Nutrients such as protein, fat, vitamins, and minerals play important roles in the skin and coat health of cats. Skin and hair are used to prevent things (such as water or heat) from leaving, or things (such as viruses and bacteria) from entering the body.
The hair coat is composed almost entirely of protein. If your cat's diet doesn't contain enough quality protein, her hair may fall out or become dry, weak, and brittle.
Skin is made up of flat cells tightly packed together. These cells have tough membranes that are composed of proteins and fats. Without proper nutrients, cell membranes weaken, allowing water to escape and bacteria and viruses to enter more easily.