What primarily defines the thickness of the nail plate?

The thickness of the nail plate is primarily influenced by the size of the matrix. The nail matrix is the tissue located under the base of the nail, and it is responsible for producing new cells that become the nail. As the matrix grows and produces more cells, these cells harden and compact to form the nail plate. A larger or more active matrix can lead to a thicker nail plate, as it generates more cells for nail growth.

While the strength of the bed epithelium, the length of the nail bed, and the moisture level of the nail can have various effects on nail health and appearance, they do not primarily dictate the thickness of the nail plate in the same way that the matrix does. The matrix's size and activity directly correlate with how thick or thin the nail plate will be.