Lunula

The Lunula (plural: lunulae), also known as the half-moon, is the crescent-shaped whitish area of the nail bed seen in humans and some other primates. It is the visible part of the nail matrix, also known as the matrix unguis, keratogenous membrane, nail matrix, or onychostroma.

Anatomy

The lunula is the visible part of the nail matrix, the root of the nail that is responsible for producing the nail plate. The lunula is most noticeable on the thumb; however, not everyone's lunula is visible. In humans, it appears by week 14 of gestation, and has a primary structural role in defining the free edge of the distal nail plate.

Function

The lunula's function is to protect the nail matrix from damage, and it also plays a role in the formation of the nail plate. The nail matrix, or the part of the nail bed that is beneath the lunula, produces the majority of the cells that make up the nail plate.

Clinical significance

Changes in the lunula are often a sign of systemic diseases. For example, a smaller lunula can indicate anemia or malnutrition, while a larger lunula can be a sign of cardiovascular disease. The absence of the lunula can be a sign of severe systemic diseases, such as cirrhosis or chronic renal failure.

See also

• Nail anatomy
• Nail disease
• Nail bed
• Nail matrix