For most, one of the first signs of aging is graying hair. Why is that? What makes our hair go gray?
How Does Hair Grow?
One of the defining characteristics of mammals (including humans) is the production of hair.
Human skin produces hair everywhere other than the palms of our hands, the soles of our feet, and our lips.
Each hair grows from a follicle located in the skin. We are each born with about five million hair follicles.
I like this diagram because it helps me explain several things about hair growth.
Each hair follicle has its own blood supply (the dermal papilla). This blood supply brings nutrients to, removes waste from, and allows gas exchange (oxygen and carbon dioxide) in the cells that produce hair.
A sebaceous gland supplies oil to the hair follicle and is what gives hair its shine. It is also the reason why hair can become oily if not regularly washed.
Also, each hair follicle is associated with a tiny muscle—the arrector pili (or erector pili) muscle. When this little muscle is stimulated (by cold temperatures or in response to stress), it causes the hair to stand on end causing what is commonly called “goosebumps”.
Did you know that there was such an amazing structure at the base of every single one of your hairs?
Hair grows from the bottom, or root, of each hair follicle. Stem cells in the root produce special cells called keratinocytes. As keratinocytes continue to form from the root, the first keratinocytes are pushed up through the follicle. Eventually, the keratinocytes die leaving behind a protein called keratin—the major component of hair. (Keratin is also the major component of fingernails). As this process continues, the hair is pushed from the skin.
You may have noticed that the hair on your body grows at different rates and to different lengths. Thankfully, the hairs on our arms and legs don’t grow as quickly nor as long as the hairs on our scalp. That’s because each and every hair follicle has a cycle of growing. This video does a great job at explaining the process.
How Does Hair Get its Color?
Keratin—the main component of hair—is nearly colorless on its own. Our hair gets its color from the pigment melanin—the same pigment that gives us our skin and eye color.
Melanin is produced from special cells called melanocytes which are found at the root of each hair follicle. Melanocytes produce melanin and transport it to the keratinocytes—the cells that are responsible for forming hair. The keratinocytes become pigmented and when they die, so is the keratin they leave behind.
(Interestingly, there are two types of melanin associated with hair color. Eumelanin is dark brown or black while pheomelanin is reddish yellow. The amount of each type of melanin your body produces gives you your particular hair color. What determines which type of melanin your body produces? Your genes, of course!)
Why Does Our Hair Turn Gray as We Age?
Most scientists believe that our hair grays as we age because the melanocytes that supply each hair with color eventually wear out.
Gray hair is produced as melanocytes start to decrease the amount of melanin they add to the hair as it is growing.
When hair is produced from follicles with no melanin produced at all, white hair is formed.
When I got my first gray hair, I pulled it out. That worked for a while…until the grays kept coming. Now I, like many, depend on my hairstylist to keep the grays at bay. Still, they don’t bother me as much as they used to. My gray hairs are like battle scars, and remind me of all that I’ve been through. Aging is rough, but I’ll take it. It’s better than the alternative.
Students learn all about hair as they study the Integumentary System in my online high school anatomy and physiology class. This class is fun, engaging, and informative with lots of opportunities for hands-on exploration. To learn more about what we study and how the class is organized, visit: High School Science Classes Taught by Dr. Kristin Moon