White toenails, medically known as leukonychia, represent a change in the nail plate that causes it to lose its natural translucent pink appearance and look white. This discoloration can manifest in various ways, ranging from small, scattered white spots or lines across the nail, to the entire nail turning opaque white. The underlying causes are diverse, spanning from minor external factors to persistent infections or, rarely, indicators of internal health issues.
External and Cosmetic Factors
The most frequent causes of white toenails relate to physical stress or cosmetic practices affecting the nail plate. Minor trauma to the nail matrix, the area where the nail grows, can result in small white spots or lines known as punctate or striate leukonychia. This damage is commonly caused by ill-fitting footwear that repeatedly presses on the toes or by minor injuries like stubbing a toe. These white marks are small pockets of air trapped within the nail layers and will simply grow out with the nail over several months.
Another common cosmetic cause is keratin granulation, a superficial whiteness that appears after removing dark nail polish. This occurs because the polish or harsh removers like acetone dehydrate the superficial layers of the nail plate. The result is a chalky, rough, and uneven white patch on the nail surface, which is harmless and temporary. Allowing the nail to breathe between polish applications can help prevent this dehydration.
The Role of Fungal Infection
Fungal infection, or onychomycosis, is a prevalent medical cause of white toenails, especially in adults. One specific type is superficial white onychomycosis (SWO), characterized by white patches that begin on the top layer of the nail plate. These spots often look powdery or chalky and can spread across the entire surface, causing the nail to become soft and crumble. SWO is caused by fungi, typically dermatophytes, that invade the superficial keratin layers.
A more common form of fungal infection, distal subungual onychomycosis, can also cause a white appearance, though it usually starts at the nail’s edge and moves inward. This infection occurs beneath the nail plate, leading to a buildup of keratin debris that appears white or yellowish and causes the nail to thicken and lift from the nail bed. Fungal infections are contagious and thrive in warm, moist environments like sweaty shoes, requiring specific antifungal treatment to resolve.
White Nails as Systemic Health Indicators
While most white nail changes are local, certain patterns, known as apparent leukonychia, can signal underlying systemic health conditions. One distinct pattern is Terry’s Nails, where nearly the entire nail plate appears opaque white, but a narrow, pink band remains at the tip. This appearance is due to a change in the nail bed’s vascularity, and it is associated with conditions like liver cirrhosis, chronic kidney disease, and congestive heart failure.
Another specific presentation is Muehrcke’s Lines, which appear as paired, horizontal white lines parallel to the base of the nail. Unlike lines caused by trauma, these lines are in the nail bed and do not move as the nail grows out. Muehrcke’s Lines are often linked to low protein levels in the blood (hypoalbuminemia), which can be a sign of kidney disease or malnutrition. Total leukonychia, where the entire nail is uniformly white, is a rare presentation that can be genetic or acquired due to systemic illness.
Diagnosis and Treatment Options
A persistent or spreading white discoloration warrants consultation with a healthcare professional, such as a podiatrist or dermatologist, especially if accompanied by pain, thickening, or crumbling. The diagnostic process typically involves a physical examination and may include taking a sample of the nail or debris for laboratory testing to confirm or rule out a fungal infection. This testing is important because other conditions, like psoriasis, can mimic the appearance of a fungal infection.
Treatment is entirely dependent on the identified cause. Fungal infections often require long-term commitment; mild cases may respond to prescription-strength topical antifungal solutions or medicated nail polish applied daily for several months. More severe infections often necessitate oral antifungal medications, which are effective but require monitoring for potential side effects. For white nails caused by trauma or cosmetic factors, the only treatment is time, as the nail must grow out completely, a process that can take six to nine months for a toenail. Prevention involves wearing properly fitted shoes to avoid micro-trauma and maintaining good foot hygiene.