When my daughter asked me why people get grey hair, my immediate response was, of course, that kids cause it. Later, I looked into the question a little more scientifically, but the answer was not black and white.
Each hair is produced in a tear-shaped pit called a follicle. Keratinocytes are cells that produce the protein keratin that form the hair, while melanocytes are cells at the base of the follicle that inject melanin pigment into each hair. Melanin comes in two types—the darker shade, eumelanin and the lighter shade, phaeomelanin. These blend to form the different hair colours. If less melanin is injected, the hair becomes paler. If no melanin is present, the hair will be white. This whitening is called canities. If you have some white hairs and some darker hairs, the overall effect can be grey, which may or may not come in fifty shades.
Hairs go through a cycle of growing and then falling out. To generate a new hair, a new set of production cells, including melanocytes, is created from stem cells. Eventually, the new melanocytes do not work as well. We usually associate age with going grey and the chance of going grey goes up 10–20% for each decade that you age after thirty. But why this occurs is still not clear. Other internal factors that affect the greying process include genetics (probably the most significant), hormones and where on the body the hair is. External factors include climate, pollutants, toxins and chemical exposure, which may damage the stem cells that produce melanocytes. This may have to do with a protein called Wnt, which acts as a signal to melanocytes to produce hair colour. If this protein is lacking, then the melanocytes stop producing colour.
To bleach his own
Now, there is the possibility that your melanocytes might still be working, but the pigment they produce is getting bleached out. Scientists studying vitiligo, a skin disease that results in a loss of inherited skin and hair colour, found that the loss of colour is related to a buildup of hydrogen peroxide. Hydrogen peroxide is made up of two hydrogen atoms and two oxygen atoms and breaks down into water and oxygen when it reacts, which is why you see bubbling when you put some on a scraped knee. Some people remove colour from their hair on purpose with hydrogen peroxide (bleaching). When scientists added an antioxidant to bleached hair, which reacted with the hydrogen peroxide, the colour returned. The buildup of hydrogen peroxide may also occur in people as they age.
It's not clear if kids or other sources of stress affect melanocyte behaviour or the buildup of hydrogen peroxide, but my darling daughter does seem to affect the rate at which I pull my hair out.