Some see gray hair as a sign of wisdom. But it isn't a head full of knowledge that gives hair a silvery sheen. Graying is a natural part of aging, and multiple factors weigh into when and how quickly a person goes gray. Old age isn't a prerequisite, either. Hair can turn gray prematurely.
Melanin
Although different conditions and circumstances contribute to the development of gray hair, they all have something to do with a naturally occurring enzyme called melanin. Melanin is the pigment that gives color to hair, skin and eyes, according to Popular Science. There are two types of melanin. Eumalinin contributes darker shades to hair color, and pheomelanin contributes lighter shades. These combine in varying degrees to give each person a distinct hair color. Melanin is produced separately for each individual hair follicle, and with time and age, melanin production starts to decline. A gray hair is a sign that melanin production is waning in that follicle, and when the hair turns white, melanin production has ceased.
Genetic Factors
A person's natural hair color is determined by his genetic profile, and similarly, so is the time when hair follicles begin producing less melanin, according to a 2005 report by the Journal of Investigative Dermatology. Dr. Karin U. Schallreuter, professor of clinical and experimental dermatology at England's University of Bradford, says in a New York Times article that genetics can make someone more or less susceptible to graying. This can contribute to both premature graying and latent graying.
Hydrogen Peroxide
In February of 2009, European researchers discovered clues as to how graying could be related to naturally occurring hydrogen peroxide levels, according to the New York Times. The researchers were investigating a genetic skin condition called vitiligo, which causes patches of skin to have no pigment. When it was discovered that vitiligo was associated with diminished activity of catalase, an enzyme that breaks down hydrogen peroxide in the body, the researchers theorized that graying could be the result of excess hydrogen peroxide in hair follicles. All follicles produce small amounts of hydrogen peroxide, but these trace amounts accumulate over many years, eventually building to a concentration that can disrupt the normal synthesis of melanin. This process is described as hairs bleaching themselves from the inside out.
Ethnicity
Though gray hair affects people of all ethnicities, it does not do so uniformly. According to the New York Times, white people are susceptible to graying at the earliest age. Asian people tend to begin going gray a few years later, and black people typically go the longest before getting gray hair.
Vitamin B12 Deficiency
A medical study published by the National Institutes of Health describes an 11-year-old boy who had premature gray hair, as well as hyperpigmented skin, anemia and recurring aphthous ulcers. After a difficult diagnostic period, physicians discovered that the symptoms were related to a deficiency of vitamin B12. The boy's hair resumed a normal shade after vitamin B12 replacement therapy.
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