White spots on nails, known in medical circles as leukonychia, can occur from a variety of factors, but are most likely the result of injury. Below we set out some of the most common leukonychia causes.
Injury or trauma to the matrix
Injury or trauma to the nail matrix (see nail anatomy diagram below) is the most common cause of white marks on fingernails or toenails. The matrix is the root of the nail where new keratin cells that make up the nail are incubated and formed. These new keratin cells are originally white in color but as more are produced, the older cells are pushed forwards and flattened, losing their white appearance. If trauma occurs to the nail matrix this keratinazation process can be defective (essentially the nail cells do not flatten) resulting in leukonychia puncata (white spots on the nails).
In most cases it will be hard to link the appearance of the white spot to a particular injury event (such as slamming your fingernail in a car door for example) as it can take 6 weeks before it appears from under the eponychium. Injury to the matrix may result from a manicure that puts excessive pressure on the area. Picking and biting of the nails may also be the cause. Leukonychia spots generally grow out – but as nails are slow growing this process can take several months.
The location of the eponychium and nail matrix are labeled in the diagram below.
Reaction to nail products
White spots on nails can occur as a reaction to nail polish or nail hardeners (especially products containing acetone or formaldehyde). The reaction can either be an allergic one or the white spots may result from the loss of oil and moisture from excessive solvent use. People with thinner nails are more susceptible to moisture loss. Applying a moisturizer to the nail plate and cuticle area is generally effective at removing any white marks on nails fairly quickly. The condition is referred to as pseudo leukonychia and is typically temporary.
Nail fungus infections
We have an entire section of this website dealing with nail fungus or Onychomycosis. The infection is caused by a dermatophyte fungus that invades the keratin of the nail (in rare cases molds or yeasts can be involved). In its most common form – known as Distal lateral Subungal Onychomycosis – the discoloration spreads from the tip of the nail (the distal edge) towards the cuticle and proximal fold. While normally a yellowish tinge is present, it can also appear as a whitish or opaque discoloration. A less common form of nail fungus, known as White Superficial Onychomycosos – can result in spreading opaque patches and white nails. Texture changes such as brittleness and crumbing are typically also apparent. See more on nail fungus treatment. Nail fungus infections can occur on both toenails and fingernails, although the former is much more likely.
Liver or kidney problems
Leukonychia totalis, where the entire nail plate turns white, can be the result of kidney or liver failure. But in most cases, there will also be other symptoms. Leukonychia striata is characterized by white lines running parallel to the lanula reaching completely across the nail, and occurring in more than one nail. This may be caused by a chronic liver disease, chemotherapy or heavy metal positing.
In the past white spots on fingernails and toenails were often associated with a zinc or calcium deficiency, but this is now thought to be an unlikely cause in most cases.