Your hair color exists because of the presence of melanin, a pigment produced by the amino acid tyrosine. Your body usually can derive tyrosine from another amino acid called phenylalanine, but if you lack the latter, you must obtain tyrosine from your diet. While lack of tyrosine does play a role in graying hair, the full underlying causes are more complicated than just that.

The enzyme tyrosinase turns the amino acid tyrosine into melanin, which is a pigment. Melanin then enters keratinocytes -- the cells that make up your hair -- creating color. In a simple sense, less tyrosine means less melanin and thus decreasing color, or grayness.

But the underlying mechanism of graying hair is more complicated than a simple lack of tyrosine. Over time, your hair develops a large supply of hydrogen peroxide, according to the July 2009 issue of “The Journal of the Federation of American Societies for Experimental Biology.” As any hairdresser can tell you, hydrogen peroxide has a bleaching effect on hair. The study's authors conclude that hair turns gray due to the bleaching effect of hydrogen peroxide.

The progression from hydrogen-peroxide buildup to gray hair has several steps, according to ScienceDaily's 2009 review of the journal article. The process starts with a decrease in the enzyme catalase, which under normal conditions breaks down hydrogen peroxide into its harmless components. As a result of the catalase decrease, a corresponding increase in hydrogen peroxide occurs. Next a decrease in two other enzymes makes it difficult for the hair follicle to repair the damage caused by the hydrogen peroxide.

The end result of all these changes is the disruption of the normal formation of tyrosine and, consequently, melanin. That’s why simply increasing the amount of tyrosine in your diet won’t have an effect on gray hair. Instead, the underlying cause is genetic and is nothing more than a harmless side effect of a long life, according to a 2009 interview of the journal’s editor published by FoxNews.com.