What causes white spots on fingernails?

White Spots on Fingernails: Causes and Clinical Significance

White spots on fingernails are most commonly caused by minor trauma to the nail matrix, but can also indicate fungal infections (superficial white onychomycosis), systemic diseases, or hereditary conditions depending on their pattern and distribution. 1, 2

Diagnostic Approach Based on Pattern

The key to diagnosis is distinguishing between true leukonychia (abnormality in the nail plate itself), apparent leukonychia (nail bed changes), and pseudoleukonychia (surface-only changes). 2

Most Common Cause: Traumatic True Leukonychia

• Small white spots or lines that grow out with the nail are typically caused by minor trauma to the nail matrix during nail formation 1
• These are benign, require no treatment, and resolve as the nail grows out over 6-8 months 1
• This is the most frequent presentation in otherwise healthy individuals 2

Fungal Infection: Superficial White Onychomycosis (SWO)

If white spots are crumbling, spreading, or involve the nail surface:

• SWO begins at the superficial layer of the nail plate and spreads to deeper layers, appearing as crumbling white lesions 3
• This condition is most commonly seen in children and is usually caused by T. interdigitale infection 3
• Confirmation requires direct microscopy with potassium hydroxide preparation and fungal culture on Sabouraud's glucose agar 4
• Treatment with antifungal agents is indicated if fungal infection is confirmed 4

Systemic Disease Indicators

Transverse white bands (Mees' lines or Muehrcke's lines):

• Can indicate systemic illness, toxin exposure, or medications 5
• Have been documented following acute systemic infections including tuberculosis and bacterial empyema 5
• Require evaluation for underlying systemic disease 2

Total or subtotal white discoloration:

• May indicate serious conditions like liver failure (Terry's nails) or kidney failure (Lindsay's nails) 2
• Hereditary leukonychia totalis presents as complete white discoloration from birth, typically inherited in autosomal dominant pattern 6

Key Differentiating Features

Examine these specific characteristics:

• Location: Fingernails vs. toenails (fungal infections more commonly affect toenails) 3
• Texture: Smooth vs. crumbling (crumbling suggests fungal infection) 3
• Growth pattern: Does it move distally with nail growth (trauma) or remain fixed (apparent leukonychia from nail bed) 2
• Distribution: Single nail, multiple nails, or all nails 2
• Associated findings: Nail thickening, separation from nail bed, or periungual inflammation 3, 4

Common Pitfalls to Avoid

• Do not assume all white spots are benign trauma - always assess for spreading, crumbling texture, or systemic symptoms 3, 2
• Do not treat presumed fungal infections without mycological confirmation - many nail conditions mimic onychomycosis 4
• Consider occupational exposure - chronic moisture exposure in healthcare workers, homemakers, or plumbers increases risk of both fungal and bacterial (Pseudomonas) nail infections 4, 7

When to Investigate Further

Obtain mycological studies if:

• White discoloration is spreading, crumbling, or involves nail surface 3
• Multiple nails are affected without clear trauma history 4
• Patient has risk factors: diabetes, immunosuppression, peripheral vascular disease, or HIV infection 3

Consider systemic workup if:

• Transverse white bands appear suddenly without trauma 5
• Total or near-total white discoloration is present 2
• Associated systemic symptoms are present 5