Chapter 5: Hair Relaxers Defined and Refined - Allured Books

Hair Relaxers Science, Design, and Application
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Chapter 5
Hair Relaxers Defined
and Refined
Hair relaxers are thick heavy creams consisting of very high pH
(12–14) oil-in-water (o/w) emulsions that provide straightening effects
through a chemical reaction combined with mechanical manipulation
of the hair. Due to the extreme alkalinity of the relaxer, the emulsion
must be of high viscosity so that the cream does not drip and cause
irritation to the scalp during application or when it is combed through
the hair.
Defining Characteristics of Relaxers
Hair relaxers are characterized by their extremely high pH, resulting
from the presence of a strong alkali. Relaxer treatment results in a
straightening effect by a reactive process in which hydroxide ions cleave
disulfide (S-S) bonds, combined with mechanical manipulation in
which the hair is stretched, either by hand or with a comb. This process
is always in a very high pH environment of about 12.5–13.5. Relaxer
treatment should be administered carefully, since it can be harmful to
the scalp and hair if the relaxer is not properly applied or if processing is
not correctly controlled.
Hair relaxer creams consist of three principal components, or
phases—an alkali phase, an oil phase, and a water phase. The alkali
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Chapter 5
phase constitutes the active component of the relaxer and consists of a
water-soluble/water-dispersible alkaline agent that is prepared separately
and is added to the emulsion once it is formed.
The water phase usually consists of a mixture of water and propylene
glycol, the latter of which is a humectant added to prevent excessive
water loss. The water phase is added to the oil phase with heating to
form the emulsion; in the case of a relaxer, an o/w emulsion forms
as the batching process proceeds, provided it is formulated properly.
Relaxer preparations are just one example of the many o/w emulsions
that are used in personal care products. It is important for first-time
formulators to note that the type of emulsion (o/w or w/o) formed is
dependent on the particular hydrophilic-lipophilic balance (HLB) of
the emulsifier mix in the oil phase, not on the physical methods or
sequence of combining the two phases.
The addition of the active phase to the emulsion is a critical step
and must be done with care, because the alkalis are very reactive,
especially in the case of sodium hydroxide. Once the active phase has
been prepared separately, it should be brought to the same temperature
as the emulsion before it is added. When formulating a lye relaxer, it
is advisable to take further precautions and lower the heat of reaction
of sodium hydroxide before adding it to the emulsion. Otherwise, the
highly reactive sodium hydroxide in water could react aggressively to
break the emulsion, resulting in a longer batching process that slows
down re-formation of the batch. In such a situation, very cold water is
rapidly circulated around the manufacturing tank to bring down the
temperature, so as to normalize re-formation of the emulsion.
As discussed earlier, the active in hydroxide relaxers may be a strong
base, such as sodium hydroxide (lye relaxer), or lithium hydroxide and
potassium hydroxide (no-lye, no-mix relaxers); in no-lye relaxers, the
alkali used is the weaker calcium hydroxide/guanidine carbonate base
and is formulated in two separate steps to yield guanidine hydroxide.
It should also be noted that the methods of manufacturing a sodium
hydroxide relaxer and a no-lye relaxer are somewhat different, in that
the types of equipment used to ensure uniform distribution of the
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Hair Relaxers Defined and Refined
various actives are not the same. Although no-lye relaxers claim to
have no traces of lye-like or caustic soda character, this statement is
not entirely true, because the three hydroxides are in the same family
of metal hydroxides as sodium hydroxide. Furthermore, various
opinions over the use of lye vs. no-lye actives have been bandied about
for years but are largely the result of “market-speak” and not scientific
verification.
The oil phase typically contains all the primary oils, plus high
HLB surfactants (emulsifiers). Petrolatum and mineral oil are used
almost universally, often as a mixture with other oils and fats. The
choice of surfactants is extremely important, as it is absolutely
necessary to have the right emulsifier mix in the right ratio to achieve
simultaneous release of the oils and active during hair processing. The
types of surfactants used are typically nonionics, but in some cases,
anionic surfactants are used. Nonionic surfactants are the emulsifiers
of choice because they have no charges, offer a wide range of HLBs
with a high degree of electrolyte tolerance, and offer some degree of
conditioning that is conferred to the hair and scalp during relaxer
application. Thus, the oil phase not only serves as the emulsifier for
simultaneous release of the oil and active, but also acts as a conditioning
component to provide the scalp with some barrier protection, add sheen
to the hair, and improve its combing properties.
Refining the Relaxer
Once hair relaxers were commercialized, their popularity gained
ground quickly with African-Americans and other women with very
curly hair. However, over time, reports that hair loss and breakage were
occurring with prolonged use of these products had begun to trickle in,
alerting ethnic hair care companies of the problem.
Unfortunately, in those days little data had been gathered on the
long-term effects of straightening the hair or on the emulsion aspects
of delivering strong alkali actives. Attempts to improve these earlier
systems had product development chemists back at the bench scrambling
to find solutions and experimenting with such variables as the
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Chapter 5
percentage of water in the formulation vs. irritation level, the ability
of the relaxer to penetrate hair vs. irritation level, and the active level
of sodium hydroxide vs. a tolerable irritation level. 1
The original hair relaxer had been developed as a caustic soapbased
system using stearic acid and sodium hydroxide, but by the
1950s lye relaxers were being prepared as w/o emulsions in which
the sodium hydroxide was first dissolved in water and then this solution
was dispersed or emulsified into an oil mixture. After making a
series of adjustments to the concentration of lye and oils, formulators
determined that the optimum ratio was a 50/50 mixture of the oil and
water phases. Formulated at this level, the relaxer lessened the incidence
and severity of burning and stinging associated with the original
version, but still effectively straightened the hair. Any emulsion with a
higher concentration of oils reduced the straightening properties and
any with a higher concentration of water and active caused considerably
more irritation.
Despite their improvement over the earlier soap-based product,
these lye relaxer emulsions still had high irritation potential and
often contained levels of sodium hydroxide as high as 3.5%. This
required a pre-coating or “base layer” of petroleum jelly applied to the
scalp and hairline to protect the skin around the forehead, ears, and
neckline. Thus, the term base relaxer was adopted. Due to its tendency
to irritate the scalp and surrounding skin, and the extra time needed to
pre-treat the area, the base relaxer fell into disuse and was eventually
replaced by the no-base lye relaxer, which was generally available only
to professional stylists and subsequently became the relaxer of choice
for salon use.
As more knowledge about emulsion control was gained, formulators
began to realize that the formation of micelles and the configuration
of water/oil droplets in an emulsion affected delivery of the active.
When the relaxer emulsion was applied and massaged into the hair, the
micelles broke, releasing the water/lye mixture and allowing the active
to penetrate the cortex, yet leaving the oil portion on the cuticle where
it could provide conditioning effects. This simultaneous action of the
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Hair Relaxers Defined and Refined
water with the actives and oils on the hair and scalp constitutes the core
of good relaxer technology.
As a result of this improvement, a base layer of petroleum jelly was
no longer necessary, marking the advent of no-base relaxers. Unlike
base relaxers, no-base relaxers contain only 1.5–2.5% actives, and at
this lower concentration, the hairline alone needs pre-treating, not the
scalp. These improvements in the relaxer also gave the product more
stability, caused less damage to hair, and therefore, made it much more
marketable.
Irritation to the scalp, however, remained a problem. The development
of the no-lye relaxer (calcium hydroxide/guanidine carbonate)
evolved out of efforts to reduce the scalp issues that continued to
persist with the use of hydroxide relaxers. These no-lye relaxers were
introduced in 1978 and were geared to consumers. Sold as kits, no-lye
relaxers consist of a base cream containing 4–7% calcium hydroxide,
plus a separate liquid activator containing guanidine carbonate. The
two parts are combined in situ just before use, at which time they react
to form calcium carbonate and guanidine hydroxide, the latter of which
is the active that straightens the hair. No-lye relaxers do not need basing
and usually include built-in conditioners in the kit intended to help
repair hair damage “on the spot” as it occurs during relaxing. Although
no-lye relaxers were found to be less irritating to the scalp, they were
reported to be less effective than hydroxide relaxers in relaxing tight
curls. 1,2 However, this observation is more likely to be the result of
inadequate mixing or improper reacting between the base cream and
the activator.
Today, there is no absolute baseline established for the amount of
actives that should be used in relaxer formulas; however, it is essential
for the formulating chemist to have a good grasp of the chemical
nature of each of the actives and their reactivity before determining
what levels to use. Lye relaxers manufactured in the United States and
around the world generally have active levels ranging from 1.9–2.5%
by weight of sodium hydroxide, depending on their strength. In
no-lye relaxers; the levels for calcium hydroxide usually range from
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