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International Journal of Research in Dermatology | September-October 2021 | Vol 7 | Issue 5 Page 748
International Journal of Research in Dermatology
George NM et al. Int J Res Dermatol. 2021 Sep;7(5):748-752
http://www.ijord.com
Review Article
What do we need to know about hair straightening?
Neethu Mary George1*, Amruthavalli Potlapati2
INTRODUCTION
Hair straightening is a very popular hair procedure around
the world. A straight hair is considered as a sign of beauty
by many. Hair straightening methods have also evolved
over time. With urbanization, people are opting for various
methods to increase manageability of hair, the most
common being hair straightening. Though it’s a very
common procedure, it is associated with various adverse
events. With new straightening methods coming in, the
side effects are also coming down. A study done in Saudi
Arabia revealed that 33.5% repeated their chemical
procedure, for easy hair management being the commonest
reason followed by nourishment and repair of hair.1 We
performed a literature search in the scientific database
PubMed using the terms “straightening”, “hair”, “ironing”,
”Brazilian keratin” and “cysteine”. We also consulted hair
stylists from professional hair salons and also from beauty
colleges prior to preparation of the article. The current
article focuses on various hair straightening methods and
the chemistry behind it. It makes a dermatologist aware
about the basic mechanisms involved, possible effects and
thereby improve hair health.
TYPES OF HAIR STRAIGHTENING
Permanent
Hair rebonding or Japanese/thermal reconditioning.
Semi-permanent
Keratin/Brazilian blowout/Brazilian Keratin treatment
This technique was introduced in 2003 in Brazil. It
reduces the static electricity and makes hair more
manageable.
DOI: https://dx.doi.org/10.18203/issn.2455-4529.IntJResDermatol20213356
ABSTRACT
Hair straightening is a popular hair procedure. The first hair straightening products were used for African hair. Various
modes of hair straightening methods are currently being used. Temporary methods like blow drying and ironing are
used for easy manageability of hair, both by modern men and women. Salon- based hair straighteners were initially
permanent relaxers which, with time, evolved to formaldehyde-free hair strengthening procedures like hair Botox which
is currently in trend. It improves hair manageability, increases hair strength and reduces frizz without producing much
chemical damage to hair and by maintaining their natural waves, thereby producing a more natural look. We performed
a thorough literature search on the topic in PubMed, consulted various hair stylists and beauty school professors prior
to formulation of this article. The article aims at understanding the basic mechanisms involved in various hair
straightening methods which helps us to advice patients on a wholesome care of hair.
Keywords: Hair straightening, Keratin, Cysteine, Formaldehyde, Brazilian keratin
1Department of Dermatology, Marsleeva Medicity, Pala. Kerala, India
2Department of Dermatology, Sri Siddhartha Medical college, Tumkur. Karnataka, India
Received: 09 July 2021
Accepted: 13 August 2021
*Correspondence:
Dr. Neethu Mary George,
E-mail: neets.1x@gmail.com
Copyright: © the author(s), publisher and licensee Medip Academy. This is an open-access article distributed under
the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial
use, distribution, and reproduction in any medium, provided the original work is properly cited.
George NM et al. Int J Res Dermatol. 2021 Sep;7(5):748-752
International Journal of Research in Dermatology | September-October 2021 | Vol 7 | Issue 5 Page 749
Cysteine treatment
They utilise carbocysteine-based products for the purpose
of hair straightening.
Hair Botox
It is a deep conditioning treatment that helps to restore hair
damage. They contain a cocktail of nourishing ingredients
such as vitamins, amino acids, glyoxylic acid, collagen
complex, ceramides and many more, which forms a
protective coat on hair.
Temporary/non chemical
They last only until the next wash. Hair has to be pre‐
wetted, to break the hydrogen bonds of keratin, thus
permitting temporary opening of its original structure.
Rapid drying with the hair dryer maintains the flat shape
of the strand. The application of a hot iron mechanically
fixes the shape of already straight wet hair. This is usually
done by men and women as a home-based procedure using
blow dryer straightening iron etc.
CONSTITUENTS OF VARIOUS HAIR
STRAIGHTENING PRODUCTS
Straightening products are widely used to change hair
shape. Chemical based hair relaxers are broadly classified
as “Lye” relaxers, no‑lye relaxers and “thio” relaxers.2
Lye relaxer
They contain sodium hydroxide as an active ingredient and
are also known as soda- containing straighteners. They act
by the lanthionization reaction, in which the hydroxyl ion
breaks the disulfide bonds generating lanthionine. Here,
disulphide bonds undergo rearrangement and cysteine is
ultimately converted to lanthionine. This causes
irreversible hair straightening.3 They are extremely
alkaline with a pH of 13–14 with a higher scalp irritation
potential. The transformation of cystine into lanthionine
and a high pH causes weakening of the hair fibre, through
a decrease in mechanical strength and higher protein
loss.4,5
No-lye relaxers
They contain lithium, guanidine hydroxide, or ammonium
thioglycolate. They are known as non-hydroxide
straightening products. They are less irritating compared
to sodium hydroxide.
Straightening with reductive agents (thio-relaxers)
Ammonium thioglycolate (AT), ethanolamine
thioglycolate, cysteamine hydrochloride, glycerylmono-
thioglycolate, ammonium sulphite, ammonium bisulphite.
AT is the most common and has a pH of 9-9.3.
Thioglycolic acid and its salts
They include ammonium thioglycolate (AT), aminomethyl
propanol thioglycolate, and ethanolamine thioglycolate.
Like hydroxides, thiols also swell the hair shaft, but with
no lanthionization reaction. It selectively weakens the
hair's cystine bonds and reduces the disulphide bonds
instead of disrupting the entire protein. In the procedure
with ammonium thioglycolate, the disulphide bonds are
converted to sulphhydryl groups to allow the mechanical
relaxation of the protein structure of hair fibres following
which the thioglycolate is oxidized (neutralized) with
ammonia, monothanolanine, sodium hydroxide or other
oxidising agents. If a hot iron is applied during the process,
the permanent straightening can be achieved. This is the
basis of the process called “japanese hair straightening or
thermal reconditioning.” The use of thioglycolate causes
less protein loss than hydroxides whereas oxidising agents
like hydrogen peroxide may cause the hair colour to fade.
Hair conditioning substances may be added to
thyoglicolate straighteners in order to minimize hair
damage.
Straightening utilising formaldehyde
This is used in methods like Brazilian Keratin Treatment.
Formaldehyde and other aldehydes are not straightening
products but act as a cross linking agent. Water initially
breaks hydrogen bonds of the keratin molecule, with hair
wetting. The formaldehyde then forms crosslinks with the
keratin filaments which fixes the hair as straight. The light
that strikes the hair reflects from the realigned keratin
filaments and create good shine from hair post procedure.
The aldehydes are compatible to every other hair
treatment, such as bleaching, permanent dyes and lye/no-
lye relaxing.
Glyoxylic acid and its variants
Glyoxylic acid (GA), also called formic acid or oxoacetic
acid, is an organic compound. They are being promoted as
“formaldehyde –free” but act as formaldehyde releasers
when subjected to high temperatures.6 GA straightening
have semi-permanent results, which lasts for only up to
five to ten washes. GA penetrates through cuticles and acts
on the hydrogen bonds and the amino acid tyrosine of the
cortex. It causes no break in the disulphide bridges, but a
change in the shape of these bonds and forms a
polymerized structure in the hair shaft, leading to
straightening of hair. The temperature is highly associated
with this process, because higher the temperature, the more
the formation of these products. Examples of glyoxylic
acid derivatives are glyoxyloyl carbocysteine, glyoxyloyl
keratin aminoacid oxoacetamide.7 Despite the film-
forming effect, giving it a shiny appearance, this substance
disturbs the integrity of the keratin and the tensile strength
of the shafts, thereby making it more fragile.
George NM et al. Int J Res Dermatol. 2021 Sep;7(5):748-752
International Journal of Research in Dermatology | September-October 2021 | Vol 7 | Issue 5 Page 750
Straightening using carbocysteine- based compounds
They include glyoxyloyl carbocysteine or oxoacetamide
carbocysteine. It has no effect on hair keratin.
Carbocysteine hair treatment represents the combination
of glyoxylic acid + cysteine + acetic acid.8 Glyoxylol
carbocysteine, the most commonly used ingredient in
Cysteine treatments, has a pH nearer to our hair and scalp
and is thus less damaging and they also release a little
formaldehyde in the ironing step. Though the straightened
hair in Cysteine treatment is not as poker straight as
compared to conventional relaxer-based straightening or a
Brazilian keratin treatment, it gives more shine to the hair
compared to the other two.
Keratin based particles
The synthetic hydrolysed liquid keratin penetrates quickly
to the cortex and reacts with the keratin of human hair.
Formaldehyde released during heating helps in fixation of
hydrolysed keratin in the natural keratin of the hair.6 This
produces a water-proofed film around the hair and seal the
cuticles, improving the shine and smoothness of virgin and
bleached hair. This film is not so protective since the shaft
remains fragile and susceptible to fractures after minimal
trauma.9,10
Other contents in straightening formulation
Silicone: Silicone forms a uniform, continuous, and
hydrophobic coat improving resistance and reducing
surface tension of the styled hair. They substitute the
natural sebum, without providing an oily feeling, and
reduce the damages caused by oxidizing and straightening
treatments. Example- polydimethylsiloxanes,
dimethicone.
Proteins like hydrolysed proteins, amino acids.
Conditioning agents: Shea butter, cocoa seed butter etc.
Additives like fragrance.
PROCEDURE
The hair is examined prior to selecting the ideal relaxer for
a consumer, the strength and type of relaxer determined
based on the coarseness, degree of curliness, porosity and
previous treatments done. The hair then is shampooed to
remove sebum or products that might interfere with the
action of the straightening solution. The hairline and ears
are protected with petrolatum or cotton to avoid the highly
alkaline solution to cause burns on skin. The hair is
separated into sections. Chemical relaxers are applied on
clean hair. Once the cream is applied, it is smoothed
section-by-section until the hair is straightened. The
amount of time the relaxer is left on the hair is determined
by the hair porosity, thickness and the manufacturer’s
instructions, following which the hair is rinsed. The relaxer
should be completely rinsed out before the hair is
shampooed. Finally, a neutralizing shampoo is used to
bring the pH back to normal and to close the cuticle.
For hair Botox, the hair is washed, skipping conditioner,
with a clarifying shampoo to remove any residue on your
hair and open your hair cuticles. Afterwards, the mixture
will be applied and left on for roughly 45 minutes, before
being washed off with a gentle, low or sulphate-free
shampoo, blow-dried and typically, sealed with
straighteners.
To prevent irritation, hairdressers are advised to wear
gloves while the procedure is being done.
ADVERSE EFFECTS
Despite being a very common procedure, hair
straightening is associated with multiple side effects. The
no-lye relaxers are less irritating to the scalp than lye
relaxer (sodium hydroxide). The most common adverse
effects reported after chemical hair straightening were
frizzy hair, dandruff, hair loss, thinning and weakening of
hair, greying of hair and split ends.11 The side effects are
not seen just for clients but all also for hairstylists.
Evidence of cancer among hairdressers have been
described by many.12 It was first reviewed by the
International Agency for Research on Cancer (IARC)
which reported an increased risk of urinary bladder cancer,
lung cancer, upper aero-digestive tract cancer, breast
cancer, and non-Hodgkin’s lymphoma in these
professionals.13 Hairdressers have also demonstrated an
increased frequency of DNA damage.14
Allergies
Irritant and allergic contact dermatitis are common. It can
be caused by formaldehyde, fragrance, parabens,
quaternium-15 (a formaldehyde donor),
methylisothiazolinone etc.
Hair damage
Weathered and chemically treated hairs can get worn off
of 18-MEA in cuticle which leads to hair fibre fracture and
makes the hair hydrophilic. Chemical treatments make hair
more porous and this usually occurs if the hair is exposed
to straightening chemicals for long time or high
concentration.15 The pH of the straightening formulation
also affects the hair strength wherein a low pH can cause a
better straightening but lesser hair strength and vice versa.7
Heat can cause denaturation of various hair proteins and
cause hair damage. However, it was found that using a hair
dryer at a distance of 15 cm with continuous motion causes
less damage than drying hair naturally.16
Alopecia
Scalp inflammation and scarring alopecia have been
reported with both lye and no-lye relaxers.17 Telogen
effluvium may occur, usually because of excessive or
improper use of straightening agents.18 High-tension
hairstyles are best avoided on relaxed hair to prevent
traction alopecia.
George NM et al. Int J Res Dermatol. 2021 Sep;7(5):748-752
International Journal of Research in Dermatology | September-October 2021 | Vol 7 | Issue 5 Page 751
Repetition of procedure
Most of the hair straightening needs to be repeated
regularly as the newly grown hair will be having a
completely new texture and appearance compared to the
old. Careful application over the new growth is needed as
overlap over the straightened hair causes excessive
breakage. Semi-permanent procedures like hair Botox
lasts for only few washes.
Short term side effects
They include scalp itching during the procedure and
burning sensation in eyes, nose, and throat have been
reported.19
Carcinogenicity
Various agents like formaldehyde, being a known
carcinogen has made various regulations on the use of
formaldehyde in hair products.20
Others
Formaldehyde causing urticarial have been reported.21
COLOURING WITH STRAIGHTENING
Colouring either with hydroxides or with thioglycolate,
may cause hair damage and breakage in chemically
straightened hair as both are highly alkaline. Therefore, the
demi-permanent hair dyes are preferred over the
permanent ones when both colouring and straightening are
combined. Ammonium thioglycolate or guanidine
hydroxide caused a small increase in protein loss,
suggesting that these straightening products could be
better than hydroxides for individuals wishing to combine
both treatments.22
But with current methods like hair Botox, we can combine
both without causing much hair damage. It is not
recommended to dye your hair right after a hair Botox
treatment and a gap of at least two weeks should be given
before hair colouring. The chemicals present in permanent
dyes can wash off the coat formed after hair Botox. Hence
it is better to do Botox post colouring if the client wishes
to combine both. But a Botox can affect the tone of already
coloured hair.
HAIR STRAIGHTENING IN PREGNANCY
Chemical hair straightening is usually not recommended
in pregnancy. It has been found that children exposed to
hair straightening compounds prenatally especially
formaldehyde, perchloroethylene, acetaldehyde increases
risk of developing Wilm’s tumour and early age of onset
of leukemia.23,24
CONCLUSION
Equipped with this knowledge, we as dermatologists will
be better able to counsel our patients on the appropriate use
of relaxers, helps to choose the ideal straightening method
depending on the need and hair condition, time the
procedure and educate them on care of processed hair.
Funding: No funding sources
Conflict of interest: None declared
Ethical approval: Not required
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Cite this article as: George NM, Potlapati A. What
do we need to know about hair straightening? Int J
Res Dermatol 2021;7:748-52.
