Re: Does heat and/ or humidity affect the rate of hair growth?

Hi Steve,
     Interesting question,one to which I don't have a very good answer.  I 
have done a search of a medical database called Medline to see if any 
research has been done on moisture or heat affect on human hair growth, and 
unfortunateky nothing came back.  So I guess I'll have to suppose about the 
answer, but before I do, I'll say that perhaps the best person to ask would 
be a dermatologist.  Since hair follicles are located in the skin, and that 
is their specialty area, what better person to ask.
     But here is my answer.  Hair follicles are located in the middle layer 
of skin called the dermis.  You can think of the follicle like a pit in the 
skin from which the hair grows from the root.  Actually the root itself is 
made of cells that produce the proteins that make hair.  Also, pigment 
producing cells, like those of the skin, contribute pigments to the hair 
that give it a particular color.
     Hair growth occurs as a 3 stage cycle composed of active growth, 
retraction-when the follicle starts to slow down, and rest-no active 
growth.  Most follicles are in active growth over 90% of the scalp, and the 
other 10% at rest.  From what I have read, the factors that affect these 
stages are general scalp health like blood supply, or damage to the 
scalp(which heat can definitely do).  In other species of mammals, hair 
growth occurs in wave like patters from head to toe, but in humans the 
stage of hair growth varies from follicle to follicle.  I guess that is why 
most animals don't have to get regular haircuts.
     The average rate of hair growth in humans is figured to be about 
0.35mm a day, but this varies upon gender and age(women are faster than 
men and adolescents fater than adults).  The longest term of active growth 
is from 6-10 years, with 14-21 days of retraction, and 30-90 days at rest 
before returning to active growth.  The old fiber is usually pushed out by 
the new fiber.  Hair follicle cycles of growth may occur throught ones 
life, but damage to the hair follicle such as heat, trauma, UV radiation 
can end this process altogether.  
    So, as far a heat and moisture playing a role in increasing the rate of 
hair growth, I would have to say it has no effect.  The body does a pretty 
good job of maintaining a consistent temperature to allow normal cell 
functions.  Even when it is hot outside, we sweat to get rid of excess heat 
so that we maintain our optimum temperature.  So I think heat is out.  As 
for moisture, I doubt that too.  We constantly produce moisture from the 
skin which is composed of water and oils.  These are normal excretions for 
keeping the skin protected from overly hot, cold, dry or wet conditions.  
It doesn't seem likely that moisture would initiate hair growth since we 
deal with it everyday.  Besides, the hair producing part of the 
skin(dermis) lies relatively far below the part of the skin where the 
moisture would be(epidermis).  Oils around the hair fiber would prevent 
moisture from entering the follicle and affecting it there.  Anyway, I am 
only going off the information I have come across, and my basic 
understanding of skin and hair follicles at this point to make my 
assumption.  I still think asking a dermatologist would be your best bet.  
Sorry I didn't give you a concrete answer, but perhaps I helped a little.  

Mark Sullivan