Direction of Nail Growth and Thickness

The matrix cells point at an angle toward the cuticle as shown in Figure 2.3. This creates the flat and thin shape of the plate. The length of the matrix determines the thickness of the natural nail plate. Figure 2.4 shows how this occurs. Clearly, the matrix making the longest row of cells will have the tallest stack of cells in the plate. Of course, a real nail plate has thousands of packed cell layers.

Look closely at Figure 2.4 and you will see something else interesting about nail plate growth. This diagram shows that the cells near the back of the matrix have much further to travel before they get to the free edge. The cells coming from the back of the matrix end up on top of the plate. Since they travel further, they must be older than cells below them. At the free edge the surface plate cells are nearly two months older than the cells on the bottom side. This may explain why thin, dry nail plates tend to peel at the top surface, rather than from underneath.