Long before I ever thought about doing hair, I was intrigued by the chemistry behind it.  I remember wondering to myself, “how does hair dye work?” almost every time I would get my hair done.  I mean, it made no sense to me.  You put something on your hair and it changes the color to whatever you want.  Is it magic? There has to be a reasonable explanation, right?  Well, it’s actually quite simple….

Have you ever wondered to yourself, "How does hair dye work"? Well, the first thing you should know about hair color is...

Anatomy of Hair:

Have you ever wondered to yourself, "How does hair dye work"? Well, the first thing you should know about hair color is...

First things first:  I need to explain to you about the anatomy of the hair shaft.  It is important information to understand the rest of the article.  I also provided an image of a cross-section of a hair shaft to better illustrate how things look up in there.

The Cuticle:

You probably hear about the cuticle more than anything else.  The cuticle is the protective outer layer of the hair shaft and it’s composed of dead cells, overlapping each other in layers.  Its function is to protect the inside of the hair shaft, but it also plays a large role in how healthy your hair is.  For example, when the scales lay flat, your hair will appear to be smoother and more healthy, and vice versa.  When they are raised, your hair will be rough and coarse.

The Cortex:

The cortex is the money spot when talking about hair color.  It is found between the cuticle and medulla and holds all of the natural (and unnatural) pigment, which gives hair its color.  The natural pigment in the cortex is called “melanin,” which is also what gives skin its color.  It is also important to note that the melanin is denser near the cuticle than it is towards the middle of the hair shaft.

The Medulla:

This is the central core of the hair.  This nearly invisible section serves as the “marrow” of the hair and is the softest part of the hair shaft.  Although scientists do not know the exact purpose of the medulla, they speculate that it is more prominent in gray hair.  Last but not least, it contains large amounts of mitochondrial DNA, which is passed from the mother to her offspring (Wikipedia).  Unfortunately, none of this is important to how hair dye works.

That’s Great… But How Does Hair Dye Work?

I promise all that sciencey stuff is important, but now that you have some background on hair anatomy, let me get to the good stuff….

Types of Hair Dye:

Now is a good time to let you know that there are a few different types of hair dye, and they all work differently.  To answer the question, “How does hair dye work?” we need to first distinguish what type of hair dye we are talking about.

Temporary Hair Dye:

Temporary color will temporarily color your hair, without the long-term commitment.  The next time you wash your hair, it should rinse completely out (unless your hair is very damaged and porous, in which case, it might take a couple washes).  It comes in a bunch of different forms like rinses, chalks, sprays and more.  Colors like this work by simply coating the hair shaft with color (it does not chemically change to the hair).  When you wash your hair, it should rinse right off.

Semi-Permanent Hair Dye:

Semi-Permanent hair dye is one step more permanent than temporary.  It will stay in your hair for a little while but will wash out eventually.  An example of semi-permanent color is Manic Panic, and although it is usually associated with punky, unnatural colors, it can come in natural colors as well.  Many people prefer this type of hair dye, since it will not damage the hair, and it lets you try a color out before you commit to it.  The color should last about 16-24 shampoos before completely fading out, but it will fade a little each time you wash your hair.  The unfortunate thing is that you cannot go lighter with semi-permanent color; you must choose a shade darker or the same level for it to be noticeable.

This type of hair dye is made of some large and some small color molecules.  Most of them adhere to the outside of the hair shaft, while some of the smaller ones will penetrate into the cortex, depending on how porous the hair is.  This is why bleaching the hair first will sometimes hold the color better.  Bleach will open up the cuticle, allowing more color molecules to get inside.

Demi-Permanent Hair Dye:

Next, we should talk about demi-permanent hair dye.  It still does not permanently change your hair color, but it will last longer than semi-permanent color.  There are a few differences between demi-permanent and semi-permanent color:

  1. Demi-permanent color uses developer (I will explain that in a bit)
  2. It lasts longer than semi-permanent color
  3. It is not usually associated with punky, unnatural colors

So, I mentioned that demi-permanent color uses developer, unlike temporary or semi-permanent color.  Developer is the oxidizing agent you mix with color (usually peroxide).  Different volumes of developer do different things, but demi-permanent color uses a weaker volume, which only allows the color to deposit.  I know that probably sounds confusing, so let me explain a little better….

The oxidizing agent in the developer forces the scales of the cuticle to open.  When the cuticle opens, color molecules are able to get inside the cortex with the natural melanin molecules.  The cuticle closes back down, trapping the color molecules inside.  Demi-permanent color should last about six weeks but should fade out completely before leaving you outgrowth.

Permanent Hair Dye:

Permanent hair color works similar to demi-permanent except it should last forever.  However, some colors, like red, have smaller molecules that will leave the hair shaft faster, making the color fade over time.  Additionally, the polymers that make the red color are easily broken down by UV light and other forms of oxidation, allowing the molecules to escape.

The other difference between permanent hair dye and demi-permanent is that you can go lighter shades with permanent color (on virgin hair… see the Golden Rule of Hair Color).  What this means is, if your natural color (not hair that has been previously dyed) is a dark brown, you can lift it to a medium brown/dark blonde without bleaching it first.  How high you can lift your hair depends on how dark it is to start with, and what developer you use with the color.

Volumes of Developer

If you have a level 5 brown hair color, and you want to lift it to a level 9 blonde, you would want to use 40v developer for four levels of lift.  Let’s say you wanted to lift your hair 3 levels, you would want to use a 30v developer.  If you wanted to lift it two levels, you should use 20v (additionally, 20v is what you would want to use to cover grey hair).  If you wanted to go the same level or darker, you would want to use a 10v.  There are also high-lift blondes that require you to use a higher developer (or double 40v) to drastically lighten your hair.

Do you know what that letter / number combination on the hair color box means? Learn how to read hair color numbers / labels like a professional!

Now I should mention that if your hair already has dye on it, you will need to lighten your hair or strip the color first before using color on your hair.  Using hair color on previously colored hair will not lift the color out of it.

Your Turn:  Did you enjoy this post?  I’ll love you forever if you share it with your friends on your favorite social media website!

Did you learn anything new today?  Do you have any further hair dye questions?  I’d love to read your feedback in the comments section below…

1 Comment on How Does Hair Dye Work? The Interesting Science Behind It…

  1. Cassie
    August 1, 2017 at 7:21 PM (3 months ago)

    Thank you so much for sharing! This was very insightful as I used to dye my hair with box dye and my hair has been forever destroyed by it! Interesting to learn about how Dye works.

    Reply

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