As for color, the shade of your hair is determined by natural pigments called melanins that are produced by skin cells. Surprising as it may seem, just one melanin—a black pigment called eumelanin—is responsible for most hair shades, from blond to black. The formula is simple: the greater the eumelanin level, the darker the hair. However, eumelanin cannot take credit for red hair, which owes its unique hue to a rarer, reddish type of melanin called pheomelanin. When skin cells grow old and stop producing eumelanin or pheomelanin, a person's hair turns gray or white.
Our genes determine the color and texture of our hair, but there are ways of getting around genetics. As the one-third of American women who color their hair and the half who perm or relax their locks can attest, hair chemistry can be easily changed. Perms, relaxers, dyes, shampoos, conditioners, and even curling irons and blow dryers all work their magic by tinkering with hair's normal chemical structure.
In fact, every time you wash your hair or go swimming, you generate a small chemical reaction. Hydrogen-rich water molecules snap the weak hydrogen bonds between your hair's keratin chains, prompting even the curliest of locks to straighten temporarily when wet. As the hair dries, the hydrogen bonds are reestablished, and waves or curls return.
The opposite occurs with straight hair that is dampened and then wound around pins or rollers so that different parts of the keratin chains are adjacent to one another. As the hair dries, it forms new hydrogen bonds and is temporarily transformed from straight to curly or wavy. Blow dryers, electric rollers, and curling irons act along the same principle, but use heat energy to reinforce the new bonding pattern.
But as people whose hair style depends on a curling iron or a blow dryer know, their efforts can be undone in minutes. All it takes is a little water in the form of a sprinkling of rain or a moist sea breeze to send your hair's hydrogen bonds scrambling back into their normal alignments.