The Science of How Hair Color Works print

How Hair Color Works

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To understand the science of hair color, it is important first of all to understand WHAT we are coloring. 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 coloring 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 hair color 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 hair coloring also takes place in the cortex, since it affects the natural pigment of your hair.

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

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

Hair Color TypeAmount of Time Color LastsLift Performance / Gray Coverage
Permanent hair color
(Level 3)
Until hair grows outUp to 3 levels lift

Up to 100% gray coverage
Demi-permanent hair color
(Level 2)
28 washesNo lift

Up to 50% gray coverage
Semi-permanent hair color
(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 gray coverage


As the name suggests, this type of hair color permanently colors 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 color and/or adding your desired color with the dye. While the coloring remains on your hair, your uncolored hair at the roots will show through as your hair grows.

Here are some other facts about permanent hair color:

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


Semi-permanent hair color gently adds color molecules to the cuticle layer of your hair. Lasting for 6 - 8 washes, each wash lifts the cuticle—allowing color 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 hair color:

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

Here are some other facts about demi-permanent hair color:

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


Temporary hair color 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 color
  • Lower peroxide concentration than permanent color
  • 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 hair color (natural or previously colored) makes a difference in how semi-permanent hair color or permanent hair color turns out. If you’re not sure what shade to choose, go with this longstanding hair color rule: You can change your hair color successfully up to two shades lighter or darker than your starting color. 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 color, while fine hair, which is small in diameter, takes less time to absorb color. Dry or permed hair may absorb color more quickly. Since there are several factors that affect timing, it’s best to use a strand test to estimate coloring time.

Now that you know how hair color works, it’s time to color!