Though a little stress can be good for you, an overabundance of it has been linked with a host of dangerous health conditions, including heart disease, headaches, stomach problems, sleep disorders and a compromised immune system, to name just a few. Stress can also have an effect on our personal appearance -- it can cause skin to break out with acne or psoriasis and trigger conditions like telogen effluvium or alopecia areata, both of which cause chunks of hair to fall out.

But can stress turn hair gray faster, as an old wives' tale would have you believe? Onlookers were shocked when Marie Antoinette showed up for her date with the guillotine with gray hair; it was believed that her hair color changed overnight as she stressed about her fate. Every U.S. president in recent times has been subjected to a before-and-after treatment purporting to show how the world's most stressful job can take its toll.

In the case of the French queen, the sudden graying was likely due to wig removal or lack of access to hair dye. And since current U.S. President Barack Obama's barber swears that the president has never used hair dye, it's more likely that we're seeing the signs of normal aging; about 50 percent of 50-year-olds are halfway on their way to gray [source: Parker-Pope]. Gray hairs usually start appearing between the ages of 30 and 35, but the rate of graying differs according to factors like race (white people tend to go gray before Asian or black people).

Since stress causes hair loss, it's possible that losing some pigmented hair can make those gray hairs more noticeable. In this article, however, we're interested in whether stress can cause a hair to grow out from the root as gray or white. Before we get delve into some current theories on this process, let's review why our hair has color at all.

Our heads contain hundreds of thousands of follicles, and each follicle is charged with producing one hair. Cells known as keratinocytes build the keratin that becomes our hair (our skin and fingernails are also composed of keratin). Before hair emerges from the follicle, though, other cells known as melanocytes inject a pigment called melanin into the keratin. When our hair turns gray, it's due to lowered amounts of melanin, and when hair is completely white, our hair lacks melanin altogether. But why do our cells stop producing melanin as we age? And should we remain in our homes at all times, free from any form of stress, to prevent the process from happening faster?