As anyone who has ever tried to grow out her hair knows, hair grows slowly. While it does follow a predictable pattern of growth, rest and finally shedding, the process generally takes years. So far, science hasn’t found a way to expedite hair growth to give you long locks overnight, but if you understand the life cycle of your hair, you might be able to estimate how long it will take to grow your hair to your desired length.
Function
Evolution gave all mammals some sort of hair, reports Dr. Thomas Caceci of Virginia Tech. While people have no need of the camouflaging function of animal hair or fur, hair still serves an important purpose for people: insulation. Additionally, like other mammals, humans’ hair provides a way to distinguish between the sexes.
Growth Cycle
Science has identified three stages your hair goes through during its life cycle. This cycle can last as little as two years or as many as seven years, according to Bryn Mawr College. The first stage, called anagen, lasts the longest. The University of Maryland Medical Center reports that on average, a hair will grow in this stage for about 4.5 years, but it could grow for a longer or shorter time. At any given time, the vast majority, about 85 or 90 percent, of individual hairs on your head actively grow in the anagen stage. When a hair stops growing, it has entered the transitional catagen stage, in which it rests. After approximately two to four weeks, the hair will fall out in the telogen phase and a new hair will begin to emerge from the same follicle.
Time Frame
When in the actively growing anagen phase, a hair on your scalp will gain approximately a ½ inch of length per month, according the Ohio State Medical Center. Facial and body hair grows at about half that rate, reports Saint Xavier's University.
Misconceptions
Many people believe hair grows through the skin, as a separate biological material. However, hair is actually part of the skin’s structure, says Dr. Caceci. Just as skin cells go through a process called keratinization to become the tough, insoluble outer layer of the skin, keratinization also creates the keratin proteins that make up the hair shaft. Additionally, the same melanocyte pigments color both your skin and your hair.
Considerations
Although hair grows approximately six inches a year, certain factors can slow down or interrupt the growth cycle. As you age, the hair growth cycle will get shorter and shorter. Additionally, your diet and state of health can affect your hair growth. Hormonal imbalances can trigger strange growth patterns, as well. Some medications and treatments, such as chemotherapy, can cause hair loss, and research suggests any type of extreme stress or trauma can halt hair growth temporarily.
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