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All about hair colouring

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A hairdresser colours a client's hair

Hair colouring is the practice of changing the colour of hair. The main reasons for this practice are cosmetic (e.g., to cover gray hair, to change to a colour regarded as more fashionable or desirable, or to restore the original hair colour after it has been discoloured by hairdressing processes or sun bleaching). Hair dyeing, which is an ancient art, involves treatment of the hair with various chemical compounds. Today, hair colouring is immensely popular, with over 75 percent of American women dyeing their hair, and globally hair colourants are a rapidly growing over-$7 billion industry. At home colouring in the United States reached $1.9 billion in the year 2011, and is expected to raise to $2.2 billion by 2016.


Portrait of Lafayette in 1830, aged 73, with pitch-black hair.

The dyeing of hair is an ancient art. In ancient times, the dyes were obtained from plants. Some of the most well known are henna (Lawsonia inermis), indigo, Cassia obovata, senna, turmeric and amla. Others include katam, black walnut hulls, red ochre and leeks. In the 1661 book Eighteen Books of the Secrets of Art & Nature, various methods of colouring hair black, gold, green, red, yellow, and white are explained. The development of synthetic dyes for hair is traced to the 1860s discovery of the reactivity of para- phenylenediamine (PPD) with air. Eugène Schueller, the founder of L'Oréal, is recognized for creating the first synthetic hair dye in 1907. In 1947 the German cosmetics firm Schwarzkopf launched the first home colour product, "Poly Colour".  Hair dyeing is now a multibillion dollar industry that involves the use of both plant-derived and synthetic dyes.


Hair colour was traditionally applied to the hair as one overall colour. The modern trend is to use several colours to produce streaks or gradations, not all work on top of a single base colour. These are referred to as:

  • Highlighting, where sections of hair are treated with lighteners, and they usually create blonde streaks.
  • Lowlighting, where sections of hair are treated with darker hair colour.
  • There are also newer application techniques such as ombré, in which hair is dark on the crown and bit by bit becomes lighter toward the ends, and splashlights, in which a horizontal band of bleached hair stretches from ear to ear.

These are off-the-scalp techniques, and can be applied by the following methods:

  • Foiling, where pieces of foil or plastic film are used to separate off the hair to be coloured; especially when applying more than one colour. This keeps the colour only on the desired pieces of hair and protects the rest of the hair.
  • Cap, when a plastic cap is placed tight on the head and strands are pulled through with a hook. This method is not frequently practiced anymore with the exception of short hair highlighting.
  • Balayage, where hair colour is painted directly onto sections of the hair with no foils used to keep the colour contained. This method is growing in popularity because of its ability to look more natural and less placed.
  • Dipping or tip dyeing, similar to balayage in that the colour is painted directly on the hair, this focuses on a more solid level of coverage on the ends of the hair.

All application techniques can be used with any type of colour. For lightening, the hair will sometimes have to be bleached before colouring.

Hair colouring can also be applied on the scalp for a more solid level of coverage

  • Root Touch-Up, where colour is applied only to the most recent section of re-growth. Usually the first inch of hair from the scalp. Generally those getting root touch-ups get this service repeated every 4–6 weeks as the natural colour grows in and becomes apparent.
  • All-Over Colour, where the individual desires for all of their hair to be a different solid colour.
  • Block Colouring, where the individual wants 100% coverage but desires two or more colours to be placed resulting in dimension and contrast.

All application techniques can be used with any type of colour. For lightening, the hair will sometimes have to be bleached before colouring.

Hair with blonde highlights


The four most common classifications are permanent, demi-permanent (sometimes called deposit only), semi-permanent, and temporary.

A very popular way to achieve permanent hair colouring is through the use of oxidation dyes (see below).

Demi-permanent hair colour is hair colour that contains an alkaline agent other than ammonia (e.g. ethanolamine, sodium carbonate) and, while always employed with a developer, the concentration of hydrogen peroxide in that developer may be lower than used with a permanent hair colour. Since the alkaline agents employed in demi-permanent colours are less effective in removing the natural pigment of hair than ammonia these products provide no lightening of hair's colour during dyeing. As the result, they cannot colour hair to a lighter shade than it was before dyeing and are less damaging to hair than their permanent counterpart.

Demi-permanents are much more effective at covering gray hair than semi-permanents, but less so than permanents.

Demi-permanents have several advantages as compared with permanent colour. Because there is essentially no lifting (i.e., removal) of natural hair colour, the final colour is less uniform/homogeneous than a permanent and therefore more natural looking; they are gentler on hair and therefore safer, especially for damaged hair; and they wash out over time (typically 20 to 28 shampoos), so root regrowth is less noticeable and if a change of colour is desired, it is easier to achieve. Demi-permanent hair colours are not permanent but the darker shades in particular may persist longer than indicated on the packet.

Semi-permanent hair colour has smaller molecules than temporary dyes. These dyes only partially penetrate the hair shaft. For this reason, the colour will survive repeated washing, typically 4–5 shampoos or a few weeks. Semi-permanents contain no, or very low levels of developer, peroxide or ammonia, and are therefore safer for damaged or fragile hair. However, semi-permanents may still contain the possibly carcinogenic compound p-phenylenediamine or other such ingredients. The U.S. Environmental Protection Agency reported that in rats and mice chronically exposed to PPD in their diet, it simply depressed body weights, and no other clinical signs of toxicity were observed in several studies.

The final colour of each strand of hair will depend on its original colour and porosity, so there will be subtle variations in shade across the whole head. This gives a more natural result than the solid, all over colour of a permanent colour. However, it also means that gray or white hairs will not appear as the same shade as the rest of the hair. If there are only a few grey/white hairs, the effect will usually be enough for them to blend in, but as the gray spreads, there will come a point where it will not be disguised as well. In this case, the move to permanent colour can sometimes be delayed by using the semi-permanent as a base and adding highlights.

Semi-permanent colour cannot lighten the hair.

Temporary colour
Temporary hair colour is available in various forms including rinses, shampoos, gels, sprays, and foams. Temporary hair colour is typically brighter and more vibrant than semi-permanent and permanent hair colour. It is most often used to colour hair for special occasions such as costume parties and Halloween.

The pigment molecules in temporary hair colour are large and cannot penetrate the cuticle layer. The colour particles remain adsorbed (closely adherent) to the hair shaft and are easily removed with a single shampooing. Temporary hair colour can persist on hair that is excessively dry or damaged in a way that allows for migration of the pigment to the interior of the hair shaft.

Alternative colour
Alternative hair colouring products are designed to create hair colours not typically found in nature. The available colours are diverse. For example, the colours green and fuchsia.

Permanent alternatives in some colours are available from big hair care brands. Some alternative colour shades are blacklight-reactive, to show up under nightclub lighting.

The chemical formulae of alternative colour dyes typically contain only tint and have no developer. This means that they will only create the bright colour of the packet if they are applied to light blond hair. People with darker hair (medium brown to black) need to use a bleaching kit before tint application. Some people with fair hair may benefit from prior bleaching as well. Gold, yellow and orange undertones in hair that has not been lightened enough can adversely affect results, especially with pinks, blues and greens. Although some alternative colours are semi-permanent, such as blue and purple, it could take several months to fully wash the colour from bleached or pre-lightened hair.

Hair and beard coloured blue


Hair colouring involves the use of chemicals capable of removing, replacing and/or covering up pigments naturally found inside the hair shaft. Use of these chemicals can result in a range of adverse effects, including temporary skin irritation and allergy, hair breakage, skin discolouration and unexpected hair colour results.

Skin irritation and allergy
In certain individuals, the use of hair colouring can result in allergic reactions and/or skin irritation. Symptoms of these reactions can include redness, sores, itching, burning sensation and discomfort. Symptoms will sometimes not be apparent immediately following the application and processing of the tint, but can also arise after hours or even a day later.

To help prevent or limit allergic reactions, the majority of hair colour products recommend that the client conduct a patch test before using the product. This involves mixing a small quantity of tint preparation and applying it directly to the skin for a period of 48 hours. If irritation develops, manufacturers recommend that the client not use the product.

European dermatologists have, however, strongly advised against such pre-use testing, as it entails additional sensitisation (allergy) risk and the interpretation by lay people may not be sufficiently accurate.

Hair breakage
Hair that has been damaged by excessive exposure to chemicals is considered over-processed. This results in dry, rough and fragile hair. In extreme cases, the hair can be so damaged that it breaks off entirely. This is especially true for Afro-Caribbean hair, especially if used in combination with relaxers. Treatments are available but the only real solution is to stop the use of chemicals until new hair grows and the damaged hair is cut off.

Skin discolouration
Skin and fingernails are made of the similar type of keratinized protein as hair. That means that drips, slips and extra hair tint around the hairline can result in patches of discoloured skin. This is more common with darker hair colours and persons with dry absorbent skin.

This discolouration will disappear as the skin naturally renews itself and the top layer of skin is removed (typically takes a few days or at most a week). A good way to prevent dye discolouration is to put a thin layer of petroleum jelly or any oil-based preparation around the hairline. It is recommended that latex or nitrile gloves be worn to protect the hand.

Unintended results
Several factors influence the final colour of the hair following the colouring process.

  • For semi-permanent and demi-permanent colour, the final colour is a blend of the natural colour of the hair and the dye colour.
  • Bleached hair will often require pre-pigmentation before a colour application. Dyeing bleached hair brown can result in grey or very ashy (grey sheen) hair.
  • Previously colour treated hair can react unpredictably with subsequent colour treatments.
  • Previous use of shampoos which deposit a layer of plastic on the hair can block the action of the dye.
  • Presence of minerals, salts, chlorine or other contaminants in the water used in the colouring process
  • Certain prescription drugs can alter hair chemistry
  • Colouring dark hair to achieve a desirable shade of blond requires bleaching, followed by a secondary colour treatment. Bleached hair can still have a yellow or coppery shade. A violet-based colour can cancel out yellow tones, and a blue-based shade will cancel out coppery orange.
  • Porosity of hair can affect the final shade. Porous hair often absorbs more colour, which sometimes makes darker than expected.

Health concerns

  • The salt lead acetate (the active ingredient in gradual darkening products such as Grecian formula) is toxic. Lead acetate trihydrate has also been shown to cause reproductive toxicity.
  • Articles link the development of some forms of cancer (including leukemia, non-Hodgkin's lymphoma, bladder cancer, blood cancer, and multiple myeloma) with use of hair colour. More specifically, prolonged use of permanent dark hair dyes can double a person's risk of getting some types of blood cancer.
  • In 2004 a known human carcinogen, 4-aminobiphenyl or 4-ABP, was found in some commercial hair dyes. However, evidence is limited and inconsistent for the link between cancer from hair dye.
  • Phenylenediamine is known to cause health concerns, such as skin irritation. Exposure to phenylenediamine can occur during manufacturing or during the use of hair dyes. According to the Product Safety Summary Sheet by DuPont, Para-Phenyenediamine (PPD) is labeled as toxic and can cause adverse effects on aquatic organisms and could cause long-term effects in aquatic environments.


Henna is an orange dye commonly used as a deposit-only hair colour whose active component, lawsone, binds to keratin. It is therefore considered semi-permanent to permanent, depending on a person's hair type. Most people will achieve a permanent colour from henna, especially after the second dye. With repeated use the orange colour builds up into red and then auburn. While "natural" henna is generally a red colour, variations exist. These variations usually contain ingredients from other plants and even synthetic dyes.

Indigo is natural dye from a plant (Indigofera tinctoria, suffructicosa, or arrecta) that can be added to henna or layered on top of it to create brown to black colours in the hair. On the colour wheel, henna is orange, and indigo is blue, so as complementaries, the two colours work together to create brown tones. Like henna, indigo may fade after one application, but it becomes permanent on the hair with repeated use.

Using a plant-based colour such as henna can cause problems later when trying to do a perm or permanent hair colour. Some store-bought henna contains metallic salts which reacts to hydrogen peroxide that is used in hair lightening. This may lead to unpredictable results, such as green or blue tones in the hair. Henna is a healthy way to colour hair, as long as no metallic salts are used.


Hair dyes are cosmetics in contact with the skin, containing chemical products which can be dangerous for health. This is why these products are highly regulated, and some substances which have been scientifically proven hazardous, in general or from a certain concentration or quantity are being officially and legally forbidden or restricted.

The European Union is particularly stringent when it comes to health regulations. In an effort to ensure that hair dyes contain only safe substances, the European Commission adopted the Directive 2012/21/EU to restrict the use of around 45 chemicals in hair dyes. The directive on dyes is part of a general and comprehensive set of regulations, the EU Cosmetics Directive 76/768/EC.

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