When it Comes to hair color, we live in exciting times. We can darken hair for a day or a month, brighten strands permanently, even make raven-colored tresses as pale as sunlight. We can add lighter, brighter, or darker stripes, as well as cloak gray hair in the color it once was or paint strands in a kaleidoscope of candy-inspired shades. We can opt for hair color that gradually fades with time (and leaves no tell­tale roots) or color that stays with the hair strand as it grows out.

In the beauty world, enlivening or darkening your natural shade is not a big deal. Making a dramatic change, such as lightening hair, is a big deal. An easy-to-remember rule: the bigger the change, the more chemicals needed, and the more chemicals needed, the harsher the process.

How color works

Generally speaking, the more temporary a color formula is, the less damage it does to hair; the more permanent a color, the more damage it does. Also, generally speaking, the more temporary a color formula, the more subtle the change it can create, while the more permanent a color is, the more extreme the change it can produce. This has to do with chemistry. Colors that wash out in less than 12 shampoos ­ temporary and semi-permanent colors - simply coat the hair shaft; because they aren't hanging around, they don't need chemicals to push pigment molecules into the strand's cuticle layer. Hair color formulas that last longer than 12 shampoos ­ demi-permanent, permanent, and bleach - use one or two chemical elements to open the cuticle layer and force pigment molecules into the strand.

The basic chemicals

Peroxide is an ingredient in demi-permanent hair color, permanent hair color, and bleach and is used to help lift the cuticle layer so other ingredients can get into the strand and do their jobs. Peroxide also helps create longer-lasting color - in fact, the longer-lasting the color, the more peroxide a dye has.

Ammonia - or the ammonia substitute called monoethalonamine (MEA) - is found in many permanent hair colors and bleach. Ammonia dives into the strand and removes some or all of the hair's natural melanin. Why is all this necessary? Because the less natural melanin a strand has, the more readily it will accept new pigment from a hair-color formula.