Though hair comes in a variety of hues, there are only two types of melanin, or pigment. Eumalin is a dark brown or black pigment, while pheolmalin is reddish yellow. When the two combine in varying levels, as dictated by genetics, they produce the wide range of hair colors we all sport.
Why Hair Goes Gray
There is no direct link between stress and gray hair. Rather, if you want to figure out when you'll go gray, you need look no further than your parents, as our genes seem to have power over what comes out of each hair follicle. In recent years, though, scientists have been digging a little deeper to determine what's happening with our genes and cells when hair goes gray. Not because they want to solve the mysteries of gray hair, but rather because our hair might reveal information that's useful in treating other conditions related to aging.
In 2004, for example, researchers from the Dana-Farber Cancer Institute in Boston were studying melanoma, which involves an overproduction of melanocytes in the skin, which can lead to skin cancer. While trying to learn more about the nature of melanocytes, the researchers found that hair might go gray as the supply of melanocyte stem cells is depleted. Even before those stem cells are completely gone, though, they begin to make errors, such as depositing the pigment at the wrong place in the follicle, so that it has no effect on the hair [source: Dana-Farber Cancer Institute]. The next task for these researchers? Figuring out why the amount of melanocyte stem cells decrease when it comes to our hair while they reproduce at high levels in the skin and form cancerous tumors.
The results of a 2009 Japanese study indicated that stress did in fact cause gray hair, but not the type of stress that comes with a teenage driver or an impending job interview. Rather, researchers found that genotoxic stress, in the form of ultraviolet light and chemicals, damages our DNA and could cause the depletion of those melanocyte stem cells. Again, this finding holds promise for other conditions, as the same thing has been demonstrated to occur in blood stem cells and cardiac and skeletal muscle [source: Cell Press]. Though research seems to indicate that we could stop the DNA damage by removing the genotoxic stress, the researchers estimate that just one mammalian cell is subjected to 100,000 such stressors in one day, making complete avoidance impossible [source: Dell'Amore].
One last theory about graying hair ignores the stem cells altogether. In 2009, European researchers claimed that hair goes gray because the amount of hydrogen peroxide in our follicles builds up over time [source: Parker-Pope]. Their next step is figuring out if stress can increase these hydrogen peroxide levels or if it's driven by chemicals. Even if there is a link between the hydrogen peroxide build-up and stress, researchers caution that it all goes back to those genes from your parents. Our abilities to handle large amounts of stress may in fact be wired into our genes, meaning that where gray hair is concerned, there may be no way of escaping your genetic destiny.