Hair colorants
How do hair colorants work?
any of us love to
change and enhance
the way we look by
changing our hair style and, in
particular, by altering the colour
of our hair. But how much do
we know about the process
of colouring hair and the way
it works?
M
Julie McManus
Why does our hair have
its natural colour?
Scientific Adviser at
L’Oreal, explains the
science behind hair
colorants...
Hair is given its natural colour
by colour pigments produced in
the hair root called ‘melanin
pigments’. There are two types
of melanin pigments that
determine hair colour:
‘eumelanins’ which create the
darker shades (ranging from
reddish-brown to black) and
‘phaemelanins’ which create the
lighter shades (pale yellow to
red). The hair’s natural colour is
determined by the proportions
of these different pigments.
‘Grey’ hair is an optical illusion
created by a mixture of white
(non-pigmented) and pigmented
hairs. As hair grows from the
root it can have a white base
on coloured hair.
White hair is created when
melanin pigments are no longer
present in the cells that make up
the hair – either melanin
production stops or the melanin
is unable to be transmitted into
the hair cells.
What are the types of
hair colorant?
There are three basic categories
of hair colorants, depending on
the duration of effect produced:
temporary, semi-permanent and
permanent.
Temporary hair colorants
modify the colour of the hair
temporarily and are readily
removed by washing. These
products tend to be ready-touse (no pre-mixing) and contain
‘direct’ colorants – these
coloured molecules are unable
to penetrate the hair fibre and
settle on the hair surface. The
combination of these molecules
with the natural hair colour
provides the new shade.
Semi-permanent hair colorants
are made of coloured molecules
that are able to penetrate the
hair. These colorants settle on
and within the scales of the
cuticle, becoming established
around the cortex without
modifying the hair’s natural
melanin. However, since these
molecules are also not bound to
the hair protein, the colour
gradually fades with washing.
The colour normally stays in for
up to 6-8 washes.
Oxidation hair colorants are
easy to recognise. Normally the
pack contains at least two
components which have to be
mixed together immediately
prior to use. Oxidative hair
colorants change the natural hair
pigments and give the hair –
depending on the formulation –
either ‘tone-on-tone’ colour
(also referred to as ‘demipermanents’) or ‘permanent’,
lasting colour.
Hair colorants
Permanent colorants cannot be
washed out and this is the more
traditional way of permanently
changing hair colour around the
world. They produce an effect
that is resistant to washing and
are chosen to provide long term
colour changes, ranging from a
subtle to dramatic, as well as
excellent coverage of ‘grey’ hair.
The two components that are
mixed consist usually of a tube
that will contain the colour
precursors and an alkaline agent
(the ‘colorant’) and a bottle that
contains hydrogen peroxide (the
‘developer’).
How do permanent
oxidation hair colorants
work?
The effect of each oxidative dye
is based on the following
components: an alkalising agent
– usually ammonia – and
oxidation colouring agents.
The alkaline agent has the effect
of opening the outer hair layer
so that colouring and oxidising
agents can penetrate into the
hair shaft more easily.
The starting materials for
developing the new colour are
called colour precursors which
are very small, colourless
molecules that only develop
their own colour nuance once
inside the hair.
The oxidising agent – usually
hydrogen peroxide – is mixed
with the colour precursors prior
to application. The oxygen is
released by the reaction
between the alkaline agent and
the oxidising product. It triggers
the actual colour-changing
reaction. Large, coloured
molecules are formed within the
hair’s cortex which are resistant
to being washed out of the hair.
Simultaneously, the oxygen
released will lighten the natural
melanin pigment in the hair so
that the new colour can be
seen, effectively replacing the
hair’s natural colour.
“Tone-on-tone” colorants also
include an oxidation step (for
example, mixing with peroxide)
but do not provide a marked
lightening of the hair’s natural
melanin pigment. Tone-on-tones
traditionally enhance or deepen
the natural hair colour. The final
colour is quite durable and will
gradually wash out after
approximately 28 shampoos.
New innovations
Hair colouring is one of the
oldest cosmetic treatments and
one of the most difficult. The
dye chemistry and formulation is
very challenging.
Recent innovations have
occurred in three places. Firstly
in the form of the product. In
order to get good mixing of the
dyes with the developer, the
developer and tint need to be
thin. However, thin products
simply run off the hair. To
overcome this, gel networks
form within the product on
mixing to turn thinner products
into a thick and easy to apply
final form.
The second area is in chelants.
These are normally added to
stabilise hydrogen peroxide.
However, hair also contains
metals such as copper that
penetrate from tap water. In
turn, these react with hydrogen
peroxide to form free radicals
that can damage the hair. By
choosing special chelants that
inactivate copper it is possible to
achieve increased hair protection.
The third is in ‘conditioning’.
In terms of the colorant product
itself, innovative conditioning
polymers have been
incorporated into some hair
colorant creams, which are able
to penetrate in to the cortex of
the hair and help reinforce hair
weakened by the colouring
process. Furthermore, new
formulations for ‘in box’
conditioners are able to give
longer term durable conditioning
to coloured hair. When hair is
coloured with permanent
colours a unique fatty acid is
removed from the hair surface.
This changes the surface from
being hydrophobic to
hydrophilic and in turn this
changes the interaction of
uncharged conditioning
molecules with the hair surface.
As a result new conditioning
molecules have been designed
that match the surface energy
of the hair fibre to help them
deposit and spread on the
surface.
The CTPA is the trade association for the UK cosmetic, toiletry and perfumery industry.
For further information on cosmetic products and their regulation, visit www.ctpa.org.uk