Welcome to brain stuff from how stuff works. Hey, brain stuff, it's Christian Sager here. There are three basic chemical formulations of hair dye, temporary, semi permanent, and permanent. Before we look at what each of them do, let's look at the physical structure of hair. Hair is dead stuff, three layers of slightly different dead stuff. The core, called the medulla, is not pertinent to our interests today, but it's surrounded by a thick layer of cells called the cortex. And
that's no relation to your brain's cortex. It's just where you find the pigmented melanin proteins that give hair its color. Protecting the cortex is hair's outermost layer, the cuticle, and this is hair's armor, made up of overlapping scales. Temporary dye just sticks to the cuticle. It's more like paint really. It will usually circle the drain with your next shampoo. Semi permanent dye contains molecules of pigments so tiny that they can slip between the scales of the cuticle and
stick to the cortex. But it's still more paint like. It doesn't chemically react with anything in the hair. The little pigment particles will wash back out through the cuticle scales with soapy water, so a semi permanent die lasts about twelve shampoos max. Now, both temporary and semi permanent dyes can sometimes stain very light colored hair, but permanent dye, as the name suggests, is designed to stay with your
hair until the hair grows or falls out. Now there are as many formulas for permanent dye as there are proprietary brands, and in general, permanent dye consists of two solutions. First, an alkaline chemical plus two types of particles that will come together to form the new color, die precursors and die couplers. Second, the developer. This is an oxidizer, usually a weak solution of hydrogen peroxide. You or you know your salon professional mix the two together right before applying
them to your hair. The alkaline chemical, either ammonia or more gentle substitute, goes to work opening up the cuticle. For dye to be most effective, it needs to access the hair's cortex. Alkaline stuff temporarily softens and relaxes the cuticle scales. The next hurdle in achieving a new hair color is getting rid of some of the existing color. That's the melanin that's in the hair's cortex. Enter the developer.
It oxidizes the melanin molecules, breaking melanin's double carbon carbon electron bonds and giving up one of its own oxygen atoms to fill in the space. The result, the melanin turns colorless and releases sulfur atoms. That's right, part of permanent dyes characteristic stink isn't actually the die at all, but an element of your hair passing into the air. But that's not the developer's only job. It also kicks off the reaction that brings together the new color molecules
by oxidizing the die precursors. These are usually colorless chemicals that develop color when oxidized. The resulting pigmented particles, called intermediates, are monomers that, left to their own devices, would slip through the cuticle scales like semi permanent dye, But the die couplers react with the intermediates to form polymers of pigment that are too big to just slip back out, and that's how permanent color resists fading through multiple washes.
It's trapped beneath the cuticle check out the brain stuff channel on YouTube, and for more on this and thousands of other topics, visit how stuff works dot com.