Types
of chemicals used in permanent waving and straightening products
There are many products available for waving and straightening
hair but they are all based on one of three basic chemical categories:
1) alkaline hydroxide creams, 2) thioglycolate lotions or creams
(also known as Jherri curls), and 3) ammonium or sodium bisulfite
lotions. The alkaline hydroxide category can be further subdivided
into "lye" products which contain sodium hydroxide and
"no-lye" products that contain calcium hydroxide. The vast majority
of hair waving products are thioglycolate based, while the hair
straightening products are more mixed and may be based on any of
the three chemical types. All of these chemicals react with, and
alter, the chemical structure of the hair. They break the disulfide
bonds in hair keratins to make the hair pliable and allow restyling,
then the biochemical bonds are allowed to redevelop and fix the
hair in its new style. The result should be permanent and will not
change on exposure to water or after shampooing as occurs with hot
combs, rollers, and irons or with cosmetic oils and resins.
Hydroxide
hair straighteners
These products contain quite caustic alkaline chemicals. They act
by swelling the hair, physically and chemically breaking (hydrolyzing)
the disulfide bonds in keratins. The action is very rapid and allows
the process of hair straightening to be conducted quickly. The chemical
reaction is stopped and the hair fixed in its new shape by extensive
rinsing with water.
Because the chemicals involved are quite potent and act in a very
short time, the chemicals should not be left on the hair for very
long, usually no more than 10 minutes. If the chemicals are left
on the hair for too long the hair may become severely and irreversibly
damaged. The chemicals are also quite damaging to the skin and may
cause chemical burns. To avoid this the scalp skin is usually covered
with a protective cream before applying the alkali agent. If the
protection is not complete there can be a response with dermatitis
and swelling of facial skin. If no protection is used at all the
result can be devastating, the product may cause significant chemical
burns. Because of these risks involved with alkali straighteners
the products are only found in the salon and are not generally available
for use at home.
Thioglycolate
products for hair waving and straightening
Both waving and straightening products may be based on a thioglycolate
solution. For hair straightening the thioglycolate products are
generally applied to freshly washed, damp hair for somewhere between
5 and 15 minutes and the hair is combed through gently for 10 to
20 minutes. The thioglycolate chemicals break the disulfide bonds
in the keratins and after straightening the hair the bonds are promoted
to reform and hold the hair in its new straight shape by washing
out the chemicals and applying an oxidative neutralizer, usually
hydrogen peroxide. While very good at waving hair, thioglycolate
based hair straighteners are usually not so good as hydroxide and
bisulfite based products. The thioglycolate chemicals are not quite
so potent and quite so successful in breaking the biochemical bonds
in the hair. Getting a really straight hair look is more difficult
with thioglycolates. However, their advantage is they carry less
risk of skin or hair damage compared to the hydroxide or bisulfite
based products.
Bisulfite
hair straighteners
Bisulfite straighteners are a newer method of chemical processing
first developed in the early 1970s and popular with both salon professionals
and for home use. They work in the same way as hydroxide and thioglycolate
based products by breaking the disulfide chemical bonds in keratins.
Typically the bisulfite lotion is applied to freshly washed, damp
hair and then the scalp is covered with a plastic cap or turban
to make sure it does not dry out. The lotion is left in place for
about 15 minutes. The hair is then combed for up to 20 minutes to
straighten the hair. The chemical is then washed out with lots of
water and a stabilizing solution is applied to trigger the reformation
of the disulfide bonds and fix the hair in a straight form. Often
a conditioner is applied as a final step. Bisulfite straighteners
are quite effective and better than thioglycolate based straighteners.
They are arguably somewhat safer to use than hydroxide based products.
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