The lunula is the pale, half-moon shaped arc at the base of the nail that marks the far end of the germinal matrix, where the new nail plate is still being formed.
Also known as: half moon, half-moon of the nail, lunulae, nail moon
The lunula is the crescent at the base of the nail, most visible on the thumbs. It is the part of the nail matrix that extends beyond the proximal nail fold, seen through the plate. It looks whiter than the rest of the nail because the plate above it is still being formed and the matrix beneath is thicker, so the pink of the nail bed shows less (Medscape).
The size of the lunula varies from person to person and from finger to finger. It is largest on the thumb and often hidden under the fold on the little finger. A lunula that cannot be seen is common and usually means the fold covers it. Its curve often matches the curve of the natural free edge on the same finger.
The lunula is soft, living tissue under a thin plate. Pressing hard on it with a cuticle pusher, or filing over it, can bruise the matrix beneath and leave a white spot or ridge in the nail that grows out over months. Cuticle work stops at the edge of the fold.
In nail design, the lunula is a reference point. A half-moon manicure leaves it bare, or paints it in a contrast colour. In a reverse French the curve of colour follows the curve of the lunula. Changes that appear on all nails at once, such as a colour change across the plate, are a reason to see a GP (Mayo Clinic).