|Gray's||subject #234 1066|
It appears by week 14 of gestation, and has a primary structural role in defining the free edge of the distal nail plate (the part of the nail that actually grows outward).
It is located at the end of the nail that is closest to the skin of the finger but still lies under the nail. It is not actually white but only appears so when seen through the nail.
It is half-moon-shaped, and has unique histologic features.
The lunula is most noticeable on the thumb, and not everyone's lunula is visible.
The lunula and the nail itself are good places to find warning signs of certain diseases such as liver disease, kidney disease, heart problems, and lung diseases. Any color differences or unusual lines may indicate some type of disease or insufficiency. However, vertical lines on one's fingernails are normal as one ages.
Lunular anomalies include changes in form, structure or color. Lunular dysmorphologic features (that is, anomalies in form) can be characterized by macrolunula, microlunula or anolunula, and nonconvex lunula. Lunular dyschromias (color anomalies) can be confluent or spotted or can be characterized by longitudinal colored bands that traverse the lunula. Alterations in the morphologic features or color (or both) of the lunula can be an indication of either a cutaneous or a systemic disorder.