Discolored toenails usually signal something minor, like a fungal infection or a bruise from tight shoes. But the specific color matters. Yellow, white, black, green, and blue toenails each point to different causes, and a few of them deserve prompt attention. Here’s what each color change typically means and what you can do about it.
Yellow Toenails
Yellow is the most common toenail discoloration, and fungal infection is the most frequent cause. Fungal toenail infections thicken the nail, turn it yellow or yellowish-brown, and often make it crumbly at the edges. The infection lives underneath and within the nail plate, which is why it’s stubborn to treat. People who spend time in warm, moist environments (pools, gym showers, sweaty shoes) are especially prone.
Yellow nails can also show up with psoriasis, which causes pitting, thickening, and separation of the nail from the nail bed. Less commonly, yellow nails result from repeated use of dark nail polish without a base coat.
In rare cases, yellow nails that thicken and seem to stop growing entirely can point to yellow nail syndrome, a condition linked to problems with the lymphatic system. Only about 100 cases have been formally reported in medical literature. Around 8 in 10 people with this syndrome develop swelling in the legs from fluid buildup, usually a few months after the nail changes appear. Respiratory symptoms like chronic cough or recurrent lung infections often accompany it. If your yellow nails come with swollen legs or breathing problems, that combination is worth investigating.
White Spots and White Nails
Small white spots on your toenails are extremely common and almost always harmless. The most frequent cause is minor trauma: bumping your toe, wearing shoes that press on your nails, or even an aggressive pedicure. These spots grow out with the nail over several months and don’t need treatment.
White spots can also form on the nail surface from a type of superficial fungal infection, which creates chalky, powdery white patches rather than the small dots caused by trauma. This type responds well to topical treatment since the fungus sits on top of the nail rather than underneath it.
You may have heard that white spots mean you’re low on zinc or calcium. The evidence for this is weak. Researchers remain divided on whether mineral or vitamin deficiencies actually cause white nail spots, and many experts think the connection is overstated.
Nails that are almost entirely white with a dark band at the tip are a different story. This pattern, known as Terry’s nails, can be associated with liver disease, heart failure, kidney disease, or diabetes. It’s more common in older adults and warrants a medical evaluation if you notice it.
Black or Dark Brown Toenails
A dark or black toenail is usually a bruise. Blood pools underneath the nail after trauma, like stubbing your toe, dropping something on it, or running in shoes that are too small. Runners get these so often they call it “runner’s toe.” A bruise under the nail typically appears purple, reddish-black, or dark brown, and it tends to fade at the edges rather than forming a sharp, defined line. As the nail grows out, the discoloration moves forward and eventually disappears.
The concern with dark toenails is melanoma. Subungual melanoma, a skin cancer that develops under the nail, can look like a dark streak running lengthwise from the base of the nail to the tip. Unlike a bruise, this streak doesn’t grow out or fade over weeks. It may widen over time, and the pigment can spread to the skin around the nail (a warning sign called Hutchinson’s sign). A new or changing dark streak on a toenail that you can’t link to an injury should be evaluated by a dermatologist. This is especially important for people with darker skin tones, who have a higher incidence of this type of melanoma.
Green Toenails
A green or blue-green toenail almost always means a bacterial infection, specifically from Pseudomonas aeruginosa. This bacterium thrives in moist environments and produces a pigmented biofilm that stains the nail surface green. People whose hands or feet are frequently wet are most at risk: dishwashers, barbers, nail salon technicians, bakers, janitors, and healthcare workers.
Green nail syndrome typically develops when the nail is already compromised. If you have a nail that’s lifted away from the nail bed, a chronic fungal infection, or ongoing inflammation around the cuticle, bacteria can get underneath and colonize the space. Treatment is straightforward: keep the nails trimmed short, keep them dry, and avoid further trauma. The green color grows out as the nail replaces itself.
Blue or Purple Toenails
Blue toenails indicate your tissues aren’t getting enough oxygen. When blood is well-oxygenated, it’s bright red, giving your skin and nails a pinkish tone. When oxygen levels drop, blood turns darker, and your nails can look blue or purple. The medical term for this is cyanosis.
The most common and least worrying cause is cold exposure. When your feet get cold, blood vessels constrict to preserve core body heat, and your toes may briefly turn blue. This resolves with warming. People with Raynaud’s phenomenon experience an exaggerated version of this, where fingers and toes turn white, then blue, then red in response to cold or stress. Warming and gently massaging the affected areas helps.
Persistent blue nails that don’t improve with warmth can signal circulatory problems or lung conditions that reduce oxygen in your blood. If your toenails stay blue or you notice the color spreading to your skin, that’s a sign your organs may not be getting adequate blood flow and needs prompt evaluation.
Red or Reddish-Brown Lines
Thin, vertical lines of red or reddish-brown under the nail are called splinter hemorrhages because they look like tiny splinters trapped beneath the nail plate. They’re caused by bleeding from small blood vessels in the nail bed.
Trauma is the most common trigger. Stubbing your toe or even getting acrylic nails applied can cause them. Nail psoriasis and lichen planus (a skin condition) also frequently produce these lines; up to 35% of people with lichen planus report splinter hemorrhages.
When splinter hemorrhages appear on multiple nails without any obvious injury, they can indicate something more systemic. Endocarditis, an infection of the heart valves, causes splinter hemorrhages in 15% to 33% of cases. Blood vessel inflammation from autoimmune conditions like lupus can also be responsible. People taking blood thinners are more prone to them as well. A single splinter hemorrhage on one toe after bumping it is nothing to worry about. Multiple unexplained ones across several nails deserve a closer look.
Treating Fungal Toenail Infections
Since fungal infections account for the majority of toenail discoloration, it’s worth understanding what treatment actually looks like. The short answer: it takes a long time, and topical treatments alone often aren’t enough.
Oral antifungal medications are the most effective option. Clinical cure rates for toenail fungus with oral therapy range from about 31% to 76%, depending on the medication. Topical treatments applied directly to the nail are far less effective for toenails, with cure rates as low as 6% to 18%. The nail plate is thick and hard for topical medications to penetrate, which is why pills that attack the fungus through your bloodstream work better.
Even with successful treatment, you won’t see a normal-looking nail for months. Toenails grow slowly, and it takes 12 to 18 months on average for a toenail to fully replace itself. After a fungal infection clears, you’re essentially waiting for the damaged, discolored nail to grow out completely while healthy nail grows in behind it. After trauma, regrowth can take 6 months to 2 years. After a complete nail loss or medical removal, expect up to 18 months for full regrowth.
Signs That Need Medical Attention
Most toenail discoloration is cosmetic or caused by something minor. But certain changes are red flags. A new or changing dark streak running the length of the nail needs a skin cancer check. A nail that lifts away from the nail bed, especially with pain or discharge, needs examination. Redness, swelling, and warmth around the cuticle suggest an infection that can worsen without treatment. Nails that curve dramatically, develop deep horizontal grooves, or become spoon-shaped (dipping down in the middle) can be signs of lung disease, heart disease, or iron deficiency.
Color changes on their own aren’t always dangerous, but they’re your body’s way of signaling that something has changed. When the discoloration doesn’t match an obvious injury, doesn’t grow out over several months, or comes with other symptoms like swelling, pain, or breathing problems, it’s worth getting a professional opinion.