Nails are made of a protein called keratin. It is the same protein that makes up hair and skin. Nails are porous, but they do not have oil glands or sweat glands. This means that nails rely on water for hydration.   The nail plate is made up of layers, each with different functions:   Outer layer: The cuticle, which covers the nail bed and protects it from bacteria.   Middle layer: The lunula (the half moon at the base of the nail), which provides a natural buffer against wear and tear.   Inner layer: The matrix (the area under the cuticle), which produces new cells to replace old ones as they wear away.   The matrix is important in nail growth and repair. Nails grow 10-25 cells a day, like hair, skin, and bone. Vitamin C deficiency can result in brittle nails that crack easily or even fall off.