Why does hair grow faster in the summer?

[jujube]

Lately I've been wondering why my growth rate had slowed down, before realizing that winter is finally here. We pretty much all noticed our hair grows faster in the warmer months, but I was wondering why is that so?

[Becky Safari]

Mine actually grows faster in the winter, but that's because I put it in protective styles more often. Maybe for others it's the opposite because it's hot in the summer and you want your hair off your neck...:shrug:

[jujube]

I heard it actually had to do with the heat increasing blood flow to your head, is that true?

[Igor]

I would swear we had a thread with a poll on this, unfortunately I cant seem to find it. A lot of people, maybe even the majority here on LHC, has seasonal growth variation. Some people have it in the summer, some in the winter. I think its about 50/50 actually

[spidermom]

I'm pretty sure it's because of the angle of the sun and the hours of daylight.

[monsterna]

I'm pretty sure it's because of the angle of the sun and the hours of daylight.

Then this leads me to ask if sunlight is good for hair health/growth... or is it from the vitamins we get from sunlight?

[Night_Kitten]

I don't think direct sunlight is very good for hair (because of the UV)
Perhaps it has to do with the daily hormone cycles that are affected by the ammount of "light hours" in a day?

[Jeno86]

I read somewhere that in winter, your body goes into survival mode to it tries to store all the vitamins and nutrients as it can also the blood flow it a bit restricted. If this is true then it means in the summer, your body is relaxed so you have not only better blood flow but more of the good stuff your body needs.

[jojo]

My hair stalls every summer but grows much faster in winter, I like in the North West of England and its very cold here, summers dont really happen over here apart from the odd few weeks of sunshine. I go away every year twice to warmer climates and it has no effect on my growth.

[brunetka]

I would swear we had a thread with a poll on this, unfortunately I cant seem to find it. A lot of people, maybe even the majority here on LHC, has seasonal growth variation. Some people have it in the summer, some in the winter. I think its about 50/50 actually

It would be interesting to look at the distribution of those answers over geography (where you are in relation to the equator, during which months you get the most sunlight, and how much sunlight levels vary over the year for you), urban vs rural living, and lifestyle (how much your environment and lifestyle affect how much sunlight you get and your circadian rhythms).

There is an article on the topic here http://onlinelibrary.wiley.com/doi/10.1111/j.1529-8019.2008.00214.x/full
that may or may not be accessible for you, so I'll post some quotes


Androgens and hair growth
Valerie Anne Randall
Dermatologic Therapy
Volume 21, Issue 5, pages 314–328, September/October 2008


Hormonal coordination of seasonal changes in animals
Seasonal changes usually occur twice a year in many mammals living in temperate or polar regions with coordinated waves of growth and moulting to produce thick, warm winter coats and shorter summer pelage. These are linked to day-length and, to a lesser extent, temperature, such as seasonal breeding activity (17,47). Nutrient availability can also affect hair type because of the high metabolic requirements of hair production (48 ). Studies in many species show that long daylight hours initiate short periods of daily melatonin secretion by the pineal and summer coat development, while short day-length increases melatonin secretion and stimulates a longer, warmer pelage (47,49 reviewed in 1,17). The pineal gland acts as a neuroendocrine transducer converting nerve impulses stimulated by daylight to reduced secretion of melatonin, normally secreted during the dark. Melatonin signals are generally translated to the follicle via the hypothalamus–pituitary route; prolactin particularly, but also growth hormone and IGF-1 are implicated at the follicle level (reviewed in 1).

Other hormones implicated in regulating mammalian hair growth cycles include the sex steroids, estradiol and testosterone, and the adrenal steroids (1,17); these delay anagen in rats (17,50).

Seasonal changes in human hair growth
Seasonal alterations are much less obvious in human beings, where follicle cycles are not usually synchronized after the first year, other than in groups of three follicles called Demeijère trios (45). Regular annual cycles in human scalp (3–5) and beard and other body hair growth (3) were only recognized relatively recently. Scalp hair showed a single annual cycle with over 90% of follicles in anagen in the spring, falling to around 80% in autumn in 14 healthy Caucasian men aged 18–39 in Sheffield, UK (latitude 53.4°N); the number of hairs shed in the autumn also more than doubled (3). Similar increased autumnal hair shedding has been reported in New York women (4) and French men (5). Since scalp hair usually grows for at least 2–3 years and often longer (45), detection of an annual cycle indicates a strong response to seasonal hormonal changes by any follicles able to react, presumably those in later stages of the hair anagen phase.

Androgen-dependent body hair also showed annual changes in men (3). Winter beard and thigh hair growth rate were low, but increased significantly in the summer (see (1)). French men showed similar summer peaks in semen volume, sperm count and mobility (57) suggesting androgen-related effects, while higher summer testosterone levels with lower winter values were also reported in European men (58,59) and pubertal boys (60). Although testosterone changes probably alter beard and thigh hair growth, they seem less likely to regulate scalp follicles as women also show seasonal changes. Annual fluctuations of thyroid hormones, with peaks of thyroxine (T3) in September and free triiodothyronine (T4) in October (61), could also influence scalp growth, but hypothyroidism is normally associated with hair loss (62).

Thigh follicles also showed biannual changes in the numbers of hairs actually growing, reaching 80% in May and November, but falling to around 60% in March and August (3). This pattern is similar to the spring and autumn moults of many temperate mammals and our seasonal study population definitely exhibited seasonal behavior despite indoor occupations (3); these cycles are presumably controlled like those discussed earlier in “Hormonal coordination of seasonal changes in animals.” Human beings can respond to altered day-length by changing melatonin, prolactin, and cortisol secretion, but artificially manipulated urban lighting suppresses these responses (63). Nevertheless, people in Antarctica (64) and those with seasonal affective disorder (65) maintain melatonin rhythms.

[fairy_ends_girl]

wow brunetka, very interesting!! Thanks for posting :)

[IndigoAsh]

I tend to go through hair growth spurts in the fall and winter. That info a couple posts back was super awesome!

[jujube]

Wow, I thought the "hair grows faster in summer" thing was true for everyone, I'm surprised that so many of us experience growth spurts in the winter.

[Buddaphlyy]

My hair grows faster in winter, always has. Even without protective styles, I usually grow and retain more hair between January and April of each year.

[thatjengirl1]

i agree with Igor, ive heard people differ. some people have growth spurts in summmer months and some in the winter. i'm not sure what i am yet. this is the first winter i've gone without trimming and its growing about 3/4 inch a month. we will see what summer brings :)

[Lianna]

Wow, I thought the "hair grows faster in summer" thing was true for everyone, I'm surprised that so many of us experience growth spurts in the winter.

Nothing is true for everyone. I live in a tropical country where even the winter is sunny most of the time, and quite warm. I've only measured my hair the 2 times I grew out a pixie (yeah, LOL). It was the same, average growth. Now after some growth aids I see more growth.

[jaine]

I wonder if those of you experiencing winter growth spurts are keeping your house at a warmer temperature than my landlord keeps mine!!
shudder: