Last week, I promised to write about hair. I had a test question I threw out having to do with hair color. So with that and questions about hair earlier in the week, let’s talk about it more…
How did I get my hair color?
Short answer is it’s in your genes, but I know you want the complete college answer!
From Wikipedia sources below, these genes control stem cells that make melanocytes, which you remember makes color in the skin. There are two types of pigment involved in hair color: eumelanin (dark brown-black) and pheomelanin (we talked about carotene, producing an orange-yellow color). The melanocytes that produce these pigments are found near the bottom of the hair follicle, the cylinder holding the hair root.
The more eumelanin your melanocytes produce, the darker your hair color. If your hair color is light enough, it might allow some orange-yellow-red color from pheomelanin to show – then you have your red hair, strawberry blonde, blondes. Good photos at Wikipedia: http://en.wikipedia.org/wiki/Human_hair_color
Gray hair arises from lack of pigment from melanocytes. You can get it early, but they say hair starts turning gray sometime between your twenties to about forty. You may become gray if you’ve got thyroid or B-12 deficiencies.
It’s normal for the amount of pigments produced to change over time. That’s why a child may start with one color hair and change to a different color. Same for turning gray.
What happens when someone turns gray is the stem cells that become melanocytes begin to die. When they die, there’s no cells to make the color pigments. Researchers have traced this event to genes Bcl2 and Bcl-W. They also think an accumulation of hydrogen peroxide may accelerate or cause these cells to die. An anti-cancer drug Imatinib has been shown to reverse the graying process. It may have to do with its effect on stem cells or blood flow.
I love seeing curly hair, but that’s probably because I have such straight hair. I know gals with curly hair who hate it. Anyway, it’s genetic, again. Curly hair has been traced as an autosomal dominant trait. It causes follicles (remember this is the tube the hair root sits in) to be either completely circular or oval. The more circular the follicle is, the straighter the hair that resides in it. Oval follicles give rise to curly hair.
I had someone ask me specifically about alopecia – also known as hair loss. While there are many causes, what happens in the body level?
Hair normally goes through 4 phases of growth: anagen (rapid growth, lasts 2-7 years), catagen (a transition taking 2-3 weeks where the hair follicle attaches to the hair shaft, causing hair to stop growing), telogen (hair begins to fall – normally we shed 50-100 hair shafts per day from our heads), and exogen (the hair actually sheds and the follicle is empty). They say you’ve met the requirements to be diagnosed with alopecia if you lose more hair than are replaced (uh, duh, you don’t have to be a doctor to know that).
Most baldness is associated with male-pattern baldness, which can account for over 95% of hair thinning and loss in men. The trigger for this is the sex hormone DHT. What happens is the follicle width decreases, something they call follicular miniaturization. The chamber that holds the hair gets smaller and smaller so it can’t produce the hair we know (called terminal hair). So without new growth, you lose hair and they aren’t replaced, and you become bald.
Researchers suspect the gene SOX21 may play a role in hair loss.
If you found this post interesting, you might also be interested in how do we get our eye color:
One more post coming…