Hair colouring: what a dermatologist should know?

Abstract

p>Hair is an important part of body and a major factor in self-image. A wide variety of hair cosmetic preparations are available and are used regularly by most of the world’s population. Hair colouring is one of the commonly done procedure. However, any chemical treatment, normal grooming habits and environmental exposure can produce changes in hair texture or hair breakage. It is necessary for a dermatologist to know the basis of hair colouring, the procedure and the possible side effects it can cause. Also post colour care is also to be known about to prevent further damage to treated hair. This article explains the basic chemistry and mechanism involved in hair dyeing and the basic facts a dermatologist should know.</p

Full text

International Journal of Research in Dermatology | May-June 2021 | Vol 7 | Issue 3 Page 496
International Journal of Research in Dermatology
George NM et al. Int J Res Dermatol. 2021 May;7(3):496-502
http://www.ijord.com
Review Article
Hair colouring: what a dermatologist should know?
Neethu Mary George*, Amruthavalli Potlapati
INTRODUCTION
Hair is present in various colours and textures varying
with race and ethnicity. Hair colour is determined by the
melanocytes found only in the matrix area of the follicle
at the base of the cortex directly above the follicular
papilla. Eumelanin is the main pigment found in
black/brown hair and pheomelanin is the predominant
pigment found in blond/red hair. The hair shaft
documents the history of the cosmetic practices of an
individual.
Hair colouring is a procedure commonly used by both
elderly people to conceal their grey hair and youth to
achieve a new fashionable colour shade.
A wide variety of natural and synthetic hair-colouring
agents is available. Vegetable and metallic dyes are
natural colourants, but these have largely been replaced
by synthetic dyes. Hair dyes can last longer on
chemically treated hair as this hair is porous and
unexpected colours can result on chemically treated hair.1
Hair dyes are classified, non-oxidative and oxidative
dyes. Non-oxidative coloration is further divided into two
groups, temporary and semi-permanent colorants.
Oxidative colouring is also divided into three groups,
permanent, demi permanent and auto-oxidation dyeing.
HAIR FIBRE
Hair consists of a long polymeric structure where peptide
chains are held together by various chemical interactions
such as covalent bonds (disulphide linkage), hydrogen
bonds, ionic and hydrophobic interactions. Among them,
disulphide linkage is particularly important for shaping
the mechanical properties of the hair fibre.2 The hair shaft
is divided into four main distinct structures: cuticle,
cortex, cell membrane complex (CMC) and the medulla.3
The cuticles are the most external part of the hair strand
and keep its physical properties. They regulate the
adsorption and diffusion of various active ingredients
during bleaching, dyeing and hair treatments. It contains
six to ten layers of overlapping cells and each cuticle cell
contains an external thin membrane formed by a layer of
fatty acid, responsible for the hydrophobic character of
the fiber.4
DOI: https://dx.doi.org/10.18203/issn.2455-4529.IntJResDermatol20211721
Department of Dermatology, Marsleeva Medicity, Pala, Kerala, India
Received: 21 March 2021
Accepted: 13 April 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.
ABSTRACT
Hair is an important part of body and a major factor in self-image. A wide variety of hair cosmetic preparations are
available and are used regularly by most of the world’s population. Hair colouring is one of the commonly done
procedure. However, any chemical treatment, normal grooming habits and environmental exposure can produce
changes in hair texture or hair breakage. It is necessary for a dermatologist to know the basis of hair colouring, the
procedure and the possible side effects it can cause. Also post colour care is also to be known about to prevent further
damage to treated hair. This article explains the basic chemistry and mechanism involved in hair dyeing and the basic
facts a dermatologist should know.
Keywords: Hair colouring, Paraphenylenediamine, Bleaching, Hair dye, Allergic contact dermatitis

George NM et al. Int J Res Dermatol. 2021 May;7(3):496-502
International Journal of Research in Dermatology | May-June 2021 | Vol 7 | Issue 3 Page 497
The cortex forms the matrix where other proteins and
keratin are located, and composes the larger part of the
fibrous mass of human hair. They consist of cells filled
with keratin and provides mechanical properties to the
fibers.5 The cortical cells, adjacent to the cuticle, are
flatter and contain less sulphur than the cells inside the
cortex, which are rich in cystine, amino acids, lysine and
histidine, in addition to the melanin granules.6 The
consequently lower amount of disulphide crosslinks
leaves non-keratinous proteins more labile and less
resistant to chemical attack than the cystine rich
keratinous components of the fibre.7
The matrix comprises the major structure of the hair and
contains a high concentration of disulphide bonds. It
presents considerable swelling when in contact with
water. It exhibits keratin macro-fibrils aligned in the
direction of the hair strand and melanin granules which
are responsible for the hair colour and its photo
protection. The CMC consist of cell membranes and
adhesive material that “glue” or link the cortical and the
cuticle cells. Chemically, CMC is composed of proteins,
polysaccharides, and ceramides. It is also responsible for
the hair’s natural moisture, making it bright, transparent,
and hydrated.
The medulla is the innermost region and its presence
along the hair is usually discontinuous or even absent and
does not interfere with the hair structure.7 The medulla
can be empty or filled with sponge keratin and has high
lipid concentration, can serve as a pigment reservoir, and
can contribute to the brightness of the hair.
TYPES OF HAIR COLOURING
Hair dying systems can be divided into two main
categories, oxidative or non-oxidative, and also according
to the colour durability after the application on hair
strands: temporary, semipermanent, demi permanent and
permanent.
Temporary hair colour
They are non-oxidative dyes, with high molecular weight
and get deposited on the hair surface post colouring. As
there is no oxidising agent, it doesn’t penetrate the cortex.
They are anionic and hence highly water soluble and can
be removed easily in first shampoo wash. It doesn’t
bleach the hair and hence if the original hair colour is
black, it is not usually seen and they do not have the
power of whitening the hair strand. Because of high
molecular weight, it covers only 15% of grey hair. These
formulas are easy to use and carry little risk of contact
dermatitis. However, these dyes readily stain the scalp
and skin. The temporary non-oxidative formulations as
single applications, present higher dye concentrations,
ranging from 0.1% to 2.0% (w/w) and have the purpose
of promoting a stronger dyeing effect. The formulation
must get in contact with hair for about 30 min and results
will occur immediately. It is suitable for those who wish
for fantasy colors. It resists from three to six washes
when applied to bleached hair, like semipermanent
dyeing. They are available in powder, shampoos and
crayon formulation
Semi-permanent hair dye
They do not use oxidising agents like hydrogen peroxide.
These formulations contain basic or cationic dyes with
low molar mass, which has a high affinity for hair keratin
and resists from three to six washes. Semi-permanent
dyes consist of nitro aromatic amines or aromatic nitro-
anthraquinone dyes that diffuse into the hair and bind to
the hair, however do not attach firmly. Semi-permanent
hair dyes are generally applied to freshly shampooed hair
and allowed to remain on the hair for approximately 10-
40 minutes and the hair is then rinsed with water. The
product usually contains nitro-aromatic molecules
sometimes mixed with inorganic pigments under neutral
or slightly alkaline pH conditions. They penetrate slightly
in the cortex, especially because of the high pH value of
the product promotes the cuticles opening.8 They last for
5-6 shampoo washings and thus require a reapplication.
They are, however, unable to lighten hair as they do not
contain any bleach. Several products are available in the
market: lotions, shampoos, mousses and emulsions.
Cosmetic forms must have the ideal viscosity so that they
do not flow during the application. These semi-permanent
dyes have the potential to cause allergic contact
dermatitis. They cause only minimum hair damage as it
does not involve any harsh chemical processing.
Demi permanent hair dyes
They are more resistant to shampooing when compared to
the semi-permanent dyes. They are applied with
hydrogen peroxide or other demi permanent hair products
are resistant for up to 20 washes because they consist of a
mix of semipermanent molecules with oxidation dye
precursors, applied with hydrogen peroxide (H2O2). In
demi-permanent dyeing, melanin is bleached to a lesser
extent. This product utilises a small amount of mono-
ethanolamine as an alkaliser to get a pH level of 7-8.
Because it doesn’t involve high level of melanin
bleaching, it may offer superior hair quality. However, it
gives very few colour shades and exhibits poor colour
retention.
Permanent hair dyes
Majority in the market belong to this category. They
cover up to 100% of white hair strands. Also, it is
possible to have dark and light natural hair colour due to
the combination of the oxidizing agents with the
ammonia hydroxide.1 They cause permanent dyeing,
resistance to shampoo washes and other external factors,
such as drying, friction, light, and others. The principal
difference between the demi permanent hair dye in
comparison with a permanent one is the alkalizing agent
used because, in the first, mono-ethanolamine with low

George NM et al. Int J Res Dermatol. 2021 May;7(3):496-502
International Journal of Research in Dermatology | May-June 2021 | Vol 7 | Issue 3 Page 498
color lightening power is used.9 Permanent dyes have the
potential to damage the hair shaft. They utilize a series of
chemical processes within a single application and all
forms must be mixed with hydrogen peroxide before
application, without which they are ineffective. The
active ingredients penetrate the hair first and then react to
form a new chromophore inside hair fibre.
FORMULATION OF HAIR DYE
The colour formation is based on a series of oxidation
and coupling reactions and require four major
components: the coupling bases; the reaction modifiers;
an alkalizing compound; and an oxidizing agent.
Coupling bases
Bases are aromatic compounds derived from benzene,
substituted by at least two electron donor groups such as
NH2 and OH in para or ortho positions for easy oxidation,
acting as a colour developer.10
Reaction modifiers/couplers
The modifiers are aromatic m-phenylenediamines,
resorcinol, naphthol and other derivatives.11 They are
aromatic compounds derived from benzene and
substituted by groups such as NH2 and OH in the meta
position, which does not present easy oxidation by H2O2.
They do not produce significant colour alone yield only
feeble colouring through oxidation but can modify them
when used with primary intermediaries and oxidants.10
determine the final shade of the colour after reaction with
the oxidized form of the primary intermediate. Hydrogen
peroxide oxidises the primary to a highly electrophilic
intermediate which then couples with the coupler.
Alkalizing compound
This is necessary to promote the proper pH value for the
beginning of the oxidation reaction. The most commonly
alkalizing compounds used are ammonia (as ammonium
hydroxide) and mono-ethanolamine (MEA) when the
formulation contains water, or sodium silicate when it is
in solid form (powder). When ammonia helps to remove
the natural pigments present in hair as the melanin and in
coverage of 100% of white hairs. After the formation of
the coloured polymer in inner of cortex, its complete
removal is not possible and hence its permanent.
However, MEA does not oxidize melanin. Thus, products
containing MEA instead of ammonia hydroxide are
suitable for maintenance of similar shades or to dark
hair.12
Oxidising agents
There are basically two types of oxidants used: hydrogen
peroxide, when the vehicle is water, and sodium
persulfate, when it is a powder.
Reducing agents
Reducing agents are added to oxidative dye formulations
to retard the reaction between bases and reaction
modifiers and to prevent the initiation of the reaction in
the packaging tube during the storage time. e. g., sodium
metabisulfite (MBS).
Antioxidants
Antioxidants are necessary to avoid the reaction
beginning before the addition of the oxidant itself. A
water-soluble antioxidant can prevent the manipulation of
bases and initiation of oxidative reaction by reaction
modifiers, which may interfere with the final colour of
the product. E. g., erythorbic acid (AEB). An oil-soluble
antioxidant is used as a vehicle for emulsion hair dyes
because this avoids the yellowing of wax and the
oxidation of bases and reaction modifiers. e.g., T-butyl
quinone (TBQ).12
Vehicles
The oxidative dye is available as emulsion (most
commonly used), gels, solutions (liquid), and powders.
Others
The peroxides are very unstable, requiring the use of
stabilizers such as sodium stannate and the penta sodium
pentetate. A mixture of surfactants and solvents is used to
disperse dye molecules and ensure hair wetting.
Categories of contents commonly seen in hair dye (Table
1).
HAIR COLOUR FORMATION
To achieve a shade closer to hair colour, a single step
process of hair dyeing is only needed. To achieve a light
shade, a two-step process is done; bleaching with
hydrogen peroxide and ammonium and potassium
persulphate, and then dyeing is done.
Hair bleaching: It is commonly used by both elderly
people to conceal their grey hair and youth to achieve a
new fashionable colour shade. It is believed that the
bleaching process begins with the gradual solubilisation
of the melanin in hydrogen peroxide at high pH which
may detach pigment grains from the hair proteins. The
dissolved melanin is fairly easily broken down or
depolymerised to carboxylate derivatives that are
removed on rinse off.13,14 Bleaching can also lead to
oxidation of protein components of the hair fibre.
Oxidation of cystine cleaves disulphide linkage
generating cystic acid. This alters the electrostatic
properties of fibre and creates anionic sites which can
subsequently lead to higher metal uptake. As the
disulphide bond contributes to the tensile properties of
the fibre, its cleavage leaves hair fragile and damaged.15

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International Journal of Research in Dermatology | May-June 2021 | Vol 7 | Issue 3 Page 499
Bleached hairs showed apparent breaking and fracturing
from the leading edge in the cuticle’s scales. When the
bleached hairs are re-treated with the bleaching agent, the
cuticles were not only lifted but also removed from the
hair surface. This is why bleached hair fibres present low
tensile strength, high porosity and poor sensorial
profile.16,17
Table 1: Categories of contents in hair dye.
Oxidising
agents
Hydrogen peroxide
Reducing
agents
Sodium metabisulfite (MBS)
Stabilizers
Sodium stannate and the penta sodium
pentetate
Alkalizing
compound
Ammonia (as ammonium hydroxide)
and monoethanolamine (MEA)
Couplers
phenols, meta disubstituted
phenylenediamines and
phenyleneaminophenols, and various
resorcinol (1,3-dihydroxybenzene)
derivatives
Dyes
O-nitro anilines (gives yellow and
orange shades), aminonitrophenols
and their ethers (gives yellow and
orange shades), Azo dyes (gives
yellow and orange shades),
nitrodiphenylamines (gives 'orange to
red shades), nitrophenyienediamines
(gives colour in the range red to
violet), anthraquinone (Gives violet to
blue shades).
Preservatives
Parabens, phenoxyethanol
Phot-
Oprotectors
Homoxalate, Octinosate, Octocrylene,
Oxybenzone
Surfactants
Sodium lauryl sulfate (SLS), sodium
laureth sulfate (SLES), disodium
laureth sulfosuccinate (DSLESS),
disodium lauryl sulfosuccinate
(DSLSS), capramidopropylbetaine,
sodium lauroyl methyl isethionate
(SLMI), cocamidopropyl betaine
(CAPB), capryl/capamidopropyl
betaine, sodium cocoamphoacetate
Emulsifiers
Oleth-23, cetaryl alcohol
Additives
Fragrance, avocado oil, sunflower oil,
olive oil, Dimethicone (conditioning
agent)
Solvents
Quaternium-80, benzyl alcohol, and
glycols
During the permanent dyeing process, the mixture
containing the primary intermediate (e. g., p-
phenylenediamine) and the coupling agent (e.g.,
resorcinol) in alkaline medium (ammonia) is mixed with
a hydrogen peroxide solution forming a paste with pH 9,
5. The mixture is applied to the hair and the precursors
and hydrogen peroxide diffuse into the hair strand, where
after specific chemical reactions a coloured compound
with a high molar mass is formed. The first step is the
oxidation of primary to give a reactive intermediate.
Under alkaline conditions in the presence of hydrogen
peroxide, p-phenylenediamine is oxidised to give quinone
diimine (QDI+). They react with the coupler, form the
leuco dye (colourless). This is converted into the
indoaniline dye within the hair strand. The intermediate
compounds have similar sizes and, therefore, an easy and
uniform penetration occurs inside the hair.18 The hair
surface in untreated hair has a pH of 4.5 to 5.5. This
acidic pH helps to keep the cuticular cells closely
opposed to the cortex.19 The reaction occurs in an
alkaline medium that promotes the opening of the cuticles
that allows the penetration of the dyes’ molecules into the
cortex. Primaries are oxidised inside the hair to give
reactive intermediates which then react with the couplers.
This reaction yields a new chromophore imparting a new
colour shade to the fibre. The new chromophore is bigger
in size than the starting precursors and thus cannot
diffuse out of the fibre easily. Part of the reaction also
happens on the cuticles and the molecules are removed in
the first washes. In the absence of a coupler, oxidation of
the intermediate can form coloured polynuclear
compounds generated by the reaction between the
diimine and the original amine forming Bandrowski base.
Beside oxidation of dye precursors, hydrogen peroxide
bleaches naturally occurring melanin pigment inside hair
fibre and its decomposition products are subsequently
removed during rinse off.
Various parameters may affect the colour formation in
the hair dyeing process, such as pH, pause time, hair
keratin, and purity of the dye molecule, amongst others.
The variation of the pH value directly influences the
reaction rate because a more alkaline pH favours the
reaction and facilitates the cuticle opening, allowing the
penetration of molecules into the cortex.
The pause time is essential for a complete reaction
between the bases and reaction modifiers to occur.
According to the manufacturer’s guidelines, the product
must be in contact with the hair from 30 to 45 min after
application because it is then possible to ensure colour
reproduction and durability to washing.
There are other permanent hair-dye products which
produce progressive hair colouration (by reacting with
the sulphur of hair keratin) which are not formulated with
oxidative hair dyes. They produce gradually a darkening
of the hair. Lead acetate and bismuth citrate act as active
ingredients in this type of products.20
OTHER HAIR DYES
A number of herbal and ayurvedic dyes are available in
India under various trade names such as Black Rose hair
dye herbal, optima hair dye, khadi dye, vegetal etc.
Though they claim herbal, many of them warrant for a
sensitivity test prior to application and allergies have
been noticed after application of the same.

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International Journal of Research in Dermatology | May-June 2021 | Vol 7 | Issue 3 Page 500
Henna (Lawsonia alba), is a natural organic substance,
and is the most widely used vegetable dye for hair,
providing reddish orange shades. In some commercial
products, it is mixed with other dyes to increase the range
of colour. It consists of the dried leaves of the Lawsonia
alba plant. Its colouring properties are due to the presence
of the substance 2-hydroxy-1,4-naphthoquinone. Natural
henna is mixed with tea water or coffee water overnight
to make the colour more visible. Indigofera tinctoria is a
natural dye that is available for commercial use as a green
powder. It is mixed with water and applied the same way
as henna; When mixed with henna, the colour results are
superior.
Other natural dyes from walnut or logwood are used in
Asian counties to blacken greying hair. Metallic dyes
using the salts of silver, lead or bismuth were
traditionally used by men, as the colour change occurs
gradually and use is limited to darkening the hair.21 The
metals are thought to interact with cysteine in the cuticle
to form metal sulphides and the deposits gradually
accumulate on the cuticle producing brittle, dull hair.
SIDE EFFECTS OF HAIR DYE
Hair colouring is a commonly done procedure; though
not investigated fully, it is associated with a lot of side
effects. Airborne contact dermatitis, irritant contact
dermatitis, photo contact dermatitis, periorbital eczema,
hand eczema, lichenoid lesions, and lichen planus
pigmentosus-like pigmentary changes were the
commonly observed clinical patterns of hair dye
dermatitis. Paraphenylenediamine (PPD) is the major
culprit responsible for most of the adverse effects.
Contact leukoderma, contact urticaria, lymphomatoid
papulosis, erythema multiforme-like or prurigo nodular
is-like lesions, and anaphylaxis have also occurred with
PPD.22-26 PPD intoxication results in multisystem
involvement and can cause rhabdomyolysis and acute
kidney injury (AKI), flaccid paralysis, severe gastro-
intestinal manifestations, cardiotoxicity and
arrhythmias.27 There are reports of increased risk of
bladder carcinoma in women who use permanent dyes
frequently and for long periods.28 However, a case-
control study conducted at a hospital in Spain with more
than 300 women did not show an increased risk of
developing bladder cancer related to the regular use of
hair dyes.29 It is also mentioned that use of permanent
dyes can have a relevant impact on the risk of developing
acute leukemia in adults.30 Some dermatological and/or
carcinogenic side-effects have been attributed to some
chemicals used as hair dyes.31 Taylor et al described four
cases of leukoderma caused by hair colors.32 In most of
these cases, the cause of selective melanocytotoxicity is
PPD, and depigmentation at patch test sites has also been
reported after a few months of testing.33 Primary
sensitisation can be from sources other than hair dye.
Today, PPD is permitted in the European union at a
concentration of 6% and toluene-2,5-diamine is permitted
at a concentration of 10%.34
IF ALLERGIC TO PPD
A patch test is recommended. Dyes containing para-
toluenediamine sulphate (PTDS) may be an option found
in newer semi-permanent and permanent dyes and up to
50% may be able to tolerate it.35
Open test: On a clean area behind the ear or on the
forearm just below the elbow, the dye mix is applied with
a cotton swab and allowed to dry. If there is no reaction
in 48 to 72 hours, the dye mix can be safely used on the
scalp.
Another hair colouring method has been followed by
many, who are allergic to normal hair dye, includes,
application of henna leaf paste (mixed with tea/coffee
water and lemon juice) for 45-60 min followed by rinsing
and then treating the hair with indigo powder paste
(powder mixed in warm water) for few hours followed by
rinsing. This gives a shade similar to black if done
repeatedly. But indigo can stain hands and scalp, hence it
is advised to apply only on hair shaft.
STYLES IN COLOURING
Highlighting is a process by which isolated sections of
hair are either lightened or darkened. This is done by the
‘foil method,’ where strands of hair are separated by a
comb and laid over an aluminium foil sheet, and then
painted with a mixture of hydrogen peroxide and
pigment. The foil is then folded, and the contact time
depends upon the shade required.
Dip dyeing where only the tips of hair is dyed. Ombré is
when a gradually increasing shade is applied from
proximal to distal end of hair shaft.
POST COLOURING CARE
Shampoos with cationic surfactant is preferred post
colouring.19 It is mandatory to use conditioners as they
flatten the cuticles and seal the gaps that could expose the
important cortex to environmental damage. Choosing the
right surfactant system and conditioning agents are
important for reducing the colour fade. Significantly
faster colour fading was observed for sodium lauryl
sulphate and sodium lauryl sulphate (surfactants).
Sulphate-free surfactants showed statistically significant
advantages for colour protection shampoos. A
combination of silicone quaternium-22 microemulsion
and silicone UV quat (poly-silicone-19) visibly improves
the colour protection of shampoo formulations. An
increasing level of Poly-silicone-19 correlates with
increasing colour protection. An effective colour
protection shampoo should be based on mild surfactants,
conditioning agents for improved combability and feel of
the hair and UV-filters for protection against fading
induced by UV light.

George NM et al. Int J Res Dermatol. 2021 May;7(3):496-502
International Journal of Research in Dermatology | May-June 2021 | Vol 7 | Issue 3 Page 501
To prevent serial fading of hair dye post colouring, it was
found that polymers with hydrophobically modified and
cationic functionalities are most effective in preventing
hair dye dissolution in water. A primary example of a
polymer within this category is a cationic terpolymer of
vinylpyrrolidone, dimethylaminopropyl methacrylamide,
and methacryloylamino propyl lauryl-dimonium
chloride.36
CONCLUSION
Hair colouring is getting common these days and people
want to look young and trendy. However, it is associated
with structural and systemic side effects. Hence, more
developments should come in the field of hair colour to
prevent the side effects and reduce structural side effects.
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. Hair
colouring: what a dermatologist should know? Int J
Res Dermatol 2021;7:496-502.