This is a very good question and everybody who
is ever thinking of coloring their hair should
know more about how it works. Of course nowadays
the products are not really toxic anymore nor are
they really smelly like they used to be.
The main ingredients involved in any coloring
process are hydrogen peroxide and ammonia.
The other ingredients are dye precursors (and
moisturizers to help protect the hair from
The ammonia solution makes the hair cuticle
(the outer layer) swell. This allows the other
chemicals to penetrate into the cortex (core)
where the natural melanin pigments are stored.
Hydrogen peroxide (the developer or oxidizing
agent) helps initiate the coloring process.
Depending on its strength it bleaches the hair
pigment and it oxidatively couples the dye
precursors (aromatic amines) into larger dye
molecules that can not escape the cortex. This
makes the hair color permanent.
So when you go from blond to a darker color -
say brown- permanent hair colors use the
interaction between the ammonia and the peroxide
to create a new color base in your hair shafts. If
you go the opposite direction - from brown to
blonde- first bleach is used to strip the color
from the hair. Then the ammonia-peroxide solution
creates the new color and deposits it in the hair
shaft. If you use a semi-permanent color the hair
is only coated with color rather than deposited
into the hair shaft.
Some of the hair dying products for men have
lead (II) acetate in it. It is used to darken hair
by reacting with the sulfur present in the hair
color product and in the amino acids cysteine and
methionine. The product of the reaction is black
lead (II) sulfide.
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