Be safe and always do the allergy alert test

Last year an estimated 50 million packs of home hair dye were sold in the UK alone. Did you buy one? If so – be honest – when you read the instructions that said, “It is essential that you perform an allergy alert test 48 hours before each use of this product”, did you follow the advice to the letter? Or just go right on and use the product, reassuring yourself that you’ve been using the same colour for years and never had a problem?

Like many of us, you probably skipped the test and got colouring. But these alert tests aren’t optional, they’re essential. To understand why, you have to understand a little bit about the chemistry of colouring hair and the nature of allergy.


“To colour hair permanently, molecules of colour need to be captured within the hair shaft,” explains Dr Emma Meredith, director of science at the Cosmetic, Toiletry & Perfumery Association (CTPA). “The problem is that the molecules of colour are too large to penetrate the shaft, so you have to make them inside the hair shaft.”

This is done by applying two components, one that contains substances called colour precursors and another, known as an oxidising agent, which is usually hydrogen peroxide. These are both small enough to get into the hair. Once inside, they react with each other to create the colour molecules which are then trapped in there, resulting in the hair being permanently coloured.

One of these smaller colour precursor molecules is a substance called PPD (paraphenylenediamine or p-phenylenediamine) and, while for most people PPD won’t cause any problems, there are a small number of people who may have an allergic reaction to it, in the same way that some people may be allergic to peanuts or shellfish.

Reactions can be avoided by carrying out an allergy alert test 48 hours before using a hair colourant and every time you dye your hair

“An allergic reaction happens when the body’s immune system reacts to a substance that is normally harmless,” explains Dr Chris Flower, director-general of the CTPA, and a chartered biologist and toxicologist. “Your potential to be allergic to something is determined by your genes and you won’t get an allergic reaction the first time you encounter something as your immune system has to have met the allergen in the past, and decided it is harmful to you, before it can react.”

Instead allergies build up over time and after a number of exposures to an allergen, a threshold will be reached which will result in an allergic reaction. It’s like a glass of water; once full, adding more will make the glass overflow.

“Less than 1.5 per cent of the population have the potential to react to PPD and around 0.1 per cent of the population will develop an allergy after hair colourant use,” says Dr Meredith. “When you compare that with food allergies, which can affect up to 5 per cent of the population, that’s actually quite low. Although for those who do become allergic, it is a serious matter.”

And, she stresses, reactions on the head and face can be avoided by carrying out an allergy alert test 48 hours before using a hair colorant and every time you dye your hair. Below is a detailed guide to doing the test.

But it’s not just about going through the motions. “You have to pay attention to how you’ve reacted to dyes or tests in the past. If there was even the slightest bit of redness or itchiness, this is a sign you shouldn’t be using that product – and probably any permanent hair colourant. It’s also important, if you do react to the allergy alert test, that you speak to your doctor and also contact the manufacturer – careline or helpline numbers are provided on the pack.”

So if you are one of the very small number of people who can’t use products containing PPD or you’re desperate to colour your hair before you go out tonight, what’s the solution?

“Look for a product that doesn’t require an allergy alert test,” recommends Dr Meredith. “Temporary hair colours, such as mousses, mascaras and chalks are less likely to contain PPD or a PPD-like dye and can usually be used straight away.”

But when it comes to allergic reactions to PPD, the biggest danger is not hair colourants which, when used according to the instructions are perfectly safe, but temporary, so-called “black henna” tattoos, often offered at funfairs, festivals and in holiday resorts.

According to the British Skin Foundation, the majority of the colourant in black henna is PPD – legally allowed to be present in limited concentrations in hair dyes, but illegal for use on skin in these types of tattoos within the European Union.

“Having a ‘black henna’ temporary tattoo presents a significant risk of a very nasty adverse reaction to the tattoo itself,” says Dr Flower.

Indeed, in a survey, 40 per cent of dermatologists asked said they had treated patients for reactions to these tattoos. But crucially, if you do have the potential to be allergic to PPD, it can give you a high exposure to the allergen, topping up your “water glass” with huge implications for the future.

“If you have one of these tattoos, even in childhood, it increases the risk of you either not being able to use most hair dyes in the future or having a bad reaction to them if the warnings are ignored,” Dr Flower says.

The message is clear – never have a “black henna” temporary tattoo and always do the allergy alert test.


Dr Anjali Mahto, consultant dermatologist and British Skin Foundation spokeswoman, says: “Black henna is well known to cause skin reactions and should be treated with caution, particularly in children. Individuals presenting to dermatology outpatients with a history suggestive of contact allergy to hair dye should also be questioned closely regarding previous reactions to black henna. In most cases, patients with a reaction to PPD, who present to outpatients, are usually rash free and the reaction has occurred at some point in the past. In these cases, patient photographs can be extremely helpful. When patients acutely present, usually as an emergency appointment, a range of skin changes can be visible. These include redness, itching, blistering and swelling. Long term, there may be residual pigmentation changes in the skin at the site of PPD application.”