What part of the nail protects the nail bed from bacterial invasion?

The hyponychium serves as a protective barrier for the nail bed against bacterial invasion. Located beneath the free edge of the nail, it is the area of skin that connects the nail plate to the fingertip. This structure helps to seal the area and prevent pathogens from entering, thereby providing an important defense mechanism for the underlying tissues of the nail bed.

The other options, while related to nail anatomy, serve different functions. The eponychium, often confused with the cuticle, is the tissue that overlaps the proximal end of the nail plate but does not primarily protect the nail bed from infections. The lunula, which is the visible part of the nail matrix at the base of the nail plate, does not function as a barrier against bacteria. The cuticle, while offering some protection, mainly serves to seal the area between the skin and the nail plate but is not as effective as the hyponychium in guarding the nail bed specifically from bacterial invasion.