Saturday, May 15, 2010

Chemistry of your hair: Follicles & growth cycles

The shape of our follicles and the growth cycles determine the shape and length of your hair.

Our hair growth is a cycle that depends on the season, your age, and your type of hair. We have about 150,000 hairs on our scalps - about the same for men and women - and our hair grows about 0.3 to 0.5 mm per day or 1 cm per month (or 12 cm/5 inches per year). We lose between 40 to 180 hairs per day, with most people falling into the 40 to 80 range.

The anagen phase: The hair growth stage. This can be a cycle of 3 to 5 years, and up to 7 years or longer for some lucky people! This phase determines how long your hair will be - the longer the phase, the longer you can grow your hair. The definition of this phase is "when the follicle produces a hair".

If your hair has a 3 year cycle, your maximum length will be 36 cm or 15 inches. For a 5 year cycle, you might see up to 60 cm or 24 inches. For a 7 year cycle, you might see lengths of 84 cm or 35 inches! 

The catagen phase: The hair moves from underneath our skin to the surface. Effectively, the hair strand is squeezed upwards and rests near the opening of the sebaceous duct. It will stay there until it sheds.

The telogen phase: The hair rests for two to four months with no growth, then it is shed. The follicle then enters the anagen phase and the process starts again!

These three stages are independent in each hair follicle. You generally have about 85% of your hair in the anagen (growing) phase, about 12% in telogen (shedding) phase, and 1% in the catagen (squeezing and resting) phase. You might find a number of follicles in one phase all at once during the initial growth of hair (after hair removal or pregnancy) or during re-growth (after chemotherapy).

As a note, hair does not grow back thicker or faster when you remove it! It only seems to come back faster because we are paying attention to it and, if it's a large area, because it feels spiky. 

When your hair is growing, the shape and size of the follicle determines the shape and thickness of your hair. If you have straight, thick hair, odds are you have a large circular follicle opening. If you have very curly hair, you probably have an elliptical opening. There's nothing you can do about this but sigh and wish you had the other kind of hair (because all straight haired girls want curly hair and vice versa!).

I know some of us started off life as straight haired girls and went curly at some point naturally. What happened there?


Join me in the next post to explore this question!

4 comments:

Madeaj said...

Hello Susan

I have a question. The last year I've began looking more closely at the ingredients of the products before I buy. One item I have noticed in a lot of products is Mineral Oil. Some people on the hair forums swear that Mineral is bad for skin and hair. Then other places I see that its not bad, but it just doesn't have any value other then as a filler.

So far I try to avoid the products with mineral oil as the top ingredients because they don't work so well on my skin. Do you know why companies use so much mineral oil and does it have any benefits in hair and skin products other than filler?

Susan Barclay-Nichols said...

Hi Madeaj! Okay, here are my ideas on mineral oil - please let me know if there's more I can post (links, etc.)

Mineral oil isn't bad or carcinogenic. It doesn't offer all the fatty acids and phytosterols the natural type oils offer, but it is a good moisturizer. It doesn't sink into your skin and will form an occlusive layer that can trap in moisture and other ingredients. This can be a real benefit for very oily skin that will break out from natural oils (like mine) to offer moisturizing and occlusion from the elements.

Mineral oil has a very very long shelf, which is one of the reasons the big companies use it. Can you imagine if they were making body wash with grapeseed oil? It'd have to be bought and used within 3 months, and most consumers don't read best before dates.

My friend's mother has had the same lotion in the cabin since at least 1994. The only reason I haven't thrown it out for her is the curiosity about how much longer it will sit there before the bottle melts into a gooey mess! Yep, I'm a science geek!

Because of this incredibly long shelf life, you can leave out those anti-oxidants and other ingredients meant to keep the oil from going rancid.

It's easy to predict how mineral oil will react in a product. Natural oils - let's say olive oil - can vary in their fatty acid content, so one time you might have more linoleic acid, which means it has a shorter shelf life or may have more stearic acid, which means it'll be thicker than the last batch you used. Mineral oil is the same every time, so you know how your product will react to this ingredient.

Mineral oil can come in different viscosities, which means that you can get anything between a very thin to very thick oil that can be used in a variety of products. This is a very valuable asset because they formulators can tweak a recipe easily by substituting a thicker mineral oil to make something more moisturizing and call it a very moisturizing body wash or use a thinner oil to make a kinda moisturizing body wash without having to seriously re-formulate their recipe.

Finally, mineral oil is much less expensive than most - if not all - other oils! And because you can leave out those anti-oxidants, it's cheaper still!

These are the reasons the big companies use it (I'm sure there are many more, but this comment is already too long!). It does have some benefits like moisturizing your skin and hair and leaving an occlusive layer, but it doesn't contain the goodies we like in natural oils. As I mentioned, I have used mineral oil in my oily skin facial moisturizers because it doesn't make me break out like some of the other oils, and it does make a good basic massage oil I can keep around the house for a very long time. I don't use it often as I really do like the benefits offered by the phytosterols, polyphenols, vitamins, and so on in things like rice bran or sunflower oil.

niki (again) said...

Question: how do you explain the floor sweeping hair of crystal gayle, or the waist length locks of my cousins from Thailand? It's WAAAAy more than 35 inches of hair, and it they cut it off, it's MUCH longer than 6 inches in MUCH less than a year. My sister's daughter and my aunt's daughter (both Black, not Thai)are both 14. One has hair down her back, the other, not quite shoulder length. Neither cut significantly, or chemically processed. But....

Susan Barclay-Nichols said...

Hi Niki. I don't need to explain those lengths because they are possible within the model I explain in the post. Some hair will grow longer for more time, some will have shorter grow times. Some will be slightly faster, some will be slightly slower. Explain why my hair is beyond my waist, but my husband can't get his to the middle of his back. It's all about growing cycles. I didn't make up this model - it's an accepted biological model that you can find in any textbook on hair or cosmetic chemistry. I encourage you to Google the topic and you'll find that I'm not the person who came up with this, and that it's based on solid science.

One exception doesn't make a rule. For every Crystal Gayle, there are thousands of women who can't get their hair beyond the middle of their backs. I think if you measured your cousin's hair every single month, I doubt it's growing more than an inch a month and is more likely growing 0.4 to 0.5 inches a month. I'm not making these numbers up - they come from reputable studies and sources. Again, there will be exceptions, but I think if you do your own research on the topic, you'll see that what I'm quoting is pretty much accepted as fact.

There seems to be this bizarre one upsmanship about how quickly our hair grows. I see this in my group of friends and my youth group. I'm not sure why it's a badge of pride because it's not like you can control it!

And as someone who is seriously hair obsessed, I remember wanting to be Crystal Gayle so badly as a child. But she is definitely an exception. How many other women can you name with that kind of hair?