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This site describes a very detailed, methodical study and is supported by careful analysis and empirical data.
This is no surprise to me as I've always *known* that my hair grows faster in summer.
Study of season hair growth
Thanks, it was interesting to read.
What a great find, Jason. Thanks for posting it. It is wonderful to learn hair is being studied, it kinda gets medically ignored for the most part since it is a body part that doesn't get sick in any life threatening way.
It would be neat to know which site his study subject participates on. That monthly growth spike was a surprise and all the more reason to study more people, especially men, to tease apart factors. Most interesting was that finding of what looks like faster growth after trims. That's counterintuitive since growth comes from the scalp and not the ends affected by the trim.
I haven't worked it out yet but I'm guessing it is not an actual increase but the regular growth that is becomes observable when starting from a blunt line. I can't help but think it would be easy enough to study by only trimming half of the subject's hair during the study. If there is a growth bonus, the untrimmed side would be less in length than the total of the trimmed side and trim loss added to the figure.
Elizabeth
Actually what you said last seems pretty hard to verify. Considering hair may grow at different speed and you might catch some 'gallopers' like mentioned, and notice a variation over a shorter-growing hair and a faster one. Also, it's measured in millimeters, and all factors can't be ruled out - with 39~45 inch of hair, you'd expect your hair could get sat on, stuck in places, and I propose that might visibly shorten it by a few millimeters.
Also, the trim vs non-trim was a surprise to me. If it treats split ends and nearly removes the lenght-loss by faster growth, that's great, but I doubt it could be cross-referenced to doing half the hair.
Let me say why with an example:
-Trim hair by 6 mm, it grows back 8 mm (variation +2 mm)
-Don't trim hair, it grows by 4 mm (variation +4 mm)
Trimming would still shorten it a bit, though negligedly so while potentially helping the tips of the hair (split ends and such) have an healthier appearance.
This seems worth exploring nevertheless, it just seems hard to do.
Sara Melissande
Sara, you got me thinking. Loss at the bottom can be ruled out by only measuring growth at the top. I've seen girls with hair wraps kept in for months. Something like that would provide a more precise fixed point of reference. My bet is that a trim on the end of that would not show a change in growth speed.
Elizabeth
Yeah...I didn't find this particularly convincing.
As I went through it I saw mention of several irregularities in measurements/calculations as well as admissions of possible unknown factors.
He listed sources which is good and there were lots of pretty graphs and lots of formal wording but that doesn't always mean much.
The end of the article where the conclusions are drawn was not very conclusive though they did make a statement based on the study of one female despite unknowns, untested ideas and variables not taken into consideration.
Basically, it sounded nice but there wasn't a whole lot of content to support the conclusion. Remember that this was about as basic as you can get since only one subject was used and apparently showed a very slight growth rate difference that may or may not have been due to the reasons they were focusing on in the study. Also, some of the "phenomenon" which they made conclusive statements about did not come with explanations about how they supposedly worked.
If this article showed anything it was more about hormones and hair growth cycles which is what we have known for a long time (I have a link to such info in the R.A.Q.).
I don't really want to criticise the author but his creds list him as a Master of Business Administration which is irrelevant to the study subject (just mentioning it because he displays it as if it might mean something). The site which published the article seems to display an odd variety of different subjects and charges a fee of $300 to be published. And though it says it submits all articles to peer review it follows it by saying that the publisher can deem certain articles to skip the peer review. Was it peer reviewed or not? I see a lot of red flags that would get in the way of it being a solid study.
Hair Religion
It's not definitive proof, what it does show is a statistically significant difference in the rate of hair growth by season in a particular individual. There's not a single mention of protein, food or eating habits at the web site, and if one is to believe that protein intake has an effect on hair growth, the extra length in summer could be due to eating more protein (eg. BBQ).
Yes it is definitive proof. Diet is all part of seasonal differences (ie: fresh fruits and vegetables) that could contribute to an increase in summer. Most likely diet has little to do with it. The data are there. If you choose to disbelieve the study, that's your prerogative but numbers don't lie.
Numbers can show something is happening but not the cause, I don't even find the method of measuring accurate so the numbers may not even say what they have been interpreted as. Besides, if it is diet then it is not summer, those are different factors. Maybe it is less stress she experienced during the summer so again that would not be summer itself.
Revan is right that this single case is not proof, that takes large samples and many studies to establish. The study author didn't even know enough about individual hair's growth over the lifespan to understand the cause of those 'gallopers' he noticed. One unprofessional study is never proof.
Elizabeth
Weight is also given in my mind to the tremendous anecdotal evidence in favor of increased growth in summer. This study clearly showed there was a seasonal difference. It's easy to criticize the study but then you would have to come up with an explanation for the seasonal differences. It is highly conjectural to try to say it's barbeques or summer vacation that led to this. I think the evidence is there that is a *seasonal* difference and life style factors had little or no relevance.