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Interviewer: The woman's body and mind are complex. What's hormonal and what isn't? Find out now. This is "Am I Normal?" with Dr. Kirtly Jones, the expert, on All Things Woman.

Announcer: Questions every woman wonders about here health, body, and mind. This is "Am I Normal?" on The Scope.
Dr. Jones, I'm sure so many women out there have this problem, because I have this problem. My hair grows fine when short, and then it gets to a certain length and then it just never grows anymore. Is that a problem?

Dr. Kirtly Jones: Well, it's actually not a problem.

Interviewer: It's not a problem?

Dr. Kirtly Jones: It's a problem for you.

Interviewer: Yes.

Dr. Kirtly Jones: So women and hair; women believe that hair is a secondary sex characteristic. We think of breasts as being a secondary sex characteristic. But women's skin and their hair they treat and feel as if it's important for their femininity. We share roots with the primates who are hairy all over. So what happened?

Well we lost hair on our body, at least girls did mostly. We saved hair in our pubic area and axillary area to catch scents that tell others what we're doing hormonally. And we grew hair on our head. Now how long your hair grows depends on your ethnic background, your age, and your health. Hair grows in cycles. There is the anagen phase, and this is where the hair follicle is actually pushing out new hair and making hair grow longer. There's the catagen phase where the follicle, the base, is actually dying, but a new little follicle is growing and it's going to push out the old hair.

And then there's the telogen phase, which is where the hair falls out. Now part of your body, like your eyelashes and your eyebrows, have a shorter anagen phase. So thank goodness your eyebrow hair has a short growing phase before it falls out. Otherwise your eyebrows would be as long as your head hair.

Interviewer: No, that's not good.

Dr. Kirtly Jones: No, not good. And the same thing I would say for our pubic and axillary hair. That would be kind of weird.

Interviewer: Just a little bit.

Dr. Kirtly Jones: A little bit weird. Some people's anagens are shorter, which means when their hair gets to be a foot long it just isn't going to grow anymore, and new hair grows in. So it pushes out the old hair, and new hairs start growing, and then...

Interviewer: Then you lose hair?

Dr. Kirtly Jones: That's why you lose hair.

Interviewer: Okay.

Dr. Kirtly Jones: So pushing the hair out, where the hair falls out, is called telogen; there are times in a woman's life where she loses a bunch of hair at once, and pregnancy, of course is the most famous. It's called this lovely word, telogen effluvium.

Interviewer: That sounds beautiful.

Dr. Kirtly Jones: Isn't it a lovely name? And that's where the hair is synchronized in pregnancy and when the hormones go away it's synchronized in telogen so a bunch of hair falls out. So luckily the stage that each hair follicle is in is a little different. So that way we're using and losing about 100 follicles a day. So when people say, oh my gosh, I lose so much hair. If they wanted to, if they brushed their hair, and collected all of them and counted them, somewhere between 50 and 500 is pretty normal.

Interviewer: That's normal?

Dr. Kirtly Jones: Yeah.

Interviewer: And so you lose that much, but then you grow...

Dr. Kirtly Jones: Then you're growing a new one.

Interviewer: But it seems it take forever for that to grow that long.

Dr. Kirtly Jones: It does. Being sick, being chronically ill, being malnourished of course is a big one. Being hypothyroid, meaning low on thyroid, being vitamin and nutrient deficient, all can be associated with hair loss and poor hair growth.

So how long your hair grows is a function of your anagen. Can you do anything? Are there any potions or products?

Interviewer: You're just asking all the questions for me.

Dr. Kirtly Jones: The answer is no.

Interviewer: Okay, I can't do anything?

Dr. Kirtly Jones: No. Of course if you dye or bleach, or sun damage your hair...

Interviewer: That's a different story.

Dr. Kirtly Jones: That means your hair can break, and so the longer it's out the more it's damaged. But in fact there isn't a whole lot that you can change how long your telogen is. Is it two years, is it three years, is it ten years before your hair drops out? You do want to make sure that you have a diet that's rich in omega 3 fats, vitamin D, zinc, and biotin. These are the ones that if you go to the health food store they sometimes have pills which are specifically geared with vitamins for hair and nails. So it's important to eat a balance diet.

If your hair is falling out and is getting very thin, it's worthwhile seeing a dermatologist, see your primary care doctor first, to make sure that you're not sick, that your thyroid is okay.

And then it's important if maybe you're losing it in patches, if you're losing it and getting bald patches to see a dermatologist.

Interviewer: I've heard the rumor that if you trim your hair often your hair grows back faster. Is that right or wrong?

Dr. Kirtly Jones: That's wrong.

Interviewer: That's wrong. Why is that?

Dr. Kirtly Jones: It just looks like it's growing faster. So when you've had a buzz cut, then an inch, which you might grow an inch in a month or two, looks like a lot, because you're starting from zero to an inch.

Interviewer: Right.

Dr. Kirtly Jones: When your hair is already two feet long, the inch you may not notice. So what happens at the follicle inside your skin has nothing to do with what happens at the end.

Interviewer: I would assume so, but just something I'm not familiar with.

Dr. Kirtly Jones: My mother told me that if I shaved my legs when I was 13, that my hair would grow faster, and that I would have to shave more. And the answer is not exactly.

Interviewer: My mother told me the same thing.

Dr. Kirtly Jones: Yeah, yeah, our mothers just didn't want us taking razors to ourselves when we were 12.

Interviewer: And another myth is about air drying and heat drying.

Dr. Kirtly Jones: It does dry out the hair. So once the hair has come out of your skin, it can't really change anymore.

Interviewer: Okay.

Dr. Kirtly Jones: So you do want to protect it, so anything which might damage it, which includes sunshine, UV light, some chemicals, dyeing, and drying may make the hair more fragile so it breaks off more easily. And the longer it's been around, meaning the longer your telogen, the longer the ends have a chance to break.

Interviewer: I've also heard that when let your hair flow down it grows faster, rather than when you put it up in a bun or something. Is that bogus, too?

Dr. Kirtly Jones: Yeah, that's bogus, too.

Interviewer: Where can all these bogus facts...

Dr. Kirtly Jones: Because in fact once the hair comes out it doesn't know how long it is, really. Having said that, there is something called traction alopecia. That means if you put it up in a bun and pull it really tight, then you're pulling on the little root. So if your bun is very smooth and very tight, or if you're doing braiding and pulling very tight, you can be pulling the hair out by the roots. We like tight buns, but not like that kind of bun.

Interviewer: Gotcha, okay.

Dr. Kirtly Jones: So take good care of your hair, by taking good care of your body. Stress isn't good for your hair. Acute, bad stress isn't good for your hair either, so take care of your mind. If you're noticing that your hair is growing bald in patches, see a dermatologist. If it seems to all fall out at once, and you just had a baby, good news; it'll come back.

And your hair will never be as thick as it was when you were 20.

Announcer: We're your daily dose of science, conversation, medicine; this is The Scope from the Â鶹ѧÉú¾«Æ·°æ Sciences Radio.