Discolored toenails are most often caused by fungal infections, but the specific color of the discoloration points to very different underlying causes, from minor trauma to serious systemic disease. Understanding what each color signals can help you figure out whether your nail just needs time to grow out or whether something deeper is going on.
Fungal Infections: The Most Common Cause
Fungal nail infections account for the largest share of toenail discoloration worldwide, affecting roughly 5.5% of the general population. That rate climbs steeply with age, reaching as high as 35% in adults over 65. About 90% of fungal toenail infections are caused by a group of fungi called dermatophytes, which thrive in warm, moist environments like the inside of shoes, gym showers, and pool decks.
A fungal infection typically starts as a white or yellowish spot near the tip of the nail. Over time, the nail thickens, becomes brittle, and may develop a crumbly texture along the edges. The discoloration often deepens to a darker yellow or brown as the infection spreads beneath the nail plate. Infected nails can also lift away from the nail bed, creating a gap where debris collects and worsens the appearance.
Diagnosis usually involves scraping a sample from the affected nail to examine under a microscope, sometimes paired with a fungal culture to identify the exact organism. Treatment ranges from topical antifungal solutions for mild cases to oral antifungal medications for more established infections. Because toenails grow slowly (about 1.6 mm per month on average), even after successful treatment it can take 12 to 18 months for a fully clear nail to replace the damaged one.
What Different Colors Can Mean
Yellow Nails
Yellow is the color most people notice first, and fungal infection is by far the leading explanation. But a rare condition called yellow nail syndrome causes all of the nails to turn a thick, yellowish-green with a pronounced curve. This syndrome is linked to problems with lymphatic drainage and lung function. Nearly 2 in 5 people with yellow nail syndrome develop fluid buildup around the lungs, and many experience chronic cough or repeated sinus infections. It has also been reported at higher rates in people with autoimmune diseases, thyroid conditions, rheumatoid arthritis, and certain cancers.
Green Nails
A green or greenish-black toenail usually signals a bacterial infection rather than a fungal one. The bacterium responsible produces blue-green pigments that stain the nail plate. This organism is widespread in soil and water, so people whose hands or feet are frequently wet are at higher risk. The infection is more common in homemakers, dishwashers, bakers, barbers, and healthcare workers. Pre-existing nail damage, chronic exposure to water or detergents, and habits like picking at nails all make infection more likely.
White Spots
Small white spots scattered across one or more nails are extremely common, especially in children. Despite the popular belief that they indicate calcium or iron deficiency, research has found no link between these spots and the mineral content of the nail plate. The cause is almost always minor trauma to the base of the nail, where new nail cells are produced. An overly aggressive pedicure, bumping the toe, or even wearing tight shoes can do it. As the nail grows, the spots simply move forward and eventually disappear off the edge. Zinc deficiency is one of the few nutritional causes that has been validated, but it’s uncommon in people eating a varied diet.
Black or Dark Brown Streaks
A dark streak running lengthwise through the nail can be completely harmless, particularly in people with darker skin tones, where pigmented bands are a normal variant. But a new, widening, or irregular dark band deserves prompt evaluation because it can be a sign of melanoma beneath the nail.
Clinicians use a set of criteria to distinguish between a harmless bruise and potential melanoma. Key warning signs include a band wider than 3 mm with irregular or blurred borders, pigment that spreads onto the surrounding skin fold (known as Hutchinson’s sign), rapid changes in size or color, and involvement of the thumb or big toe (the two most common sites for nail melanoma). A bruise under the nail, by contrast, tends to have a clear history of trauma, may appear broken into separate zones of color, and typically resolves within a few months. Melanoma-related pigment can persist for years.
Trauma and Repetitive Pressure
A single hard impact, like dropping something on your toe, can cause bleeding beneath the nail that shows up as a deep purple, black, or reddish-brown patch. This subungual hematoma is painful at first but usually harmless. If the bleeding is extensive, the nail may eventually loosen and fall off, with a new nail replacing it over the following months.
Repetitive, lower-grade trauma is just as common. Runners, hikers, and anyone who spends long hours on their feet in shoes that are too tight or too short can develop “runner’s toe,” where the nail repeatedly jams against the front of the shoe. This causes bruising, thickening, and discoloration that may affect one or several toenails at once. Wearing properly fitted shoes with a thumb’s width of space between your longest toe and the end of the shoe is the simplest prevention.
Nail Psoriasis
Psoriasis doesn’t just affect the skin. It can target the nails and often does: nail involvement is reported in a significant percentage of people with the condition. The hallmark signs are distinctive. The nail bed may develop yellowish, reddish, or brown patches known as oil drop spots. The nail surface can become pitted with small dents ranging from pinpoint to crayon-tip size, sometimes more than 10 per nail.
As the condition progresses, horizontal grooves may form across the nail, the nail may grow thin enough to crumble, and the thick skin under the nail tip can start to peel away, causing the nail to separate from its bed. That separation then creates a hospitable environment for secondary fungal infection, which complicates both the appearance and the treatment.
Nails That Signal Organ Disease
Certain nail color patterns serve as visible markers of internal disease, particularly affecting the liver, kidneys, or heart.
Terry’s nails appear almost entirely white across the nail bed, with only a narrow pink or brown band (0.5 to 3 mm wide) at the tip. This pattern is frequently associated with liver cirrhosis, chronic heart failure, and adult-onset diabetes. Lindsay’s nails, sometimes called half-and-half nails, show a white proximal half and a reddish-brown distal portion that occupies 20% to 60% of the nail. This pattern is found in up to 40% of people with chronic kidney disease. In both cases, the nail changes reflect altered blood flow and protein levels caused by the underlying organ dysfunction, not a problem with the nail itself.
How Long Discoloration Takes to Clear
Toenails grow at an average rate of about 1.6 mm per month, which is less than half the speed of fingernails. The big toenail grows fastest among the toes but still takes roughly 12 to 18 months to fully replace itself. That means even after you’ve addressed the underlying cause, whether it’s treating a fungal infection, waiting for a bruise to grow out, or managing psoriasis, visible improvement is slow. Younger people and men tend to have slightly faster nail growth, but the differences are modest.
If a discolored nail hasn’t improved after several months of treatment, or if the discoloration is spreading rather than growing out, that’s a signal the original diagnosis may need revisiting. A nail that fails to improve despite adequate treatment is itself considered a warning sign worth investigating further.