Welcome to brain Stuff from How Stuff Works. Hi, I'm Lauren bulk Bam, and today's episode is another brain Stuff classic. If you've ever wondered how different types of hair dye can color your hair temporarily or permanently, our former host, Christian Sagar, how's the answer for you, 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 core text. It's just where you find the pigmented melanin proteins that give hair its color. Protecting the cortex is hair's outermost layer, the uticle. And this is hair's armor, made up of overlapping scales.
Temporary die 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 us 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 developers 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 resist fading through multiple washes.
It's trapped beneath the cuticle. Today's episode was pretty by Tyler Klang and written by me for Brainstuff YouTube series. I'm supposed to remind you to contain yourself in a brain Stuff themed T shirt available from t public dot com, slash brain stuff, and of course, for more on this and lots of other colorful topics, visit our home planet, how stuff works dot com