In this article about hair dye products, you will learn everything there is to know about hair dyes, including: how they work, the ingredients which make it all work, the different types of hair dying products, their formulation, regulation and claims.
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Mechanism of Action of Hair Dye
Step 1: Open Cuticle
The first step in the hair dyeing process is to open the cuticle layer of the hair. The cuticle, which is the outermost protective layer of the hair shaft, is composed of overlapping scales that lie flat in healthy hair. To achieve this, alkaline agents, typically ammonia or an ammonia substitute, are used in the dye formulation. These agents work by raising the pH of the hair, which in turn causes the cuticle scales to lift, creating openings in the hair shaft. As a result, the hair becomes more porous, thereby allowing the dye to penetrate deeper into the hair structure. Opening the cuticle is crucial for the dyeing process because it allows the hair dye to reach the cortex, where the natural pigment (melanin) is located and where colour changes occur.
Step 2: Remove Melanin/Existing Dye
Once the cuticle is open, the next step involves removing or lightening the natural melanin (the hair’s natural pigment) or existing dye in the hair. Hydrogen peroxide, also known as a developer, is used as an oxidising agent. It works by breaking down the natural melanin or existing dye molecules in the cortex. If there is existing dye in the hair shaft, these can be removed by reducing agents which help break down the dye structures to be easily washed out. Removing or lightening the natural pigment is essential for achieving the desired hair colour, especially if you’re going from a darker shade to a lighter one or covering up an existing dye.
Step 3: Add Dye
With the cuticle open and the natural pigment lightened, the hair is ready to receive the new colour. The hair dye, which contains direct dye molecules, is applied to the hair. These molecules are initially small enough to penetrate the cortex through the lifted cuticle. Once inside the cortex, the dye molecules undergo a chemical reaction (often oxidation) that causes them to expand and develop into larger, permanent dye structures that bond with the hair. Adding the dye at this stage allows the colour to be deposited deep within the hair, ensuring that it is vibrant and long-lasting. The new colour bonds with the hair structure, making it resistant to washing out.
Step 4: Close Cuticle
After the colour has been deposited, the final step is to close the cuticle to protect the hair and lock in the new colour. The dyeing process usually concludes with a conditioning treatment or a pH-balancing product that helps to lower the hair’s pH, causing the cuticle scales to flatten and close. Closing the cuticle seals the colour inside the cortex and smooths the hair surface, giving it a shiny and healthy appearance. Closing the cuticle is essential for maintaining the integrity of the hair, preventing damage, and ensuring that the colour stays vibrant for as long as possible.
Image cutrosy of lab muffin.
Hair Dye Product Types
Permanent Hair Dye
Permanent hair dye is formulated to penetrate the hair shaft deeply and alter the natural pigment (melanin) within the hair. It typically contains ammonia or an ammonia substitute and hydrogen peroxide as key ingredients.
- Ammonia (or substitute): Opens the cuticle layer of the hair, allowing the dye to penetrate the cortex where the natural pigment resides.
- Hydrogen Peroxide: Lightens the natural colour of the hair, providing a base for the new colour to be deposited. The peroxide also acts as an oxidising agent, helping the dye to develop and bond to the hair structure.
- Dye Molecules: These are small when they enter the hair but expand as they react within the cortex, becoming too large to wash out easily, which makes the colour long-lasting.
Permanent dyes are long-lasting and typically remain in the hair until it grows out or is cut off. They resist washing and fading due to the deep penetration and bonding of the colour molecules within the hair shaft. Ideal for covering grey hair, achieving significant colour changes, and creating vibrant, long-lasting hair colours.
Temporary Hair Dye
Temporary hair dye coats the outside of the hair shaft with colour rather than penetrating it. These hair dye products contain larger colour molecules that do not enter the cortex, meaning they simply adhere to the surface of the hair. Because they do not alter the hair’s natural pigment, they provide colour that can be easily washed out. Temporary dyes often come in the form of sprays, gels, mousses, or rinses and are designed for quick and easy application.
Temporary hair dye washes out with one shampoo or gradually fades after a few washes. The colour does not last as long because it does not chemically bond with the hair. Ideal for short-term changes, special occasions, or experimenting with different colours without commitment. Temporary dyes are also less damaging to hair since they do not require strong chemicals.
Hair Dye Shampoos/Semi Permanent Dye
Hair dye shampoos, also known as colour-depositing shampoos, work by gradually depositing colour onto the hair each time the shampoo is used. These hair dye products contain small amounts of direct dye molecules that adhere to the hair’s surface and sometimes slightly penetrate the outer cuticle. They also often contain conditioning agents to help smooth and protect the hair during the colouring process.
The colour effect is typically semi-permanent, meaning it lasts longer than temporary dyes but not as long as permanent dyes. The colour gradually builds with each use and fades when you stop using the product. Ideal for maintaining or enhancing colour between dye jobs, adding subtle tints or hues to the hair, or creating a gradual colour change over time. Hair dye shampoos are also used for toning purposes, such as neutralising brassiness in blonde hair.
Hair Bleach
Hair bleach works by a process called oxidation, which breaks down the natural pigments in the hair, primarily melanin. Hair bleach is usually a combination of a strong alkaline agent like ammonium hydroxide (to first open the cuticle) and an oxidizing agent, most commonly hydrogen peroxide.
Once inside the cortex, hydrogen peroxide releases oxygen radicals. These highly reactive molecules break down the molecular structure of melanin through oxidation. Melanin is a complex polymer, and its breakdown results in the lightening of the hair.
The process gradually breaks down darker pigments first (eumelanin), and then the lighter pigments (pheomelanin). This is why hair often turns an intermediate color, like orange or yellow, before reaching a light blonde or near-white shade. The extent of color change depends on the concentration of the hydrogen peroxide, the processing time, and the natural color of the hair. This oxidative process can damage the hair structure by breaking down keratin bonds, leading to dryness and brittleness.
Ingredients in Hair Dye Products
Alkali Agents (Open the Cuticle)
Alkali agents, such as ammonia or monoethanolamine (MEA), are used to raise the pH of the hair dye formula. By increasing the pH, these agents cause the cuticle (the outermost layer of the hair shaft) to lift and open. This is crucial because it allows the dye and other chemicals to penetrate deeper into the hair’s cortex, where the natural pigment (melanin) and any existing dye are located.
Chemical structure of monoethanolamine (MEA)
Reducing Agents (Remove Dye)
Reducing agents are used in dye-removal products such as sodium thioglycolate. These agents work by breaking the chemical bonds within the artificial colour molecules, effectively reducing them into smaller components that can be washed out of the hair. They target the artificial dye molecules without significantly affecting the hair’s natural pigment.
Chemical structure of sodium thioglycolate
Oxidising Agents (Remove Melanin)
Oxidising agents, such as hydrogen peroxide, are used to remove or lighten the hair’s natural pigment (melanin). These agents work by oxidising the melanin in the hair’s cortex, breaking it down and lightening the natural colour. This creates a base, allowing the new hair colour to show up more vividly and accurately.
Chemical structure of hydrogen peroxide
Direct Dyes (Deposit Dye Onto Hair)
Direct dyes are preformed colour molecules that can deposit colour directly onto or into the hair without needing a chemical reaction. These dyes are generally used in semi-permanent and temporary hair colours. They work by either coating the surface of the hair or penetrating slightly into the cortex, where they adhere to the hair fibre. Direct dyes do not require an oxidising agent to develop and are often used to enhance or refresh colour without causing significant damage. Basic yellow 87 (used in semi-permanent colors).
Chemical structure of basic yellow 87
Reactive Dyes (Deposit Dye Into Hair)
Reactive dyes are the primary colouring agents that chemically bond with the hair’s natural keratin. Unlike direct dyes, reactive dyes contain functional groups that react with the hair’s protein structure, forming covalent bonds. This chemical reaction leads to a long-lasting and durable colour that is resistant to washing and fading. Reactive dyes can create vibrant and permanent colours because they become part of the hair’s structure. Examples include vinyl sulfone dyes, chlorotriazine dyes.
Chemical structure of vinyl sulfone dyes
Precursor & Coupler Dyes (Deposit Dye Into Hair)
Precursors are small, colorless pigment molecules that penetrate the hair shaft and transform into visible color when oxidized by hydrogen peroxide. Examples include p-phenylenediamine (PPD), p-toluenediamine (TDA), and para-aminophenols.
Coupler molecules interact with the oxidized precursors to establish the final hair color shade. Common couplers include resorcinol, chlororesorcinol, methyl resorcinol, α-naphthol, m-aminophenol, and m-phenylenediamine.
Chemical structures of PPD & methyl resorcinol
Cationic Surfactants (Close the Cuticle)
Cationic surfactants such as behentrimonium chloride are positively charged molecules used in hair care products to condition and smooth the hair. After the hair dyeing process, cationic surfactants help to neutralise the hair’s pH and close the cuticle layer. By closing the cuticle, these agents help to lock in the new colour, making it more resistant to washing out and leaving the hair smoother and shinier. They also provide conditioning benefits, reducing static and tangling, and making the hair easier to manage.
Chemical structure of behentrimonium chloride
Formulation of Hair Dye Products
Hair Bleach - Paste
Ingredient | Maximum concentration (% w/w) |
Persulfates | 70 |
Oils | 60 |
Bulking agents | 50 |
Alkaline agents | 45 |
Emulsifying agents | 15 |
Thickeners | 10 |
Additional ingredients | 5 |
Ingredient Types And Functions In hair bleach
Persulfates – 70%
These persulfate salts are the primary bleaching agents that break down the natural melanin in hair, lightening its colour. They generate free radicals when mixed with water or hydrogen peroxide, which then break down the colour molecules in the hair. Examples: ammonium persulfate, sodium persulfate, potassium persulfate.
Oils – 60%
Oils in hair bleach formulations help to condition the hair and protect it from the harsh effects of bleaching. They reduce damage, add moisture, and improve the hair’s overall texture during the bleaching process. Examples: coconut oil, argan oil, mineral oil.
Bulking Agents – 50%
Bulking agents increase the volume of the bleach mixture, making it easier to apply evenly throughout the hair. They also contribute to the consistency of the product, ensuring it is neither too runny nor too thick. Examples: silica, kaolin clay, starch.
Alkaline Agents – 45%
Alkaline agents raise the pH of the hair bleach, which helps to open the hair cuticle, allowing the bleaching agents to penetrate the hair shaft more effectively. This enhances the lightning process. Examples: sodium, magnesium silicate, sodium carbonate, sodium metasilicate, ammonium chloride.
Emulsifying Agents – 15%
Emulsifiers help to mix oil-based and water-based ingredients in the bleach, creating a stable and uniform product. They ensure that the bleach applies smoothly and evenly to the hair. Examples: cetearyl alcohol, glyceryl stearate, polysorbate 60, sodium lauryl sulfate.
Thickeners – 10%
Thickeners adjust the viscosity of the bleach mixture, making it easier to control during application. They prevent the bleach from dripping and ensure it stays in place on the hair. Examples: xanthan gum, carbomer, hydroxyethylcellulose.
Additional Ingredients – 5%
This category includes a variety of functional additives that enhance the bleach’s performance, improve its stability, or provide additional benefits like conditioning or fragrance. Examples: fragrance (parfum), conditioning agents like panthenol, chelating agents like EDTA to stabilise the formula.
Dye remover (reducing agent) - part a (to be mixed with part b)
Ingredient | Maximum concentration (% w/w) |
Acid | 13 |
Aqua | to 100 |
Ingredient Types And Functions In dye remover (a)
Acid – 13%
Acids are used to break down dye molecules which are already present in the hair. Example: citric acid.
Water – to 100%
Main solvent to dilute the acid.
pH value: 1.5 – 2
Dye remover (reducing type) part b (to be mixed with part a)
Ingredient | Maximum concentration (% w/w) |
Reducing agent | 20 |
Aqua | to 100 |
Ingredient Types And Functions In dye remover (b)
Reducing agent – 20%
Reducing agents help to break the disulfide bonds in the hair which help release the hair dye locked in strands. Examples: sodium thioglycolate
Water – to 100%
Main solvent to dilute the acid.
pH value: 10 -11
Hair Colourant (permanent, oxidative type) part a
Ingredient | Maximum concentration (% w/w) |
Alkaline agents | 22 |
Solvents | 20 |
Hair dyeing agent: primary intermediates | 10 |
Hair dyeing agent: couplers | 10 |
Directs (Colourants) | 10 |
Ethanol, isopropanol (alcohol, alcohol denat., isopropyl alcohol) | 16 |
Thickeners | 10 |
Cationic surfactants | 5 |
Cationic polymers | 5 |
Additional ingredients | 5 |
Antioxidants, reducing agents | 3 |
Parfum | 2 |
Chelating agents | 1 |
Aqua | to 100 |
Ingredient Types And Functions In permanent hair dye (a)
Oxidative part with a pH of 8-11.
Alkaline Agents – 22%
Alkaline agents open the hair cuticle to allow the dye to penetrate the hair shaft. They are essential for enabling the chemical reaction between the hair dyeing agents. Ammonium hydroxide, monoethanolamine (MEA).
Solvents – 20%
Solvents dissolve other ingredients in the formulation, ensuring even application and consistency.Examples: Water (aqua), alcohol, propylene glycol, glycerin.
Hair Dyeing Agent: Primary Intermediates – 10%
These are the colour precursors that react with couplers and oxidizers to form the final dye molecule that colours the hair. Examples: p-phenylenediamine (PPD), toluene-2,5-diamine, p-aminophenol, 4-amino-m-cresol, 1-hydroxyethyl 4,5-diamino pyrazole sulfate.
Hair Dyeing Agent: Couplers – 10%
Couplers react with primary intermediates to create the desired shade of hair colour. They determine the tone and depth of the final colour. Examples: Resorcinol, m-aminophenol, 4-amino-2-hydroxytoluene, 2-amino-4-hydroxyethylamino-anisole, 4-chlororesorcinol, 2,6-dihydroxy-3,4-dimethylpyridine, 1,5-naphthalenediol.
Directs (Colourants) -10%
Direct dyes are preformed colour molecules that deposit directly onto the hair shaft without the need for chemical reactions. They provide vibrant colours but typically wash out more quickly. Examples: basic blue 99, basic red 76, 3, 2-amino-6-chloro-4-nitrophenol, basic yellow 87.
Ethanol, Isopropanol – 16%
These alcohols act as solvents and can also help in drying the hair dye faster on application.
Examples: Ethanol, isopropyl alcohol.
Thickeners – 10%
Thickeners give the dye its desired consistency, making it easier to apply and stay in place on the hair. Examples: Carbomer, xanthan gum.
Cationic Surfactants – 5%
Cationic surfactants condition the hair and improve the texture, making it feel softer and more manageable after dyeing. Examples: Cetrimonium chloride, behentrimonium chloride, dicetyldimonium chloride, PEG-2 oleamine.
Cationic Polymers – 5%
These polymers enhance conditioning, provide smoothness, and help in better dye deposition on the hair. Examples: polyquaternium-10, polyquaternium-6, guar hydroxypropyltrimonium chloride.
Additional Ingredients – 5%
These can include a variety of additives that enhance the performance, stability, or sensory properties of the dye. Examples: UV filters, preservatives, conditioning agents, pearlescent agents.
Antioxidants, Reducing Agents – 3%
Antioxidants prevent the dye from oxidising prematurely, while reducing agents are involved in the chemical process of dye formation. Examples: Ascorbic acid, sodium metabisulfite.
Parfum -2 %
Parfum adds fragrance to the dye, masking the often strong odour of the chemical ingredients. Examples: Fragrance blends, essential oils.
Chelating Agents – 1%
Chelating agents bind to metal ions in the water or formulation that could otherwise interfere with the dyeing process or cause the colour to fade. Examples: EDTA (ethylenediaminetetraacetic acid), tetrasodium EDTA.
Aqua – to 100%
Water is the base solvent that dissolves other ingredients and helps in the overall consistency and application of the dye.
Hair Colourant (permanent, oxidative type) part b
Ingredient | Maximum concentration (% w/w) |
Emulsifying agents | 20 |
Anionic surfactants, amphoteric surfactants, non-ionic surfactants | 20 |
Emollients, humectants | 20 |
Thickeners | 20 |
Cationic surfactants | 5 |
Additional ingredients | 5 |
Parfum | 2 |
Chelating agents | 1 |
Oils | to 100 |
Ingredient Types And Functions In permanent hair dye (b)
Emulsifying Agents – 20%
These surfactants help to form stable emulsions by reducing surface tension between ingredients like oils and water. Examples: Glyceryl stearate, cetearyl alcohol.
Anionic Surfactants, Amphoteric Surfactants, Non-Ionic Surfactants – 20%
These ingredients are cleansing agents which help to get rid of excess dye. Examples: Sodium lauryl sulfate, sodium laureth sulfate, Cocamidopropyl betaine, Polysorbate 20, decyl glucoside.
Emollients, Humectants – 20%
Emollients soften and smooth the hair, while humectants attract and retain moisture, preventing dryness during and after the dyeing process. Examples: Cetyl alcohol, isopropyl myristate, glycerin, propylene glycol.
Thickeners – 20%
Thickeners give the paste its desired consistency, making it easier to apply and preventing it from dripping during application. Examples: Xanthan gum, carbomer, hydroxyethylcellulose.
Cationic Surfactants – 5%
Cationic surfactants provide conditioning benefits, reduce static, and improve the smoothness and manageability of the hair after dyeing. Examples: cetrimonium chloride, behentrimonium methosulfate, dicetyldimonium chloride, PEG-2 oleamine.
Additional Ingredients – 5%
This category includes a variety of functional additives such as UV filters, stabilisers, or preservatives that enhance the performance, stability, or shelf-life of the product. Examples: phenoxyethanol
Parfum – 2%
Parfum adds fragrance to the product, masking the odour of chemical ingredients and providing a pleasant scent during and after application. Examples: Fragrance blends, essential oils like lavender or citrus.
Chelating Agents – 1%
Chelating agents bind metal ions present in water or the formulation, preventing them from interfering with the dyeing process or causing colour fading. Examples: EDTA (ethylenediaminetetraacetic acid), tetrasodium EDTA.
Oils – to 100%
Oils nourish and condition the hair, add shine, and help to protect the hair shaft during the dyeing process. They also contribute to the emollient properties of the formulation. Examples: Argan oil, coconut oil, jojoba oil.
Semi-permanent hair dye
Ingredient | Maximum concentration (% w/w) |
Ethanol, isopropanol | 50 |
Oils, waxes and fats | 20 |
Emulsifying agents | 11 |
Silicones | 10 |
Anionic surfactants, non-ionic surfactants, amphoteric surfactants | 10 |
Hair dyeing agent: direct dyes | 10 |
Solvents | 10 |
Cationic surfactants | 5 |
Additional ingredients | 5 |
Hair conditioning agents | 5 |
Resins | 3 |
Thickeners | 2 |
Parfum | 1 |
Preservatives, antimicrobials | 1 |
pH adjuster, alkaline | 10 |
Aqua | to 100 |
Ingredient Types And Functions In semi-permanent hair dye
Ethanol, Isopropanol – 50%
These alcohols act as solvents, helping to dissolve other ingredients and allowing the dye to penetrate the hair shaft. They also help in quick drying after application. Examples: Ethanol, Isopropyl Alcohol.
Oils, Waxes, and Fats 20%
These ingredients condition and protect the hair, providing shine and preventing dryness caused by the dyeing process. Examples: coconut oil, jojoba oil, beeswax, mineral oil.
Emulsifying Agents – 11%
Emulsifiers help to blend water-based and oil-based ingredients into a uniform mixture, ensuring even application of the dye. Examples: glyceryl stearate, ceteareth-20.
Silicones – 10%
Silicones provide a smooth, shiny finish to the hair and help protect the hair shaft by forming a barrier. Examples: cyclopentasiloxane dimethicone, amodimethicone.
Anionic, Non-Ionic, and Amphoteric Surfactants – 10%
Function: Surfactants help to clean the hair by removing oils and dirt, allowing for better dye uptake. They also stabilise the formulation. Examples: Sodium laureth sulfate, cocamidopropyl betaine, decyl glucoside.
Hair Dyeing Agent: Direct Dyes – 10%
These are the actual colourants that provide the desired shade. Direct dyes do not require a developer and deposit colour directly onto the hair shaft. Examples: basic blue 99, acid violet 43, HC red no.3, 4-amino-3-nitrophenol, 3-nitro-p-hydroxyethylaminophenol.
Solvents – 10%
Solvents help dissolve the dyes and other ingredients, ensuring even application and stability of the formula. Examples: Propylene glycol, benzyl alcohol.
Cationic Surfactants – 5%
These surfactants help to condition the hair by reducing static and improving manageability, making hair feel softer and smoother. Examples: cetrimonium chloride, behentrimonium chloride, dicetyldimonium chloride
Additional Ingredients – 5%
These include various functional ingredients like colour stabilisers, shine enhancers, or other performance boosters. Examples: plant extracts, anti-static agents.
Hair Conditioning Agents – 5%
Conditioning agents nourish the hair, improving texture and reducing damage from the dyeing process. Examples: hydrolyzed keratin, panthenol, cationic polymers
Resins – 3%
Resins help to hold the colour in place and improve the longevity of the dye by forming a film over the hair shaft. Examples: PVP (polyvinylpyrrolidone), acrylates copolymer.
Thickeners – 2%
Thickeners adjust the viscosity of the product, making it easier to apply and control during the dyeing process. Examples: xanthan gum, carbomer.
Parfum – 1%
Fragrance is added to improve the sensory experience of the product, masking the scent of raw materials. Examples: synthetic fragrance, essential oils.
Preservatives, Antimicrobials – 1%
Preservatives prevent microbial growth, ensuring the product remains safe and effective during its shelf life. Examples: phenoxyethanol, ethylhexylglycerin.
pH Adjuster, Alkaline – 10%
pH adjusters modify the pH of the formulation to optimise the dyeing process and ensure product stability. Examples: sodium hydroxide, monoethanolamine, citric acid, ethanolamine, ammonium hydroxide.
Aqua (Water) – 100%
Water acts as the base and solvent for the formulation, helping to disperse ingredients and adjust the consistency of the product.
Temporary hair dye shampoo
Ingredient | Maximum concentration (% w/w) |
Surfactants | 40 |
Hair conditioning agents | 15 |
Thickeners | 10 |
Additional ingredients | 10 |
Cationic surfactants | 5 |
Hair dyeing agents: directs dyes | 3 |
Preservatives, antimicrobials | 1 |
Parfum | 1 |
Chelating agents | 0.5 |
Aqua | up to 100 |
Ingredient Types And Functions hair dye shampoo
Surfactants – 40%
Surfactants are the primary cleaning agents in shampoo. They help to create foam and remove dirt, oil, and product buildup from the hair and scalp. Examples: sodium lauryl sulfate (SLS), sodium laureth sulfate (SLES), cocamidopropyl betaine.
Hair Conditioning Agents – 15%
These agents help to improve the texture and manageability of the hair. They provide moisturising and softening effects, making the hair feel smoother and more manageable after washing. Examples: panthenol (vitamin B5), dimethicone, behentrimonium chloride.
Thickeners – 10%
Thickeners adjust the viscosity of the shampoo, giving it a desirable consistency for easier application and use. They ensure the product remains stable and effective. Examples: xanthan gum, hydroxyethylcellulose, carbomer.
Additional Ingredients – 10%
This category includes various other components that enhance the shampoo’s performance or add specific benefits, such as special effects, colour enhancement, or improved stability.
Examples: Botanical extracts (e.g., aloe vera), UV filters, Pearlescent agents.
Cationic Surfactants – 5%
Cationic surfactants condition the hair and help detangle it. They are positively charged and work well with negatively charged hair fibres to reduce static and improve softness. Examples: quaternium-80, cetrimonium chloride, polyquaternium-7.
Hair Dyeing Agents: Direct Dyes – 3%
Direct dyes impart colour to the hair temporarily. These dyes adhere to the hair’s surface without requiring a chemical reaction to develop colour. Examples: Blue 1 (CI 42090), Red 40 (CI 16035), Yellow 5 (CI 19140).
Preservatives, Antimicrobials – 1%
Preservatives and antimicrobials prevent the growth of bacteria, fungi, and other microorganisms in the shampoo, extending its shelf life and maintaining product safety. Examples: phenoxyethanol, ethylhexylglycerin, sodium benzoate.
Parfum – 1%
Parfum (fragrance) provides a pleasant scent to the shampoo, enhancing the user’s experience and masking any chemical odours. Examples: Fragrance oils, Essential oils.
Chelating Agents – 0.5%
Chelating agents bind to metal ions (such as calcium and magnesium) in water, preventing them from interacting with other ingredients and affecting the performance of the shampoo. Examples: ethylenediaminetetraacetic acid (EDTA), citric acid.
Regulation of Hair Dye Products
Prohibited Hair Dye Ingredients
Hair dyes and their ingredients have been under scrutiny for many years as many people have developed contact dermatitis when exposed to hair dye ingredients over the years. Systematic exposure to hair dye products, especially if used frequently, has a potential to carry health risks.
Annex II of the EU cosmetic regulation (EC) No. 1223/2009 lists ingredients prohibited in cosmetics and their specific uses. Many ingredients are listed here with the phrase “when used as a substance in hair dye products”.
Safety & Labelling
Hair dye products need to be labelled correctly to ensure consumers are well informed when using hair dye products on themselves or others.
Required for oxidative hair colouring products and on products containing direct hair colouring ingredients that have been classified as having extreme or strong sensitising potential:
Hair colourants can cause severe allergic reactions.
Read and follow instructions.
This product is not intended for use on persons under the age of 16.
Temporary ―black henna tattoos may increase your risk of allergy.
Do not colour your hair if:
— you have a rash on your face or sensitive, irritated and damaged scalp,
— have ever experienced any reaction after colouring your hair,
— experienced a reaction to a temporary ―black henna‖ tattoo in the past.’
Depending on the formulation, this additional warning is commonly used:
Contains [ingredient name].
For professional use only.
Avoid contact with eyes.
Rinse immediately if product comes into contact with them.
Rinse hair well after application.
Wear suitable gloves.
Additional recommended warnings/instructions:
An allergy alert test* or another evaluation should be performed before each product use, even by clients who have already used colouring products before. Remember that the alert test has to be performed 48h before use.
IMPORTANT: This product is not intended for use on persons under the age of 16. Hair colourants can cause severe allergic reactions.
Do not colour if your client:
Avoid contact with eyes. Rinse immediately if product comes into contact with them. Rinse hair well after application. Wear suitable gloves.
Keep out of reach of children.
Cosmetics Europe has published the following guidance documents:
Hair Dye Labelling – Information for Consumers
Hair Dye Labelling – Information for Professionals
Allergy Alert Test for Hair Colouring Products
Post-Market Surveillance
Cosmetics are also regulated after they have been made available to the public through cosmetovigilance. Companies are responsible for collating, analysing, and reporting serious undesirable effects (SUEs) to competent authorities annually. This process is essential for monitoring any potential spikes in adverse health effects to consumers. Consequently, if a concerning trend is identified, it may lead to an inquiry with the Scientific Committee on Consumer Safety (SCCS). The SCCS would then review the data and, based on their findings, suggest that certain ingredients be added to Annex II of the cosmetic regulation.
A causality assessment is performed by the responsible person in the EU/UK to determine whether or not the cause of the undesirable effect was caused by the cosmetic exposure or not. Things to take into consideration are :
- The normal and foreseeable use of the products – if the products are being misused (e.g. using eyeshadow on the lips)
- The customer’s predispositions (history of use).
- The duration of use (e.g. using a rinse-off product intended to be left on for 5 minutes being left on for 30 minutes).
A person who is trained in complaint handling and has an appropriate background should be responsible for conducting the causality assessment. In certain cases, it may be advisable to seek the support of an external or in-house healthcare professional when conducting the causality assessment in order to obtain a high degree of confidence in the result. This should be recorded in the case file documentation and the product information.
According to the method, five levels of causality can be obtained: ‘very likely’, ‘likely’, ‘not clearly attributable’, ‘unlikely’ and ‘excluded’.
Read this guidance document published by Cosmetics Europe about SUEs reporting.
Claims of Hair Dye Products
Non-permitted claims
Reduced Risk of Allergic Reaction
Allergic reactions are highly subjective to each user. Therefore, the history of use, exposure to other potential irritants (not just hair dye products), and frequency of use all need to be taken into consideration. Additionally, since these factors vary significantly from person to person, no company can guarantee the absence of allergic reactions. The risk may be reduced by decreasing the concentration of irritants, but it is not predetermined what concentration of irritant will cause a certain individual to experience an allergic reaction. Safety claims should be avoided as it creates a sense of false security for consumers who have a history of allergic reactions.
Brilliant Blonde Results Every Time
Unfortunately the results of hair dye treatments can not be guaranteed. This is why you often see the potential results of the product on different hair types – but it also doesn’t take into consideration the hair’s treatment history which can influence the final outcome.
Permitted claims
Ammonia Free
We tend to steer-clear of free-from claims, but ammonia free is permitted as specific consumers may have found ammonia to be too strong of an alkali agent and may want to use an alternative or not open their cuticle at all (in the case of non-permanent dye).
Lasts for 6 weeks
This claim can indeed be made; however, there are substantiation challenges associated with it. For instance, lasting claims are often made for non-permanent hair dye products, which will eventually be washed off. Nevertheless, the length of time the dye remains depends on several factors, including the adhesion of the direct dyes to the hair and the strength of the detergents (surfactants) used during shampooing. Typically, repeat tress cleansing tests are performed on dyed hair strands to determine how many washes it takes to observe a significant colour change. While the brand can control the adhesion of direct dyes, it cannot control the strength of surfactants or the frequency of washing, making it difficult to substantiate the claim. Therefore, trials should ideally use conservative values, such as strong anionic surfactants at high concentrations (e.g., SLS above 5%) and a high frequency of hair washing (e.g., every day).
Doesn’t Disturb Hair Integrity
These claims are also made for non-permanent hair dyes which simply use direct dyes to adhere to the hair. The hair shaft is not disturbed as the cuticle is not opened, therefore the claim can be made and easily substantiated, especially if cationic surfactants are present in the formulation.
