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What controls hair growth?

vcruz's picture

      For many people, the hair is considered to be an important part of their physical appearance and dedicate a lot of their time and energy to their hair maintenance and care. There are more and more products developed to improve the growth and prevent the loss of hair in men as well as in women. However, we rarely see any of these products to really prove to work. Many women frustrate over the fact that they cannot grow their hair past a certain length, while other women do not even need to put any efforts for growing beautiful long hair; and at a certain age, men start worrying about the signs of hair loss, while others grow old without this problem. This makes one wonder, what is it that causes some people to be able to grow beautiful, long, strong hair, while others do not. Is this simply established in our genes and thus controlled in our brain, or does this depend on certain behaviors, treatments, experiences, etc .that we may have exposed our hair to throughout our life? Is this simply controlled by our brain? Or is it a combination of many of these?

     In our Neurobiology and Behavior class, we have learned about the ways in which many parts of our body are controlled by our nervous system, even those components that we would not even think of as being related to the nervous system. In one class, we discussed how certain things, like body heat and our “normal” weight are some of those features that are “controlled” by what can be seen as a “thermostat” that operates within our nervous system and that allows for these different factors to return to its “normal” state whenever they have reached an “abnormal” state [1].  Studies suggest that this theory can also be applied to the ways in which our hair grows.

      In The World of Hair, an on-line reference, Dr. John Gray presents an explanation for the ways in which hair grows differently in all people. According to Dr. Gray, the main justification for the ways in which hair grows is found in the hair cycle, which according to him, it is necessary “to know about in order to understand many of the problems people have with their hair”[1]. The hair cycle is composed of three stages: anagen, catagen, and telogen. Each particular phase determines how the hair will grow in each individual. 

     The first phase, Anagen is the “growing phase” in which new hair starts to grow. Studies suggest that this phase lasts anywhere from two to seven years [1, 2]. It is estimated that, “Approximately 85% of all hairs are at the growing phase in any one time” [2]. The length of this stage in each individual determines how long or short that person is capable of growing his or her hair since “Hair grows approximately 10cm per year” [2]. Thus, depending on how long anagen lasts in a person, that determines how long that person’s hair will grow. In a way, this serves like the “thermostat” that regulates the “normal” temperature, even if a person opts to not cut his or her hair for many years, depending on how long anagen lasts, that person’s hair cannot pass a certain length (though unlike the thermostat, anagen cannot do anything to “regulate” how short someone wishes to have his or her hair). 

     Catagen, the second phase, is “a “short resting phase” which lasts from two to four weeks in the human scalp and there is no pigment made during that time [1]. Unlike Anagen, during this phase the follicle[1] stops producing hair, and “the base of the follicle moves upwards towards the surface of the skin” [1]. Finally, Telogen lasts for three or four months and it is during this phase that the hair falls and “new hair begins to grow from the hair follicle” [1]. Although this is the phase that causes many people to constantly worry, as their hair falls as they brush it or just run their hands through it, this is very normal as Dr. Gray explains that “at any one time, around one in ten of the follicles on an individual’s head are in the shedding phase” [1]. Yet, studies also suggest that other factors also cause hair to fall out aside from those that naturally would fall due to the hair cycle.

     Many people believe stress to be a significant cause of hair problems, such as hair loss. However, debates exist about these types of beliefs. For example, a study made by the Department of International Medicine in Humboldt University suggests that stress, rather than being a cause for hair loss, “may indeed inhibit hair growth” [3]. Less debated theories argue that a good nutrition and great intakes of water improves the condition of the hair [4]. While all of these theories have not been proven to be true for all people, it can be argued that the ways in which our hair grows is not only caused by the way in which one part of our brain has determined it to be. From experience we may know that somehow, the way in which we treat our hair can really affect its growth and overall condition; however, when it comes to growing our hair a significantly long, many of us might find it impossible to get it past a certain length as a result of the length of our anagen phase. Still, I wonder if, in the same way that one’s body temperature is readjusted in cases like when we have a fever, could there be an alteration in our cycle that could allow our hair growth to be longer than it is already established to be? If this was possible, it would solve may people’s desire to grow beautiful long hair in the same way that scientists have already come up with products that prevent significant hair loss.

[1] Dr. Gray describes the follicle as a “tiny but powerful factory, which throughout many people’s lifetime hardly ever stops working”; it is the place where the hair is produced, and grows until it falls out during telogen.




[1] Hair Structure and Hair Life Cycle. Accessed April 7th, 2009

[2]Dr. John Gray, The World of Hair, an on-line reference provided by the P&H Hair Care Research Center, 

[3] Arch, et al. “Indicators for a ‘brain-hair follicle axis (BHA)’: inhibition of keratonycyte proliferation and upregulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P1” The FASEB Journal, November 2001, Germany

[4] Karen Marie Shelton, “Hair Vitamins: Water & Hair Growth,”



Ambreen Nisa's picture

Hair Growth

Its my first visit to your blog and i have found it so useful and informative
specially this post.I think diet and stress are the two main parts for hair growth. If anyone take good diet and never take stress, then he must have strong hair.

intrigued inquirer 's picture

Hair growth and loss

I believe that untroubled hair will grow longer then 10cm per year as mine does.

I do believe stress does assist with hair loss and male pattern baldness but lack of nutrition play a big part. Yet at the same time stress does assist in the growth of hair but in different areas of the body

Paul Grobstein's picture

hair growth, the brain, and ...

My guess is that while hair growth can be influenced by the brain and behavior there are also influences on it independent of both.  If I remember correctly, hair growth often persists for some period after people die (ie no longer have any observable brain function).   
bina paul's picture


How is it possible for hair to keep growing after death?

Serendip Visitor's picture

hair growth after death

hair continuing to grow after death is actually a myth. what is actually happening is that the skin, muscle, and other tissues shrink, while the hair remains the same length, forcing the hair outward and making the it appear longer.

siva123's picture

For Male Pattern Baldness,

For Male Pattern Baldness, the better treatment is hair replacement surgery. hair transplant is a good method for hair restoration. With Quality surgeons and better technicians, your hair loss treatment provides a guaranteed results