Hair grows on average 4-7 inches per year. For those wanting to grow their hair long, this can make for a long wait. A variety of factors determine how fast the hair grows including age, gender, hormone levels, diet, and physical health.
Hair that is damaged will grow slower than normal, healthy hair. Why? Growth is slowed not only because of the hair damage itself, but because of the health of the scalp. Those who color, process, heat style and otherwise abuse the hair regularly also tend to damage the scalp, leading to poor circulation, clogged pores and therefore reduced growth.