrent lung infections.
Dark Streaks and Melanoma
A new or changing dark streak running the length of a toenail deserves prompt attention. Subungual melanoma, a type of skin cancer that develops under the nail, can appear as a brown-to-black band, typically 3 mm or wider, with irregular or blurred borders. It may also cause pigment to spread onto the surrounding skin near the cuticle.
This is uncommon, but it’s the one form of toenail discoloration where timing matters. A bruise grows out. A melanoma doesn’t. If you have a dark stripe that stays in place, gets wider, or has uneven color, that distinction is critical. People with darker skin tones develop subungual melanoma at higher rates relative to other types of melanoma, so awareness is especially important.
Sorting Out the Cause
Color alone narrows the possibilities considerably. Yellow-white and thickening points toward fungus. Green means bacteria. A dark spot that’s growing out is likely a bruise. A dark streak that isn’t moving could be medication-related, normal pigmentation (common in people with darker skin), or rarely melanoma. White nails across multiple fingers and toes suggest a systemic issue worth investigating.
A few features warrant a closer look from a dermatologist: any new dark streak, a nail that’s lifting away from the bed without an obvious cause, redness and swelling around the nail, nails that seem to stop growing entirely, or deep horizontal grooves that run across the width of the nail (which indicate your nail growth was temporarily interrupted by illness or stress). Most toenail discoloration turns out to be fungal or traumatic, both of which are manageable, but getting the right diagnosis first saves you from months of treating the wrong thing.