What is the Lunula (Half-Moon White Part of the Nail)?
The lunula is the visible portion of the distal nail matrix that extends beyond the proximal nail fold, appearing as a white, half-moon-shaped area at the base of your fingernails and toenails. 1
Normal Anatomy and Function
The lunula appears by week 14 of gestation and has unique histologic features that distinguish it from other parts of the nail unit 1
It serves a primary structural role in defining the free edge of the distal nail plate, making it functionally important for normal nail architecture 1
The white color results from the underlying nail matrix tissue being visible through the transparent nail plate, and this is the only portion of the nail matrix that can be directly visualized 2, 3
Clinical Significance of Lunula Changes
Size Variations
Macrolunula (enlarged lunula) can indicate local trauma, systemic disorders including hyperthyroidism, ischemia, leprosy, and scleroderma, or congenital conditions 4
Microlunula or anolunula (small or absent lunula) can be a normal variant but may also indicate systemic disease, particularly in HIV infection where total anolunula (absence in all fingernails) correlates directly with disease stage progression 5
Color Changes
Red lunula results from increased density of dilated vascular channels in the superficial papillary dermis of the nail matrix, which can be associated with inflammatory conditions like lichen planus or systemic disorders 2, 3
Red lunula can present as complete (entire lunula is red), incomplete (only proximal portion is red), or mottled forms 2
When to Be Concerned
Involvement of the lunula in fungal infections indicates more extensive disease requiring systemic rather than topical antifungal therapy alone 6
Changes in lunula morphology or color can indicate either cutaneous or systemic disorders and warrant further evaluation 1
In HIV-positive patients, progressive loss of lunula visibility correlates with advancing disease stage and may serve as a clinical marker 5