The Science of Your Hair


To understand the science of hair colour, first it is important to understand WHAT we are colouring. Let’s start with a review of hair structure.


Hair fibres consist of three parts: The cuticle, the cortex and the medulla.

The Cuticle is approximately 10 layers of flat, overlapping, scale-like structures that are responsible for the condition of your hair as it helps protect the inner portion of your hair structure—the cortex.

The Cortex is the group of spindle-shaped cells aligned along the fibre which account for about 70-90% of the hair bulk. The cortex contains hair’s natural pigment called melanin and is also where the colouring process takes place. The size, shape, distribution of the melanins determine the overall colour of hair.

The Medulla is the centre of the hair fibre. This is the core of elongated cells running down the middle of the hair fibre.


Since the natural colour pigment (melanin) is in the cortex, deep inside the hair, and the cuticle is designed to protect the cortex, dyes or bleaches must penetrate the cuticle, travel through the cortex and remain active long enough to colour hair.

There are also a variety of hair types—straight, wavy, curly or anything in between. Minor differences in our genes can make large differences in hair, so it is important to understand your hair type before colouring. For example, since Asian hair is thicker and coarser than Caucasian hair, it can be more difficult for hair colour to penetrate and lock in. Therefore, a longer colouring time may be necessary.


  • Hair is found on about 95% of the total skin area
  • The average head contains over 100,000 hair follicles
  • On a baby’s head there are 1,100 follicles per square cm; by age 25 this falls to 600, and by age 50, you’re down to about 250
  • Hair is very strong, in fact, a strand of hair is stronger than a copper wire of the same thickness
  • Hair grows at a rate of 1 cm per month
  • Each hair on the scalp will grow for about 1000 days and then fall out
  • Each follicle grows about 20 new hairs in a lifetime, which grow for several years until they fall out
  • We naturally lose 50 - 100 scalp hairs every day
  • No new follicles form after birth