White marks on toenails, medically known as leukonychia, are a common concern. This discoloration is a general term for various changes in the nail plate, the hard, visible part of the nail. While they can look alarming, these marks usually indicate one of two main issues: a physical injury or a fungal infection. Understanding the difference between these causes is the first step toward finding the correct course of action.
Non-Infectious Causes of Discoloration
The most frequent reason for white marks is minor trauma, a non-infectious condition called true leukonychia. This occurs when the nail matrix, the area where the nail plate is formed, is damaged. The injury causes a defect in the keratinization process, trapping tiny pockets of air within the new nail tissue that appear white as the nail grows out.
This damage can manifest as leukonychia punctata (small, scattered white spots) or leukonychia striata (horizontal white lines). Repetitive, low-level impacts, such as constant rubbing from tight shoes or damage from an aggressive pedicure, are often the culprits. These trauma-induced marks are harmless and will simply grow out with the nail, a process that can take 12 to 18 months due to slow toenail growth.
While trauma is the most likely cause, white nails can rarely signal a systemic issue. Severe nutritional deficiencies, like a lack of zinc, or certain health conditions may cause nail discoloration. However, if no other symptoms are present, the white spots are highly probable results of a forgotten bump or repeated pressure.
White Marks Caused by Fungal Infection
A different and more concerning source of white discoloration is a fungal infection, medically termed onychomycosis. The white marks are caused by fungi consuming the nail’s keratin, not by trauma. The specific type most likely to cause surface white marks is Superficial White Onychomycosis (SWO), which is less common than other forms of nail fungus.
SWO begins with small, well-defined white patches on the top layer of the nail that may look powdery or chalky. Unlike trauma marks, which are embedded and grow out, these fungal spots can often be scraped off the nail surface. As the infection progresses, the white areas may spread, causing the nail surface to become rough, soft, and brittle.
Fungi thrive in warm, moist environments, making shoes and socks an ideal breeding ground. The organism responsible for SWO often invades the nail directly from the surface. If the white marks are spreading, changing the nail’s texture, or have a dusty, powdery appearance, a fungal cause is more probable than a simple injury.
Treatment and Prevention Strategies
The action taken to resolve white marks depends entirely on the cause, making correct identification important. For marks caused by trauma, no specific treatment is necessary, as the discolored section will eventually be clipped away as the nail grows out. The best approach is preventing new marks by ensuring footwear fits correctly, especially athletic shoes, to avoid repetitive stress.
If a fungal infection like SWO is suspected, over-the-counter antifungal creams may be tried, sometimes requiring the nail to be filed down first. Prescription-strength oral or topical antifungal medications are often the most effective treatment, especially for spreading infections. Because toenails grow slowly, any treatment requires patience, often taking six to nine months to show full results.
Consult a podiatrist or dermatologist if the white marks cover a large portion of the nail, are spreading quickly, or if the nail is becoming thick, crumbly, or painful. General prevention strategies include maintaining proper foot hygiene, keeping the feet dry, and wearing moisture-wicking socks. Avoiding harsh chemicals like acetone-based polish removers can also help maintain the nail’s integrity.