Example of a normal lunula in a female thumb.

The lunula, or lunulae (a.k.a. the ‘nail moon’), is the crescent-shaped whitish area of the bed of a fingernail (or toenail). The lunula can also be described as the visible part of the nail matrix – which is the ‘root’ of the nail.

The lunula or the white ‘half moon’ at the base or proximal end of the fingernail is particularly smooth, flat and shiny. The whiteness of the lunula is still a matter of controversy but its absence – especialy when the lunula is not present in the first finger (thumb) – could be described as notable and important.

In certain chromosome abnormalities the lunula is absent, i.e., monosomia 4 and the lunulae may be diminished in trisomy 21 (= Down syndrome).

A technical description of the ‘lunuala’ from An Atlas of DISEASES OF THE NAIL:

“…the matrix is responsible for the majority of the nail plate substance. The proximal portion of the matrix lies beneath the nail folds and the distal curved edge can usually be seen through the nail plate as the white lunula.”

Example of a normal lunula in a male thumb.