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Chemicals and Hair Colourants

By: Helena Stratford - Updated: 20 Nov 2010 | comments*Discuss
Chemicals Hair Hair Dye Dye Colouring

Whether we want to look younger, change our image, or improve on what Nature gave us, we’re big fans of hair colour – in fact 70% of us have a go, with most re-applying colour 6-8 times annually. Last year alone we bought 56 million colouring kits and had another 60 million applied professionally.

But is it safe?

What Do Hair Colorants Do?

This might seem a silly question, but it’s one pertinent to the debate of whether hair dyes are safe to use. If we understand the way in which colorants work, we can then choose how exposed we are to the chemicals they contain.

The two main ways of colouring hair are either to used organic, natural dyes, which can give more variable results but contain less or no manufactured chemicals, or industrial, chemical dyes which give more predictable and longer-lasting results.

Methods Of Colouring

There are then three main ways to colour the hair, all of which will dull or damage the hair to some degree.

  • Tinting
  • Applying semi-permanent colours
  • Applying permanent Dyes

Tinting is the least damaging method used, as it merely coats the hair with colour without penetrating the actual shaft.

Semi-permanent colours are designed to last less long than permanent dyes and will gradually wash out or fade over a matter of weeks. Nevertheless they do contain ammonia which is harsh on the skin and hair, plus the chemicals resorcinol and phenyledamines which can cause irritation.

Permanent colours, which 80% of people opt for, are the most damaging of all. The colour is designed to penetrate the hair shaft, changing the structure and ‘locking’ in the dye with bleaching agents stripping the hair of its natural pigment and allowing the dye to be absorbed.

Health Risks And Chemicals

All dyes carry a health risk – even natural dyes such as henna can cause an allergic reaction, so it is imperative that a patch test be done before attempting to apply any kind of colour to hair.

Even so, tests can be misleading and the chemicals in hair dyes can cause itching, inflammation, and in the most severe (and rare) cases trigger contact dermatitis and even anaphylactic shock.

The chemicals toluene 2.5-diamine and para-phenylenediamine (PPD) in hair dye have been singled out as being the most common allergens in hair dye.


Hair dye uses an ingredient called toluene-2.5-Diamine (TDA). It is closely related to another toluene which has already been banned as a potential carcinogen and there are now concerns about TDA which is also highly toxic.


Two thirds of all hair colours contain p-phenylenediamine or ‘PPD’. The darker the hair dye, the more PPD is found in the product and the greater toxicity it has. It is highly allergenic and has also been linked to a possible increase in some types of cancer.

Aromatic Amines

This controversial group of chemicals include amonoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA). They are generally used as preservatives, foaming agents, as PH adjusters and as emulsifiers. However they can cause irritation, contact dermatitis, and have been associated with endocrine disruption and cancer.

Hair Colorants And Cancer

Whether there is a causal link between using hair dye and developing cancer has been the subject of a number of studies. Although nothing has yet been substantiated, it has been found that regular use of hair dye – and especially for people using them prior to the 1980’s when dyes were more toxic, and those who work with dyes in salons – could be at greater risk.

One study showed that hairdressers who had worked for a decade or more with hair dyes, were ill five times more often than those who hadn’t and suffered a greater risk of cancer of the bladder and that women who dyed their hair once a month or more, were also twice as likely to develop this form of cancer than those who didn’t use hair colour at all. However, it’s important to reiterate that more research needs to be done and that other factors should be taken into account.

Another form of cancer linked to the use of hair colour is that of chronic lymphocytic leukaemia, a form of blood cancer. One study claims that using a hair dying product more than nine times per year could increase the risk of this type of cancer by up to 60%.

If dark coloured dyes such as reds, browns, and blacks are used, which contain more chemicals to be effective, then there could be a 50% increase in the risk of developing a form cancer called follicular lymphoma.


Currently there is little regulation controlling the chemicals found in hair dye. However, because of the research indicating potential risks, the EU recently banned 22 chemicals which didn’t satisfy safety standards.

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