Math behind the average growth?

[Milynn]

This is probably utterly stupid thing to wonder about, but - well. I bet you are smarter than me, so I will ask nonetheless.

In short, what does the claim "average growth is 0,5 inches per month" takes in account? Does hair actually grow that much, if we eliminate possible breakage from the function? Meaning, how does the average amount of shedding impacts to this claim?

Wondering, as lets say average amount of shedding is 40 hairs per day. Could be less, could be more, playing only with averages here. If there is, lets say, 100 000 hairs average, 95 % of them growing... 95 000 hairs in growth phase. By average, individual hair grows 0,04 cm per day (totals in 1,2 cm per month). In total, 95 000 hairs grow 114 000 cm per month, or 3800 cm per day. Huge amounts, when listed this way...

However, lets say you lose 40 hair per day. Lets say those hairs are 50 cm long, each one of them. Total lose would be 2000 cm per day (one again, sounds scary). Which leads the net gain to be 3800 - 2000 = 1800 per day, meaning 54 000 cm per month or ~ 0,5 cm per month. Resulting not 15 cm amount of NET growth in a year (average, 6 inch) but 6 cm instead (under 3 inch).

Yet, it seems that usually the NET growth from year to year tend to be around 12 - 15 cm, without trims. Including shedding. What am I missing? Has the average amount of shedding been included in that average amount of growth - claim?

In reality, I am very number oriented person and thus I try to solve my breakage obsession by counting (how many individual 1 - 2 inch hair I can lose a day without it completely stunting my new growth), but as I do not know the base assumptions, I could not finish - I get two very different results, and the shedding part is the key. (As without shedding even 50 little one inch long hairs in a day would not really effect that much. From the math is seems that the breakage really does not have that big of an impact, as 50 x 2,56 x 30 (days) equals only to 3840 cm (month) or 128 cm per day, which is nothing compared to average growth numbers (114 000 per month or 3800 per day).

How do I include shedding to this all?

I apoloqize if I am being an idiot :D

[neko_kawaii]

Understanding the growth and rest phases might help. https://en.m.wikipedia.org/wiki/Hair_follicle

[Milynn]

Thank you for the reply!

I think I do understand the phases though. I re-read that Wikipedia article, especially the growth -section. I still did not really found a solid answer.

I am thinking now that when counting those things I should not include shedded hair in that equation at all, which of course would be a huge relief. (As that would mean that the breakage should actually be huge every day to actually have an impact, not just 50 inch long strands or so).

[Laurab]

You're not being an idiot at all!
Just maybe overthinking it?

I think most people just take a tape measure and check how much their hair has grown from one month to a next, and for most people that number hovers around half an inch. It's not super scientific, from what I've seen. And really, I think there are too many factors to ever make it super scientific.
A good science experiment is able to keep everything consistant and just change one thing.
hair growth depends on things you've mentioned like shedding and breakage, along with diet, genetics, exercise, weather, stress levels, hair texture, basically just way too many things to get a consitant number on.

I totally get what your thought process is here, and I can say from personal experience when you get too caught up on the details it doesn't help longterm. It's that saying, you can't see the forest through the trees, or however it goes. If you're able to get your mind off of it for a bit your hair will grow faster than you realize.

[Milynn]

You're not being an idiot at all!
Just maybe overthinking it?

I totally get what your thought process is here, and I can say from personal experience when you get too caught up on the details it doesn't help longterm. It's that saying, you can't see the forest through the trees, or however it goes. If you're able to get your mind off of it for a bit your hair will grow faster than you realize.

Thanks for the kind words :)

I might indeed be overthinking it. It just as a number oriented person, this is my way of reducing stress - as there has been some bleach damage and protein overload damage on my hair, there has also been some breakage. Which totally made me freak out. I have now done everything I can to help it, but I still stress about it, which is probably normal. Yet, stress itself is bad... That's why I tried this counting thing - If I could tell myself it is not mathematically likely to lose all new AND some old growth due to breakage, it would reduce the stress. Otherwise I am somewhat content with my hair length - just afraid of losing it.

[EdG]

Here is some simple math with average numbers.

An average person has 100,000 hairs on his or her head. The person sheds 100 hairs per day. This implies that the duration of an individual hair's growth cycle is 1,000 days. With an average growth rate of 0.5 inches/month, the hair's terminal length is 16 inches.

These numbers can vary widely even among hairs on the same person!
Ed

[auburntressed]

Honestly, I don’t think the half in a month figure takes breakage or anything else into account besides how much root grows out of your head. I don’t know what scientific study or studies concluded this. There would need to be multiple studies done by different people, all of which can be peer-reviewed and critiqued openly before anything like a scientific consensus could be properly reached, and I’m not sure that has actually been done for hair growth rates.

However, there have been stylists who color hair around for a long time. My suspicion is that they eventually noticed people tend to grow a half inch of roots that then need to be covered up each month. And from there, it spread into the popular wisdom.

[MusicalSpoons]

Shedding and breakage are two different things. Shedding is entirely natural and doesn't affect the other hairs still attached on your head. Breakage is largely unnatural (though inevitable to some extent for many of us, even with virgin hair).

Breakage is the problem if you want to retain length - roughly half an inch of each hair grows out of the follicle per month on average* and if every hair (or most of them) is breaking off at the end, you won't gain the full half inch of extra overall length. Whereas if only a few hairs break off at the ends, it won't have much of an impact on overall length.

*I don't know where that number came from either but it seems to hold largely true here. As with all averages, you'll get some people with less or more growth.

[Dark40]

I second MusicalSpoons.

[Milynn]

Thanks for the replies, there has been good points pointed out! Perhaps it indeed isnt' useful to try to count this in "scientific" way, it being just one of those things which just "are". Strange though, I would bet there are some studies concerning hair growth... but yeah, perhaps this particular one is indeed too tricky to organize and supervise.




Breakage is the problem if you want to retain length - roughly half an inch of each hair grows out of the follicle per month on average* and if every hair (or most of them) is breaking off at the end, you won't gain the full half inch of extra overall length. Whereas if only a few hairs break off at the ends, it won't have much of an impact on overall length.


Yep, this was precisely what I was - and am - worried about, initial reason for trying to count this thing (as there is some line where "every hair vs a few hairs" makes that difference whether you see the growth or not. I am indeed inpatient, I could definitely just wait and see how it turns out... but I am missing that attribute :D).

[Tiliantti]

I only make some rough approximation of how much length I have gained in a year (if I have not trimmed) and then divide it by 12. Seems like I am getting quite steady 15 cm per year, so it is about 1,25 cm (half inch) per month. This of course doesn't take to account any shedding or breakage, and there might be some variation between month or seasons, but that's about the average.

[spidermom]

I am also of the opinion that you're over-thinking this. Put very simply, if someone dyes their hair, they could expect to see an average of 1/2 inch of natural color at the scalp in one month.

Of course, everybody revolves around average. One person might see 1 inch of new growth and another only 1/4 inch; plus everything in-between.

[ynne]

Is the entire post about breakage, instead of shedding? I think mechanical breakage (e.g. around shoulder length) can indeed make a person stuck at fake terminal length, but since yours is probably caused by the bleaching etc., it really depends on how fragile it is. I don't know if you are stopping with dyes or continuing, but both approaches have their own threads (continuing (https://forums.longhaircommunity.com/showthread.php?t=125938) and stopping (https://forums.longhaircommunity.com/showthread.php?t=51155)) where you might find support and success stories to motivate you!

I hope you find a way to take your mind off of things. :)

[Milynn]

Is the entire post about breakage, instead of shedding? I think mechanical breakage (e.g. around shoulder length) can indeed make a person stuck at fake terminal length, but since yours is probably caused by the bleaching etc., it really depends on how fragile it is. I don't know if you are stopping with dyes or continuing, but both approaches have their own threads (continuing (https://forums.longhaircommunity.com/showthread.php?t=125938) and stopping (https://forums.longhaircommunity.com/showthread.php?t=51155)) where you might find support and success stories to motivate you!

I hope you find a way to take your mind off of things. :)

It is about both, I know the difference :) I was trying to balance the function X (shedding) + Y (breakage) = Z (new growth). Basically, how much you nee both of those to equal zero new growth. But yeah, this is probably impossible to count. Thank you all nonetheless, I do feel better! And slightly sorry for this topic :D Bleaching was one time experience for me, to get black out of my hair and to continue use Henna or elumen, probably henna.

[erebus]

This is probably utterly stupid thing to wonder about, but - well. I bet you are smarter than me, so I will ask nonetheless.

In short, what does the claim "average growth is 0,5 inches per month" takes in account? Does hair actually grow that much, if we eliminate possible breakage from the function? Meaning, how does the average amount of shedding impacts to this claim?

Wondering, as lets say average amount of shedding is 40 hairs per day. Could be less, could be more, playing only with averages here. If there is, lets say, 100 000 hairs average, 95 % of them growing... 95 000 hairs in growth phase. By average, individual hair grows 0,04 cm per day (totals in 1,2 cm per month). In total, 95 000 hairs grow 114 000 cm per month, or 3800 cm per day. Huge amounts, when listed this way...

However, lets say you lose 40 hair per day. Lets say those hairs are 50 cm long, each one of them. Total lose would be 2000 cm per day (one again, sounds scary). Which leads the net gain to be 3800 - 2000 = 1800 per day, meaning 54 000 cm per month or ~ 0,5 cm per month. Resulting not 15 cm amount of NET growth in a year (average, 6 inch) but 6 cm instead (under 3 inch).

Yet, it seems that usually the NET growth from year to year tend to be around 12 - 15 cm, without trims. Including shedding. What am I missing? Has the average amount of shedding been included in that average amount of growth - claim?

In reality, I am very number oriented person and thus I try to solve my breakage obsession by counting (how many individual 1 - 2 inch hair I can lose a day without it completely stunting my new growth), but as I do not know the base assumptions, I could not finish - I get two very different results, and the shedding part is the key. (As without shedding even 50 little one inch long hairs in a day would not really effect that much. From the math is seems that the breakage really does not have that big of an impact, as 50 x 2,56 x 30 (days) equals only to 3840 cm (month) or 128 cm per day, which is nothing compared to average growth numbers (114 000 per month or 3800 per day).

How do I include shedding to this all?

I apoloqize if I am being an idiot :D

I think you are conflating things here. You're trying to calculate the total length of all your hairs added together, whereas the 0.5" / month growth that is said to be average is an empirical estimate of the growth of your ends. The 6 cm number you arrived at to some extent reflects the fact that hair density decreases with length, but in that case it would be much better to talk about the distribution of hair strand lengths. Anyway, your ends probably grow at the same rate as an average strand, and any breakage just thins them out. Shedding also thins them out as they grow, since not all follicles will have an equally long anagen phase (there is some statistical distribution).

A bit unrelated, but I was reading some papers on hair growth phases a while ago, and was surprised how many hairs they found to be in the very early anagen phase in the people they studied. The amount of follicles growing more than a few years was minimal.

[ynne]

It is about both, I know the difference :) I was trying to balance the function X (shedding) + Y (breakage) = Z (new growth). Basically, how much you nee both of those to equal zero new growth. But yeah, this is probably impossible to count. Thank you all nonetheless, I do feel better! And slightly sorry for this topic :D Bleaching was one time experience for me, to get black out of my hair and to continue use Henna or elumen, probably henna.

Oh, but the growth rate is about individual hairs, how would shed strands affect the growth gain of the ones that remain? Since there is always going to be hair in different stages of growth, and of drastically different lengths, the hair length measuring is usually of the overall length, not added from all hair. That's why I got lost and assumed you were just talking about breakage. :) But erebus explained it better than me. I hope you will enjoy henna (or elumen), mine was originally over bleached hair too and it turned out pretty well, imo!

[MusicalSpoons]

It is about both, I know the difference :) I was trying to balance the function X (shedding) + Y (breakage) = Z (new growth). Basically, how much you nee both of those to equal zero new growth. But yeah, this is probably impossible to count. Thank you all nonetheless, I do feel better! And slightly sorry for this topic :D Bleaching was one time experience for me, to get black out of my hair and to continue use Henna or elumen, probably henna.


Oh, but the growth rate is about individual hairs, how would shed strands affect the growth gain of the ones that remain? Since there is always going to be hair in different stages of growth, and of drastically different lengths, the hair length measuring is usually of the overall length, not added from all hair. That's why I got lost and assumed you were just talking about breakage. :) But erebus explained it better than me. I hope you will enjoy henna (or elumen), mine was originally over bleached hair too and it turned out pretty well, imo!

Exactly. Shedding only affects overall length gain if your longest hairs are at terminal length, or if lots of hairs shed prematurely (telogen effluvium) such as caused by major or prolonged stress - and once the hair goes back to its normal growth cycle, shedding would no longer be affecting overall length. I don't know how long your hair is but only a few members here have reached their (true, genetically-determined) terminal lengths, with most of those being around calf or longer.

Put very simply, if your hair is breaking off at the same rate or faster than it's growing, you'll either stay at the same overall length or lose length.

[Milynn]

Put very simply, if your hair is breaking off at the same rate or faster than it's growing, you'll either stay at the same overall length or lose length.

This is what I was after as I was not sure (whether to include shedding to this as well) - thank you. And others as well, and especially erebus for your detailed answer - indeed, distribution would have been correct term here. My breakage is about of level of 10 strands in a brush session, which I do not do every day. Some might break in the shower during washing (done max twice in a week) as well, but I have no knowledge of that amount. I have not been able to find any from my clothes during days - some mornings I have found one or two from my pillow. According to other information I have now found from this forum this amount should not really affect that much. I hope :D

And thanks ynne for that shared experience with henna! I hope my strands will gain strength from it :)

[BleachedBerry]

This is probably utterly stupid thing to wonder about, but - well. I bet you are smarter than me, so I will ask nonetheless.

In short, what does the claim "average growth is 0,5 inches per month" takes in account? Does hair actually grow that much, if we eliminate possible breakage from the function? Meaning, how does the average amount of shedding impacts to this claim?

Wondering, as lets say average amount of shedding is 40 hairs per day. Could be less, could be more, playing only with averages here. If there is, lets say, 100 000 hairs average, 95 % of them growing... 95 000 hairs in growth phase. By average, individual hair grows 0,04 cm per day (totals in 1,2 cm per month). In total, 95 000 hairs grow 114 000 cm per month, or 3800 cm per day. Huge amounts, when listed this way...

However, lets say you lose 40 hair per day. Lets say those hairs are 50 cm long, each one of them. Total lose would be 2000 cm per day (one again, sounds scary). Which leads the net gain to be 3800 - 2000 = 1800 per day, meaning 54 000 cm per month or ~ 0,5 cm per month. Resulting not 15 cm amount of NET growth in a year (average, 6 inch) but 6 cm instead (under 3 inch).

Yet, it seems that usually the NET growth from year to year tend to be around 12 - 15 cm, without trims. Including shedding. What am I missing? Has the average amount of shedding been included in that average amount of growth - claim?

In reality, I am very number oriented person and thus I try to solve my breakage obsession by counting (how many individual 1 - 2 inch hair I can lose a day without it completely stunting my new growth), but as I do not know the base assumptions, I could not finish - I get two very different results, and the shedding part is the key. (As without shedding even 50 little one inch long hairs in a day would not really effect that much. From the math is seems that the breakage really does not have that big of an impact, as 50 x 2,56 x 30 (days) equals only to 3840 cm (month) or 128 cm per day, which is nothing compared to average growth numbers (114 000 per month or 3800 per day).

How do I include shedding to this all?

I apoloqize if I am being an idiot :D


I don't think breakage and length retention are related to hair growth.
Hairs in the shedding phase should not affect the hair growth rate either but I am not certain about that. Only hairs in the growing phase are growing. Hairs in the resting phase will not grow while growing hairs continue to grow and they still grow after others have shed. So it would make sense to me that hairs in resting and shedding phases wouldn't not count.

As for whats average.
Say half the hairs on your head in the growing phase grow 1/8 inch per month and the other half grows 3/4. The average is 0.435 or round to 0.5 (1/2), even though none of the hairs grow at precisely 1/2 inch.

Say 100 people grow 1/4 inch in one month, and 100 people grow 3/4 in the same month this averages to just under half inch. even though none of these 200 people grew at 1/2 inch inch rate that month.

[BleachedBerry]

I don't think breakage and length retention are related to hair growth.
Hairs in the shedding phase should not affect the hair growth rate either but I am not certain about that. Only hairs in the growing phase are growing. Hairs in the resting phase will not grow while growing hairs continue to grow and they still grow after others have shed. So it would make sense to me that hairs in resting and shedding phases wouldn't not count.

As for whats average.
Say half the hairs on your head in the growing phase grow 1/8 inch per month and the other half grows 3/4. The average is 0.435 or round to 0.5 (1/2), even though none of the hairs grow at precisely 1/2 inch.

Say 100 people grow 1/4 inch in one month, and 100 people grow 3/4 in the same month this averages to just under half inch. even though none of these 200 people grew at 1/2 inch inch rate that month.


Also I would like to add that losing short 1-2 inch hairs. Are either shedding prematurely or actually breaking and not shedding.