Feeling it’s time to freshen up your hair colour? Many people who use hair dye do so without any evident problems. Unfortunately, that’s not the case for everyone.

Exact figures are hard to find but estimates suggest more than 70 percent of women and 20 percent of men colour their hair. And we’re starting younger and doing it more often.

Even if you’ve used hair dye many times with no adverse effects, it’s possible you could become sensitised to an ingredient and have a reaction the next time you colour your hair.

The culprit? Hair dyes typically contain ingredients known as “strong” or “extreme” skin sensitisers – substances that can potentially cause severe allergic reactions.

Common ingredients

One of the most common sensitisers is called p-phenylenediamine (PPD). PPD is classified as an extreme sensitiser and is identified as a key cause of allergic reactions to hair dye.

It’s estimated PPD is used in more than two-thirds of permanent hair dyes you can buy off the shelves, including products marketed as “natural”, and is also common in salon dyes.

Regulations here allow PPD to comprise up to 2 percent of a hair dye.

Manufacturers aren’t required to state exactly how much PPD is present and, depending on the colour, the level can vary. There tends to be more PPD in darker dyes, bad news for wannabe brunettes. Semi-permanent dyes, which use different ingredients, don’t usually contain PPD.

Adverse reactions

Dermatologist Dr Amanda Oakley says allergic reactions range in severity. They occur when the body thinks a chemical is harmful and produces an immune response against it. The result is usually an acute contact dermatitis affecting all areas touched by the dye especially the face, neck and scalp.

Some allergic reactions may not happen straightaway. Dr Oakley says reactions to PPD, for example, usually occur between 6 and 36 hours after use. Symptoms can include marked reddening, swelling and blistering. The reaction tends to be less severe on the scalp than on the more sensitive skin of the face and neck.

In rare cases, allergy to a hair dye ingredient can cause anaphylaxis. This is an extreme allergic reaction that can be life threatening if not treated quickly. Symptoms include an immediate itchy rash, wheezing, difficulty breathing, faintness and collapse.

Hair dyes containing PPD and other sensitisers must carry the following warnings:

  • Hair colourants can cause severe allergic reactions.
  • Do not colour your hair if:
    • you have a rash on your face or a sensitive, irritated or damaged scalp
    • you have ever experienced any reaction after colouring your hair
    • you have experienced a reaction to a temporary "black henna" tattoo in the past.
  • This product is not intended for use on persons under the age of 16.
  • Temporary "black henna" tattoos may increase your risk of allergy.

Problems with patch tests

To test whether you’re allergic to a product, dye manufacturers usually recommend a patch test 48 hours before use. This involves applying a small amount of the product to your forearm or behind your ear. If a reaction occurs, you shouldn’t use the dye.

But patch tests may not be 100 percent reliable. The EU’s Scientific Committee on Consumer Products has previously cautioned there’s a risk patch tests can give misleading and false-negative results.

The committee found patch tests can give people the false impression they’re not allergic or not at risk of developing an allergic reaction. One reason for this is the reaction time – reactions can take up to 7 days to develop, not just 48 hours.

We say

  • Further research is needed to assess the safety of ingredients used in hair dyes and their long-term effects.
  • There are no widely accepted alternatives to the chemicals used in hair dyes. Almost all permanent hair dyes – used either at home or at the hairdressers – are likely to contain extreme or strong sensitisers.
  • If you do experience an allergic reaction, see your doctor for treatment. And don’t use the product again.