I was just wondering... how long for all the hairs on your head to be replaced?

[linda g]

I was just wondering about hair turnover!

Does anyone know, in general, how long it would take for every hair on your head to be shed and be replaced by a new hair?

I have a feeling that this is related to the idea of terminal length, so this could be a matter of years, right?

[GRU]

I don't recall where I heard it (anatomy class, maybe?), but I think the typical hair "lives" about seven years before being shed. Those with a longer-than-normal terminal length probably have hairs that "live" 8-9-10 years, while those with shorter t.l.s are probably in the 4-5-6 year range (resulting in an average of about 7 years).

[Barniie]

well if you lose 100 hairs a day (yikes!) then you just get the amount of hairs on your head (100,000 avg, more for blondes, less for reds) so you get... 1000 days. So about... 2.8 years. xD

ETA: Wow i thought i might be more than that, probably is!

[linda g]

Very interesting... so theoretically, even if I did no trimming, I could expect for all dyed hairs to be gone from my head in 7 years!

[EdG]

The time is given by terminal length divided by growth rate.

For me:

(54 inches) / (6.5 inches per year) = 8.3 years :)

Ed

[spidermom]

I have also heard that the average life of a single hair is about 7 years, which absolutely does play into terminal length. If a hair grows 1/2 inch per month for 7 years, the hair will be 42 inches long when it reaches terminal length and sheds out.

Different hairs on the same head grow for different periods of time, however. I regularly see hairs as short as 2-4 inches long on the bathroom counter or in the sink, and I know they are naturally shed hairs because one end will have a little root bulb and the other end will be pointy.

Xandergrammy stopped dyeing her hair and has been letting it grow without trimming, so I've been watching her photos to see how long it takes before all the dye is gone.

[HairColoredHair]

If my current length is terminal (Forbid the thought) and I grow about 6 inches a year... probably 8 years.

Can't measure the hair the LHC way, after all. :)

[trolleypup]

For the purposes of this question, the shorter terminal length hairs in you scalp don't matter, since they shed out faster. If you are at terminal, and you know your regular growth rate, finding the longest shed hair will give you the maximum hair age and the time of a complete turnover.

For me, 1/2 inch per month. My longest shed hair was 43 inches, for 7 years and 2 months. The vast majority of "long" sheds are 42 inches or less, so the general turnover age is probably closer to 7 years.

[Igor]

Stolen from my blog... :wink:


I don’t know exactly how many hairs I have on my head (Guestimate here 140.000)
Some hairs have a longer growth cycle than others
Breakage and trims are not included


365 days with circa 40 lost hairs per day means 14.600 hairs per year
140.000 divided by 14.600 means it will take me circa 9,6 years to have replaced all the hairs on my head (terminal)
A years worth of growth is circa 18 cm / 7,5 inches
It means my hair will circa be able to grow 173 cm / 68 inches

365 days with circa 50 lost hairs per day means 18.250 hairs per year
140.000 divided by 18.250 means it will take me circa 7,6 years to have replaced all the hairs on my head (terminal)
A years worth of growth is circa 18 cm / 7,5 inches
It means my hair will circa be able to grow to 145 cm / 57 inches

365 days with circa 60 lost hairs per day means 21.900 hairs per year
140.000 divided by 21.900 means it will take me circa 6,4 years to have replaced all the hairs on my head (terminal)
A years worth of growth is circa 18 cm / 7,5 inches
It means my hair will circa be able to grow to 115 cm / 45 inches

Look at the difference just 10 or 20 hairs make! :shocked:

[linda g]

Thanks for indulging my curiosity, everyone :)

I, too, will be watching Xandergrammy with interest. ;) I still haven't made a final decision about whether to continue to microtrim the henna out of my hair, or to just let nature take its course, so to speak.