A commonly touted notion is that your hair will grow faster, be thicker, and otherwise naturally longer in the winter time thanks to the supposed evolutionary benefit to help keep you warm in the colder months. But is this actually true? And what about beards?

As to the former, yes and no. As to the latter, it turns out something more interesting is going on with beard growth cycles. Let’s jump into it shall we?

First, it’s important to understand how hair growth cycles actually work. Hair length is completely controlled by the length of the anagen phase of your hair follicle.  How long this period lasts is generally determined mostly by genetics and hormones, with factors like extreme stress, nutrition, and activity levels influencing the latter.

Following the anagen phase is the catagen phase.  It isn’t yet fully understood all the factors that go into triggering the catagen phase, but once it is triggered, the outer part of the root ends up being cut off from its nutrient supply (blood), as well as the cells that produce new hair, thus your hair stops growing. This phase lasts about three weeks.

Next up comes the telogen phase where the follicle is in a resting state and your hair is now a “club hair”, completely dead down to the root.  During this stage, these hairs are relatively easy to pull out (as can happen while brushing/combing/washing your hair), but if they manage to last long enough, they’ll eventually be pushed out by a new hair as the cycle begins again.

Obviously hairs on your arms or legs have a very different anagen period than hairs on your scalp, thus why your leg hair doesn’t grow two feet long without trimming.  Further, different people, thanks mostly to their genetics, have differing lengths of the anagen period for a given body part compared to other people.

For the hair on your scalp, the average length of the anagen phase is about 2-7 years.  For your arms, legs, eyebrows, etc., this phase usually lasts just 30-45 days.  However, in extreme cases which are quite rare, some people have anagen periods for their scalp hair as small as most people’s anagen phases for their arms and legs. For these people, their scalp hair never naturally grows more than a few inches long.  The opposite is also true, with very rare individuals whose anagen phase can last decades for their scalp hair.

At any given time about 85%-90% of your hair is in the anagen phase, 1-2% is in the catagen phase, and 10-14% is in the telogen phase.  However, extreme stress can trigger the anagen phase to stop prematurely and hair can rapidly progress to the telogen phase, even as much as 70% of the hair on your body at once. When this happens, the majority of your hair that should still be growing can fall out more or less all at the same time.

This all brings us around to seasons and what effect this has on your hair. It turns out studies have shown that while your overall growth rate of much of the hair on your body doesn’t change significantly from month to month, there is a difference in density thanks to the peak percentage of hairs in the anogen (growth) phase in certain months and peak percentage of hairs in the telogen (dead/falling out) phase during other months.

For example, a study Seasonality of hair shedding in healthy women complaining of hair loss, looking at 823 women over 6 years noted a marked and relatively consistent trend of periodic shedding, with peak density of hairs in the telogen (falling out) phase in the summer, and another small spike in spring as the weather starts to warm. The lowest rates, and thus highest rates of the anogen (growth) phase were in the winter, maximizing the density of hairs on your body. That said, the differences here are relatively slight, as we’ll get into shortly, so this isn’t likely to actually make any real difference in keeping humans warmer or not, even if one were simply to let their hair grow out for maximal insulation.

But what about beards? You may or may not be surprised to learn that this is an area that very few researchers have thrown their brain power at. Thus, while we couldn’t find any data on density of beard hairs in anogen/catogen/telogin phase by season, there does exist one study tracking beard hair growth rates by month that reveals something rather interesting.

It turns out, the data so far seems to pretty strongly indicate that beard growth is actually maximized not in the winter, but the summer. This actually makes sense when you look at the underlying mechanisms behind beard hair growth and its hypothesized connection to mating, the latter of which we’ll get into in the Bonus Facts in a bit.

But first, the study, Seasonal Changes in Human Hair Growth, published in 1991, looks at a group of British men aged 18-39, tracking their beard growth and activities for 18 months.

In the study, the researchers also confirmed what others have likewise shown- that scalp hair, for example, has a peak amount of hair in the anogen (growth phase) in the winter. In their study, they observed that peak anogen phase around February/March at approximately 90%, then falling steadily from there until September then climbing back up. They also directly measuring about 60 hairs lost per day from the scalp at peak telogen phase time (in the summer) and about half that rate during the winter.

As for beards, they observed that the growth rate of beard hair actually peaked in June and July and was at its lowest in January and February. Not a subtle difference, the peak growth rate in the summer months was 38% faster than in the lowest growth rate months of January and February.

Bizarrely, the rate of growth in these men’s thigh hair more or less mimicked the general growth cycle of the beard hair, albeit without as much of a contrast between the lowest growth rate months and the highest.

Now, one thing to note about this is that there has been very little research done on rates of beard hair growth and, for example in this study, the sample size was only 14 men and all who had indoor jobs. This is potentially significant given what is hypothesized to be causing the difference. If the hypothesis is correct, men who, say, live in southern California and work outdoor jobs may see little variance in beard hair growth from season to season.

So what’s thought to be causing the change? First, the researchers noted that the men were significantly more active in the summer and spent more time outdoors. It is hypothesized from this that the increased activity outside results in things like more exposure to sunlight and boost in Vitamin D, change in melatonin secretion (which in turn effects prolactin secretion), along with various other hormonal changes that follow from all that, including a slight boost in testosterone. These all seem to play their parts in seasonal changes observed in our hair, both in the very slight cycles in seasonal shedding and, particularly in the case of testosterone, change in growth rate of the beard.

So how does testosterone do this? It turns out, not directly. The extra testosterone ends up resulting in the creation of a much more potent sex hormone called dihydrotestosterone (DHT), with the enzyme 5α-reductase, facilitating the conversion of testosterone to this, including this conversion happening in hair follicles.

From there, different hair follicles on your body react differently to DHT. Pertinent to the topic at hand, DHT seems to be a major factor in male pattern baldness. (More on this in a bit.) On the other hand, the hair follicles in your face, end up getting stimulated by DHT causing an increase in hair growth rate.

Thus, more testosterone means more DHT stimulating your facial hair growth, and thus in the summer when you’re more active and the like, your beard grows faster. Or, at least, that’s the working hypothesis at the moment. Again, beards are not exactly something many scientists are earning their PhD’s with research projects on. But at least the data at hand seems to be leaning this way.

Now, noteworthy here, contrary to popular belief, men with thick, flowing beards do not necessarily have more testosterone than their patchy or naturally bare-faced brethren. As dermatologist Dr. Jennifer Chwalek states: “Men who can’t grow a beard or have patchy beards usually have normal testosterone levels. It isn’t a reflection of having low testosterone or being deficient in testosterone.”

It turns out that, while there are certainly many exceptions, most men of a given age and general fitness, nutrition level and the like have in the ballpark of the same amount of testosterone as their compatriots with the same fitness level, age, etc. Thus, the difference in beard hair growth usually isn’t so much about a significant difference in testosterone. If it was, you’d not have so many elderly men with their long, flowing beards, for example. Rather, it more comes down to genetics, and in turn the results of that- like the density of hair follicles on your face and their sensitivity to DHT in the first place, which can vary considerably from man to man.

As Dr. Chwalek sums up “Some men… have more hair follicles, so they can grow denser, coarser beards than others. Testosterone gets converted in the hair follicle to a more potent form called dihydrotestosterone. Some hair follicles have receptors on them that are very sensitive to this higher form of testosterone, dihydrotestosterone, and that will stimulate hair growth.”

Thus, men whose facial hairs are like the drama queen’s of hair follicles (super sensitive), end up producing magnificent beards when combined with a high density of hairs.

This brings us to the question of why bald men seem to be able to grow the best beards., While we could find no scientific study done on whether bald men actually do grow thicker and longer beards than their hairy scalped compatriots, the perception certainly exists and there may be something to it.

As alluded to, an interesting thing about DHT is it seems to be a major contributor to male pattern baldness, with scalp hair reacting differently to it than facial hair. But if the extra sensitivity is there for both facial and scalp hair, in one case it may result in an increased likelihood of the man going bald, while in the other case, it may well result in a magnificent beard. Though, again, we couldn’t actually find anyone whose done a study on this, but it seems a reasonable hypothesis given the data at hand, with further research needed to determine things definitively.

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Bonus Facts:

While we could find no study looking at pubic hair growth by season, it’s noteworthy that other studies have indicated DHT has a similar affect on pubic hair as facial and thigh hair, meaning it could be hypothesized that there may be a seasonal growth rate change in one’s nether regions mimicking the acceleration of beard growth in the summer. Given other studies have shown sperm count, semen volume, and sperm mobility also peaks in the summer for many men, and it’s hypothesized that pubic hair has remained on humans (along with armpit hair) to help attract the opposite sex via certain pheromones, this would also make sense here. (For more details on this, see our article, Why Do We Still Have Pubic and Armpit Hair?)

Further, beards have likewise been connected to mating via a surprising number of studies looking into the connection with beards and attractiveness. On this, studies pretty consistently show that women en masse find men with stubble to short beards the most attractive. However, there is another element that may favor men with long, full beards in terms of actual desire to mate with said man. For example, in the 2013 study The role of facial hair in women’s perceptions of men’s attractiveness, health, masculinity and parenting abilities the researchers found that while the majority of women perceive men with long, thick beards as more masculine then men with closely trimmed beards or clean shaven, when women are most fertile in their cycle, their ratings of the masculinity of men with full beards increased even more.  Further, the women in the study also consistently rated men with long, full beards as more likely to be better fathers and more socially mature. As the researchers sum up of their research, this “suggest[s] that an intermediate level of beardedness is most attractive while full-bearded men may be perceived as better fathers who could protect and invest in offspring.”

Further, this and other studies have likewise shown that women consistently rate bearded men of all levels as healthier than their bald-faced compatriots. Thus, all combining to potentially give a benefit to faster beard growth at times when male sperm counts and motility are the highest- the warmer months when historically resources for baby making are at their peak.

Finally, to debunk a myth, as you might have now guessed from the fact that hair growth is completely controlled by what’s going on under the surface, within your hair follicles, and that genetics and hormones are the primary things determining hair growth length and rate, which are in no way affected by shaving- contrary to popular belief, shaving does not in any way alter your hair growth rate nor does it alter the color of the hair, nor thickness. Study after study has shown this, and it just makes sense when you understand the mechanisms behind hair growth.

There is one exception to this- waxing. With waxing it is possible to affect the thickness and other aspects of hair regrowth. However, it will never be the case that the hair will grow back thicker/darker/faster. It actually goes the other way. With waxing you are damaging the hair follicles underneath the skin; over time as you wax more and more, the hair will grow back less and less and even sometimes will get lighter colored and thinner. So though waxing, unlike shaving, actually does affect your hair growth, it more or less affects it in the opposite way most people think shaving does.

Illustrating this in a rather humorous way, in the film The Reader (2008), actress Kate Winslet was having a bit of trouble growing out her pubic hair to the satisfactory of the filmmakers (owing to, as she put it, “years of waxing”); so they had a merkin (vagina wig) made to cover the area instead. Winslet, however, didn’t care for the thing and stated in an interview she told them, “Guys, I am going to have to draw the line at a pubic wig, but you can shoot my own snatch up close and personal.”

The problem is that film makers need the hair to avoid an NC-17 rating. If the actress’ nether regions are sufficiently concealed by hair, the MPAA will sometimes look the other way and give a film a less restrictive rating, depending on how exactly said region is shown in the movie.  If the bare lady bits are shown, however, even briefly, getting a less restrictive rating is much less likely. Thus, erring on the side of caution, most directors will instruct the bare ladies to either grow out their hair down there for nude scenes or put on a merkin.