Human hair growth
The three stages of hair growth are the anagen, catagen, and telogen phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The rate or speed of hair growth is about 1.25 centimetres or 0.5 inches per month, or about 15 centimetres or 6 inches per year.
Human hair color
Europeans often begin to grow gray hairs in their mid-30s while Asians begin graying in their late 30s, but most Africans retain their original hair color until their mid-40s.