You were right in referring to it as a “moon” . but it name as..
- Lunula of Fingernail
The lunula of a fingernail is the whitish or paler hemispheric portion of the nail body arcing upwards from the cuticle or eponychium. It has the appearance of a half-moon. Lunula is Latin for “moon”. All the nails have lunulae, however, the lunula’s appearance is most marked in the thumb; and on the other nails the lunula may not be visible at all, hidden beneath the cuticle and the skin further back along the phalanges. The cells of the lunula are the same keratinized cells that make up the rest of the nail bed, but they are slightly less developed than the other cells and less firmly attached to the nail bed, resulting in its lighter appearance.
The white crescent at the proximal end is called the lunula. It is white because the underlying epithelium is thicker here, and the color of the dermis does not show through from underneath.
The epithelium underlying the nail bed and nail plate, forms a continuous fold, first forming the cuticle or eponychium(epo=above) at the proximal end of the nail, overlying the nail plate, then the nail bed underneath the nail plate and finally the hyponychium (hypo=below); a thickened region of stratum corneum that secures the nail to the fingertip, and lies below the nail plate.
- Cuticle (Eponychium) of Fingernail
The cuticle or eponychium of the fingernail is a specialized form of epidermis that is found over the base of the nails of the fingers. It is a thin layer of skin that covers the nail plate and nail root just before the nail emerges at the surface, where the keratinized cells will be completely developed. However, the cuticle is not made up of cells but is rather a secretion of the epidermal cells, coating the end of the skin on top of the nail body. It brings the skin on the finger and the nail plate together to provide a barrier that’s waterproof. Beneath the eponychium is the membranous pterygium, providing further protection to the skin against bacteria and infection. The eponychium folds over the top of and back in on the lower edge of the epidermal cells at the junction with the nail. Just beyond the cuticle, particularly on the thumb, the nail body may be whitish or lighter in color in a small hemisphere called a lunula.
There are various web sources that claim a non-visible lunula is predictive of some or another type of disease, this is very misleading as hidden or non-visible lunula are more of a genetic disposition than anything. Those that claim that rely on a cause and effect reasoning which simply doesn’t hold water
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