How
bleaching and dyeing hair works
The urge to color hair has been with us for thousands of years.
At its simplest, tribes in africa would (and a few still do) coat
the hair in a red clay mixture. Egyptians discovered henna and used
this as an effective hair dye. Other natural plant dyes made from
black walnut sheall or bleaches made from natural acids like vinegar
were also popular. In the nineteenth century lead salt based compounds
were used to color the hair, primarily to color gray hair. However,
the first safe commercial hair dye from which all the current hair
dye formulations are derived was created in 1909 by French chemist
Eugene Schuller, using the chemical paraphenylenediamine. Hair coloring
is very popular today. Some surveys suggest up to 75% of women in
the USA color their hair and hair dye is also being used by a growing
percentage of men too.
Hair is mainly made from keratin. The natural color of your hair
depends on the ratio and quantities of two proteins contained in
the keratin called eumelanin and phaeomelanin. Eumelanin makes brown
to black hair shades while phaeomelanin is responsible for blond
and red colors. You can have one or both melanin pigment types and
the ratio and concentration of each determines your shade of hair
color. The absence of both melanin types produces white/gray hair.
To change hair color more than a few shades you need to bleach
the hair first to get rid of these natural pigments. First, the
hair cuticle has to be opened up to enable the bleach to penetrate
inside the fiber to get to the pigments. This is usually done by
mixing the bleach in an alkaline solution. The alkali opens up the
hair cuticle while the bleach goes inside. the hair.
The bleach, usually a hydrogen peroxide solution, reacts with the
melanin in hair, removing the color in an irreversible chemical
reaction. The bleach chemical is designed to oxidize the melanin
molecule. The melanin pigment remains present in the hair fiber,
but the oxidized molecule is colorless. Complete bleaching tends
to leave hair a yellow color rather than pure white. The yellow
color is the natural color of the keratin structural protein that
makes up the hair fiber. The degree of color left after bleaching
also depends on your production of eumelanin and phaeomelanin pigments.
Bleach reacts more readily with the dark eumelanin pigment than
with the phaeomelanin, so some gold or red residual color may remain
after lightening depending on how much phaeomelanin your hair follicles
make.
This process may be enough for those who just want their hair lightened,
but more usually a finishing dye is added, often to neutralize any
remaining red residual color and to hide the yellow color of the
keratin which does not look a very natural yellow. Again, the cuticle
has to be opened up for the dye to get inside the hair fiber so
the dye is usually applied in an alkaline solution, usually made
with ammonia, which opens the cuticle.
Once the cuticle is open, the dye reacts with the inner portion
of the hair, the cortex, to deposit the color. It's essentially
the same process as lightening, except a colorant is then bonded
in the hair fiber. The alkaline chemical that opens the cuticle
and allows the hair color to penetrate the cortex of the hair also
acts as the catalyst when the permanent hair color comes together
with the peroxide to fix the color in place. Peroxide is used as
the developer or oxidizing agent. The developer helps remove some
pre-existing color which may be enough to lighten hair a few shades
without prebleaching. As the melanin is decolorized, a new permanent
color is bonded into the hair cortex. However, when an individual
wants to go from dark hair to very light hair a prebleach is usually
required to get rid of most of the natural pigment first. So, both
bleaching and dyeing can occur simultaneously, but chemically the
technique is still a two step process, first remove the natural
hair pigment and then fix the hair dye in place. Peroxide involved
in both bleaching and dyeing processes breaks chemical bonds in
hair, releasing sulfur, which accounts for the characteristic odor
experienced in hair coloring. At the end of the process, conditioners
are used to close the cuticle after coloring to seal in and protect
the new color.
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