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Whether or not a perm will 'take' well depends on the
basic nature of the hair, its past history of chemical treatments,
if any, and the skill of the technician or stylist. Hair that
has had a long history of perming, perhaps combined with tinting
or bleaching, may have become so damaged as to be near the
limit of what it will tolerate.
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HAIR
FACTS
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pH
and hair
The
key to the perming process lies in the fact that perming
solution is alkaline. What exactly does this
mean in relation to hair?
When scientists talk to each
other about alkaline solutions and acid solutions, they
need a way of measuring alkalinity and acidity. The
scale they use for their measurements is called the
pH scale.
The pH scale ranges from pH
1 to pH 14. All you need to remember is that acids
have pH numbers less than 7. Alkalis have pH
numbers greater than 7. The more acid the solution,
the lower is the pH number; the more alkaline the solution,
the greater the pH number.
pH is measured using special
indicator papers which change color when the
pH changes.
Hair responds to changes in
pH. If a hair is placed in an alkaline solution it swells,
and the scales of the cuticle lift. In a slightly acid
solution, the scales lie smoothly and the hair is soft.
In a strongly acid or alkaline solution, however, the
keratin protein starts to break down.
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The
perming process
The hair is first washed and then wound on to some kind of
former, such as a curler or a rod. The perm lotion is applied
to the hair. Because the lotion is alkaline (pH about 9) the
scales of the cuticle open slightly, allowing the lotion to
flow under the cuticle and into the cortex. Here it reacts
with the keratin of the cortex, breaking some of the disulphide
cross-links within and between the protein chains. The hair
swells and 'softens', so that it can stretch to take up the
shape of the formers.
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After a while the perm lotion is thoroughly rinsed
away and a neutralising lotion is applied. This re-forms
the broken cross-links, which makes the hair harden into its
new, curlier shape. This stage is the key to a successful
perm: failure to rinse and neutralise properly can lead to
many problems, including scalp irritation and damage to the
structure of the hair shaft.
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HAIR
FACTS
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What
happens during perming
Today's
'cold' permanent wave lotions contain substances called
reducing agents, in an alkaline solution. The
reducing agent most often used is called ammonium
thioglycollate. Reducing agents act on the keratin
in the hair, breaking the disulphide linkages that join
the pairs of cysteine units together. The result is
that the keratin softens and swells. The softened hair
is then put into its new shape. As it is manipulated
the cysteine linkages slip past each other and realign
themselves with new cysteine partners see (page
91).
Neutralising lotion is then
applied. This contains oxidising agents. One
that is often used is hydrogen peroxide, the
same substance that is used in hair bleaches. Oxidising
agents work in the opposite way to reducing agents.
They make the cysteine units link together into pairs
again, hardening the hair and giving it its new, permanent
shape.
In hair that has been repeatedly
permed the original disulphide cross-links may have
been broken and re-formed so many times that hardly
any remain.
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In order to illustrate the process
of permanent waving, we will follow a client through the full
procedure.
This client, like many others, wants
her hair put into a manageable style, with curl and body.
It is vital that the stylist understands the past history
of her hair. It is permed every three or four months, and
tinted more frequently. Fortunately her hair is naturally
very resilient, and has not suffered unduly. In expert hands,
a perm should be straightforward.
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