Most people are aware of how often they need a haircut and whether they seem to be getting them more frequently than others; but fewer people understand why that's the case or what's behind their rate of hair growth. Lacking such knowledge has caused some to buy into popular myths such as the one that recommends trimming one's hair to stimulate faster hair growth. 

It won't, of course, as hair growth starts at the scalp, not the ends, and no number of haircuts can change that. But experts say it can be helpful to know which factors do determine how frequently you'll be seeing your barber or stylist.

Does fast hair growth mean good health? 

Another myth to put to bed is that fast hair growth is always a sign of better health. It certainly can be since rapid hair growth can sometimes signify that the body has strong cell production for renewing and repairing, but it isn't always so.

Hair grows at an average rate of about half an inch per month (or six inches a year), but some outside factors can contribute to faster growing hair, and they aren't all positive. These include the use of anabolic steroids, taking testosterone or applying topical stimulants such as minoxidil (found in Rogaine) which is often used to treat male pattern baldness. 

"Faster growing hair on the scalp can be a sign of something good, such as pregnancy, which usually causes a surge in estrogen," explains Shari Lipner, MD, an associate professor of clinical dermatology at the Weill Cornell Medical Center. "However," she notes, "a sudden sprouting of hair in other areas of the body may also be the sign of a dangerous condition, such as Cushing syndrome," − a syndrome caused by excess hormones, which can lead to high blood pressure, bone loss or Type 2 diabetes, per Mayo Clinic. 

What causes hair to grow faster than normal? 

Independent of conditions, treatments or performance-enhancing drugs, however, most people's hair grows at different speeds primarily due to heredity. "The rate of hair growth varies from person to person and is mainly influenced by genetics," explains Michelle Henry, MD, a board certified and Harvard trained dermatologist.

This is the case because genes affect the production of hormones connected to hair follicle development, which can affect both hair growth rate and hair density. Research shows that the production of each hair follicle is divided into three stages: anagen (growth), catagen (transition), and telogen (rest). In the anagen phase, hair strands push through one's skin. In the catagen phase, hair stops growing and the follicle shrinks. In the telogen phase, hair falls out so the process can begin again. "The anagen phase of the process is the one most affected by genes," explains Angela Lamb, MD, a dermatologist at Mount Sinai in New York City. Genetics affect one's hair color and texture as well. 

Hair growth rate can also fluctuate with age. "In general, hair grows fastest between 15 and 30 years old and then tends to slow down," says Lipner. 

Does stress affect hair growth? 

Another factor that can impact hair growth is chronic stress, per research published by the National Institutes of Health. Though such connections aren't well understood, it's known that stress increases one's cortisol levels − a hormone that can impact hair follicle development.

Other influences that can determine one's rate of hair growth include "hormonal changes, diet and overall health," says Henry. Foods packed with protein such as chicken breast, fish, greek yogurt and eggs, can help promote healthier hair because hair follicles are mostly made up of protein. Vitamins and minerals such as iron, vitamin A, vitamin B, vitamin E and vitamin D can also make a difference. "Additionally, some medications may also affect hair growth," she adds. 

Many people want thicker hair.Here's how experts say you can get it.