The Science of How Hair colour Works print

How Haircolour Works


To understand the science of haircolour, it is important first of all to understand WHAT we are colouring. As you know, types of hair can be drastically different. From curly to straight, thin to thick and blonde to black, almost no two hair strands are alike. And knowing your hair type is very important when colouring your hair. For a basic overview of your hair’s makeup, take a look at our Hair Science article.

Once you know a bit about the makeup of your hair, it’s important to understand haircolour and how it affects your hair. Your natural hair pigment, called melanin, is housed in the cortex of your hair—which are the cells aligned along the hair fiber. This is why haircolouring also takes place in the cortex, since it affects the natural pigment of your hair.

Haircolouring works by coating each strand with colour (semi-permanent haircolour) or by penetrating each hair cuticle, entering the hair cortex and bonding with the hair (permanent haircolour). While semi-permanent haircolour can be shampooed out eventually, permanent haircolour, as the name suggests, permanently dyes the hair. However, since hair constantly grows, the colour will eventually grow out as new, uncoloured hair grows in.

Just as there are different types of hair, there are different types of haircolour, as identified in this chart.

Haircolour TypeAmount of Time Colour LastsLift Performance / Grey Coverage
Permanent haircolour
(Level 3)
Until hair grows outUp to 3 levels lift

Up to 100% grey coverage
Demi-permanent haircolour
(Level 2)
28 washesNo lift

Up to 50% grey coverage
Semi-permanent haircolour
(Level 1)
6 – 8 washesNo lift

Up to 30% gray coverage
(Level 0)
1 – 3 washes No lift
Bleaching & Highlighting Until hair grows outUp to 6 levels of lift

No grey coverage


As the name suggests, this type of haircolour permanently colours your hair. It works from the outside in, penetrating each hair cuticle, entering the hair cortex and bonding with the hair. The process involves removing some or all or your natural colour and/or adding your desired colour with the dye. While the colouring remains on your hair, your uncoloured hair at the roots will show through as your hair grows.

Here are some other facts about permanent haircolour:

  • Offers 100% grey coverage, even on resistant greys
  • Can lighten hair by 2 levels
  • Can also be used for subtle colour changes
  • Lasts longer than direct dye products
  • Root application recommended every 4 – 6 weeks to avoid noticeable roots re-growth


Semi-permanent haircolour gently adds colour molecules to the cuticle layer of your hair. Lasting for 6 – 8 washes, each wash lifts the cuticle—allowing colour to escape. It contains no ammonia or peroxide and offers no bleaching of your natural hair pigment.

Here are some other facts about semi-permanent haircolour:

  • Colour is already formed in the tube—so you don’t have to mix anything
  • It eventually washes out in 6 – 8 shampoos
  • It also contains no ammonia or peroxide


This type of haircolour works by coating each hair strand with colour. If you are dying your hair for the first time or only want to enhance your natural colour, try a demi-permanent haircolour product (lasts through 28 shampoos) that is close in shade to your current or natural haircolour.

Here are some other facts about demi-permanent haircolour:

  • Lower pH than permanent colour
  • No ammonia, uses ammonia substitute (MEA or AMP)
  • Lower peroxide concentration than permanent colour
  • Similar dye palette to permanents
  • Leaves no visible root line


Temporary haircolour only coats the surface of your hair. It remains on the surface of the hair, so it washes off quickly (usually after 1 – 3 shampoos).

  • Lower pH than permanent colour
  • Lower peroxide concentration than permanent colour
  • Limited dye palette


Bleaches and lighteners can help even dark hair go blonde.

  • High lift blonding products give up to 3 levels of lightening and provide tone
  • On-the-scalp lighteners provide up to 4 levels of lightening
  • Off-the-scalp bleaches can lighten up to 5 levels


Hair is almost constantly exposed to things that can cause damage: UV light, chlorinated water, saltwater, your diet, perms, heat styling. Even things like shampooing, towel drying and brushing cause friction, which can damage hair.

Once damaged, hair becomes rough and dull. Conditioners work to both help protect against damage and repair past trouble, leaving hair silky and shiny.

  • Conditioners smooth the cuticle to help restore smoothness
  • They can also form a protective coating to help prevent damage
  • Many conditioners also have an ingredient that helps rebuild hair’s ability to retain moisture


Your current haircolour (natural or previously coloured) makes a difference in how semi-permanent haircolour or permanent haircolour turns out. If you’re not sure what shade to choose, go with this longstanding haircolour rule: You can change your haircolour successfully up to two shades lighter or darker than your starting colour. If you currently have medium brown hair, for example, you could lighten it to a light brown or a dark blonde, or go darker to a dark brown.

Hair type also makes a difference. Coarse hairs, which are large in diameter, generally take more time to absorb colour, while fine hair, which is small in diameter, takes less time to absorb colour. Dry or permed hair may absorb colour more quickly. Since there are several factors that affect timing, it’s best to use a strand test to estimate colouring time.

Now that you know how haircolour works, it’s time to colour!