Does Hair Grow Faster in the Winter?


Even though most people dont think about hair, the science of hair growth is quite fascinating. For example, did you know that your hair is the second-fastest-growing tissue after bone marrow? Or that your head contains between 100,000 and 150,000 strands of hair?

Over the past decade, scientists have tried to figure out the exact time hair grows best. They want to understand its growth cycle, the role of the environment in regulating growth, as well as the roles of genetic and hormonal predispositions in hair loss conditions. A fascinating finding from such research is that hair has different rates of growth during different seasons of the year.

In simple terms, your hair is neither static nor does it grow at a constant rate. Rather, it is sensitive to hormones and genetic factors that interact with and responds to the external environment. But how and why is hair affected by seasonal fluctuations? Let’s explore this more and attempt to answer the burning question: does hair grow faster in the winter?

Does hair grow faster in winter?



No, hair does not grow faster in winter; however, it does begin its growth cycle and shed the least in the winter. The reduced shedding during colder months adds more hair volume for better insulation and gives the illusion of more hair growth in the winter.

To understand exactly why this is and the dynamics involved, we should start by looking at the hair growth cycle. Your hair goes through phases of growth and shedding throughout the years. It begins with anagen, a hair growth phase of generating new hair tissue. Hair in the anagen phase can continue to grow for up to seven years.

Once your hair has completed its growth phase, it moves to catagen, the transition phase, which lasts only 10 days. In catagen, your hair shrinks and detaches from the dermal papilla and moves up through the shaft. Once it reaches the top of the shaft, hair enters the telogen phase. In telogen, hair strands are at rest as another hair begins growing in the dermal papilla. Telogen can last for up to 3 months. Lastly, at the end of their life cycle, your hair strands enter the catagen phase; the phase of shedding. Here, your strands fall from the shaft to leave room for new hair to continue the cycle.

Hair growth is measured by the proportion of follicles in the anagen phase. By knowing the percentage of the entire hair follicle population that is growing new hair, scientists can gauge and compare hair growth rates.

A study published in the British Journal of Dermatology reported that the highest hair growth rates occurred in the springtime, around March. During this time, more than 90% of hair follicles were in the anagen phase. They tracked the rate of growth in the study sample and found that less and less hair was growing through the summer months and the least growth was in the autumn around August and September months when shedding (catagen) also peaked.

However, something interesting happens in the winter and perhaps it can explain the misconception that hair grows faster during cold months when it doesn’t in reality. After hair reaches the highest rates of catagen in the fall, during winter hair shedding decreases. Researchers were curious about this and looked into whether these circannual rhythms had an evolutionary basis. In other words, are there evolutionary reasons why hair sheds the least in the winter?

They found that because the scalp does not have a layer of fat tissue for insulation, it uses hair as an insulator. In the winter months, given the cold temperatures, a higher density of hair would be needed to maintain warm temperatures. The reduced shedding in winter adds to the hair volume for better insulation and gives the illusion of more hair growth in the winter. This illusion is further enforced by the fact that most hair begins growing in the winter and peaks in the spring at 90% of hair being in the anagen phase.

Seasonal hair growth phases



You may notice changes to your hair over the course of a year. Some months you shed a whole lot more while in other months, your hair is voluminous and healthy. You’re also probably wondering if this is because of your internal bodily cycles and worst-case scenario, a sign of more serious underlying health conditions?

Well, the good news is that for most people these changes are perfectly normal and cyclical. And now that you know that hair goes through four phases of growth, which would explain why your hair is so different during some months. But, there is another interesting question. Does hair grow differently throughout the different months? Research findings say yes. Your hair is a dynamic and goes through cycles in response to the external environment.

The majority of hair grows between January and March and sustains a steady pattern of growth during summer. Researchers report that the growth in these hot months is accompanied by average shedding which peaks in the autumn months. On average, people lose about 60 to 80 hairs a day. However, this is much higher in the autumn with the average being at 100 hairs per day. As this hair sheds, it’s giving way for new hair to start growing steadily through the winter and reach the peak growth rate in the spring.

What’s also interesting are the differences in hair growth for different parts of the body. While the head is what most people attend to, looking at other body hairs can tell us quite a bit. For instance, the study that measured hair growth through the seasons also looked at thigh hair and beard growth patterns for comparison purposes. What they found were patterns different from scalp hair growth. Beards grew slowest in January and February and picked up speed from March to July and hitting the highest level of growth of 60% during the summer months. Thigh hair seemed to follow a pattern similar to that of the beard but with much less dramatic differences in growth rates. It is clear that beard and thigh hairs were not on the same growth and shedding schedule as scalp hair.

This tells us that not all hair in our bodies is regulated the same and it further shows that these differences are the results of evolutionary adaptations that force scalp hair to have the highest fluctuations of growth through the seasons. This also points to the hair cycle and how it is not just scalp hair that goes through the four phases, but hair everywhere in the body.

Androgens and human hair growth



Although there are obvious changes through the seasons, a deeper understanding of why this happens must also look at biological influences on hair growth. Although there a number of biological factors that influence hair growth, one, in particular, stands out, and that is the hormone androgen.

Androgens are hormones associated with the development and maintenance of male characteristics. They are found in both and females and research has cemented their relationship to hair growth. For instance, research published in the Dermatologic Therapies journal reported a relationship between the low levels or absence of androgens and hair loss.

How does that happen? Let’s first look at how these hormones operate to regulate hair growth. Androgens circulate in the blood either as free molecules or by binding to proteins. The hormone then fuses with a cell by binding into a specific nuclear receptor. These receptors have switches to activate or deactivate relevant genes as instructed by androgens. This is precisely what happens when your hair grows. Androgens direct hair growth activity by working with androgen receptors in the hair follicle. These receptors are instructed by androgens to turn certain hair growth-related genetic codes on or off. That is how your hair knows when it’s time to grow, how long to keep growing (between two and seven years) and how to progress through the rest of the hair cycle.

In addition to directing hair growth, androgens are able to alter the size of the hair follicle and the diameter of the fiber; hence regulating the kind of hair you'll grow. Thick, thin, fine, curly--you name it. Research findings suggest that the hair follicle size depends on the volume of the dermal papilla, which is also regulated by androgens.

We see another layer to the story here that involves our hormones and genetic factors. That hair growth and loss is a result of interactions between androgens and the seasonal demands of the body. The seasons signal the body to produce needed amounts of androgen and direct the androgens then go on to regulate hair growth from hair follicles.

With this understanding of hair growth, you should now have a clear understanding of why your hair changes throughout the seasons. You now know through evolution, your body has learned to protect itself by tuning to environmental cues and signaling internal regulators to make needed changes. That is why more androgens are produced in the winter to activate hair growth and slow down hair shedding to protect your head against the cold temperatures.

Sources:

http://www.nwpii.com/ajbms/papers/AJBMS_2015_2_05.pdf

https://sci-hub.se/https://www.ncbi.nlm.nih.gov/pubmed/2003996

https://sci-hub.se/https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1529-8019.2008.00214.x

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4437968/

https://onlinelibrary.wiley.com/doi/epdf/10.1111/bjd.16075



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