Which vitamin deficiency causes hair loss?

The science of hair 

Hair is more than just an aesthetic part of our bodies. Indeed, hair helps to transmit sensory information and plays a major role in people’s identities. Interestingly, all of our hair follicles are formed in the womb before we are born. In fact, by week 22 of pregnancy, a foetus already has all of its hair follicles. Many of us take our hair for granted until we experience hair loss, in fact there are numerous products and supplements advertised for hair growth. But what really causes hair loss, is there a vitamin deficiency that causes hair loss or something else? Let's start by looking at the science of hair. 

Our scalp contains approximately one hundred thousand hair follicles which is the highest number of follicles a human can have throughout their lifetime. In fact, we cannot generate new hair follicles beyond those we are born with. If you’ve ever wondered why your hair density seems lower as an adult compared to when you were a child, this is because our scalps grow as we transition from childhood to adulthood. 

Moreover, hair contains two different structures: the follicle and the shaft. The former is located in the skin whereas the latter is externally visible on the scalp. Our hair grows at a rate of about 6 inches per year (about .3 to .4 mm/day). However, unlike other mammals whose hair growth is either cyclical or seasonal, ours is not. In fact, each phase or hair growth has its own timeline which can be impacted by a variety of factors. 

There are three main phases of hair growth: anagen, catagen and telogen. These include the growth and maturation of hair and hair follicle activity. Finally, during a phase called “exogen”, hair begins to shed and the growth cycle begins again.(1)

The phases of hair growth 

Firstly, hair begins to grow in the anagen phase. This is the longest phase of the hair cycle. In fact, it can last between 3 and 5 years for your scalp hair. However, the anagen phase differs between types of hairs. For example, the anagen phase for eyebrow hairs is much shorter than for scalp hair. Throughout the anagen phase, hair follicles produce hairs that will grow until they fall out at the end of their lifespan. Approximately 90% of your scalp hairs are in the anagen phase at any one time. 

Then, once the anagen phase is complete, the catagen phase begins. This second phase usually lasts around 10 days. During this time, hair follicles grow smaller and hair grows at a slower rate. Approximately 5% of the hair on our head is in the catagen phase at any given time. Finally, during the telogen phase, the hair enters a “resting” stage. This phase normally lasts for 3 months, during this time hair doesn’t grow but it also doesn’t fall out. In addition, new hairs start to form in follicles that have previously released hairs in the catagen phase. 

Finally, the exogen phase is when shedding starts to take place. During the exogen phase, we may lose between 50 and 100 hairs per day. Moreover, this shedding phase can last between 2 and 5 months, during which new hairs are growing in the follicles where old hairs are shedding.(2)

Hair loss and stress

While normal hair growth appears relatively structured and predictable, what about hair loss? Hair loss is a condition that can affect people of any gender and age throughout life. In fact, there are many causes of hair loss from stress to nutrient deficiencies. High stress-levels have been linked to premature hair-loss conditions. These include telogen effluvium, trichotillomania and alopecia areata. 

Individuals with telogen effluvium suffer from hair loss due to hair moving quickly from the anagen phase into telogen and exogen phases. Thus their daily hair loss can often double or triple. 

Moreover, trichotillomania is a psychological condition in which affected individuals have an urge to pull hair from their scalp or other areas like eyebrows. 

In addition, alopecia areata also leads to hair loss, where hair falls out in small patches. In fact, this condition occurs when the immune system attacks the hair follicles therefore resulting in accelerated and increased shedding. 

However, the good news is that if hair loss is stress-induced, managing stress can be a solution to regaining normal and healthy hair growth.(3) 

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