Our hair and nails are made up of almost identical cells. There are basically 3 types of cells in our hair - cuticle , cortex and medulla. The cuticle is responsible for different hair colors. And the medulla is responsible for hair growth. Melanin is responsible for the different colors of our skin. Melanin is also responsible for the different colors of our hair. Hair color is either black or gray if the cuticle contains eumelanin. And if there is pheomelanin, it is red. And if the melanin is low, the color is golden. There are several steps to growing hair. The first stage is called anagen , the second stage is called categen , and the last stage is called telogen. The cells of our body continue to divide , that is, one cell breaks into two , two breaks into four , and so on. And our body continues to grow. As you grow older , the rate at which these cells break down decreases. And the hair grows in the same way. This growth rate is higher in the anagen stage. A hair can stay in this stage for 2 to 6 years. During this time the hair grows not only on the top , but also on the roots of the hair. At this stage, the more the roots of the hair grow , the bigger the hair becomes. Then comes the catechin stage of hair.