Anyone can develop an allergy to anything anytime. Allergic reactions vary in severity, but in rare cases some can kill you. So when you make it to your bed tonight you can thank providence for sparing you for one more day.

But lets get things in perspective. Although in theory anything can be an allergen in practice if you want a successful career as an allergen you really need to be able to get into the bloodstream reasonably easily. The immune system also has to interpret it as a problem. So very common things, like sugar for example are not going to provoke allergies. Nor are things that just don’t react very much. So you can use things like silicone in breast implants with few problems.

To provoke an allergic reaction the immune system needs to have contact with the allergen first, so it can recognise it and produce a reaction to it. This means that the soonest you can develop an allergic reaction is the second time you come into contact with it. More often you’ll need to have had a fair bit of exposure first.

Allergies are a fact of life and are on the rise. The reason for the increase isn’t immediately obvious, but I think a biochemist I heard on the radio isn’t far off. She says that basically the way we live now doesn’t leave much for the immune system to do. So when it does find something to react to, it does it in a big way. The most extreme of reactions is anaphylaxis. The so called anaphylactic shock is so severe that it can be life threatening or even fatal. Luckily this kind of reaction is extremely rare, leading to only about 20 deaths a year in the UK, but even so it is a sobering thought that there might be no particular indicator that someone is prone to one until they have one.

As a rule cosmetic products don’t cause this kind of problem because they don’t contain much that will get through the skin into the bloodstream, and because very few cosmetic ingredients have much potential to provoke allergic reactions. But if you were going to pick on the products that have the strongest chance, hair dyes are the ones that are most likely to be an issue. For a start, the colourants have to get into the hair to have an effect, and this means that they are likely to get across the skin and into the blood stream if they get the chance as well. On top of that they tend to be used with things like ammonia which are likely to irritate the skin and make it more permeable. (These are the culprits if your scalp feels dry and itchy after you have dyed your hair).

Most of the colourants used are at least potentially likely to provoke an allergic reaction. One in particular, p-Phenylenediamine, has been shown to cause allergies in quite a large proportion of people. I haven’t been able to find any figures for the population as a whole, but a recent study in Thailand found just under 7% of people with eczema reacted to it. People with eczema are way more likely than anyone else to be sensitive to chemicals in general because they have both weaker skin barriers and very active immune responses. So if only 7% of them react to it the number of reactions in the population as a whole is going to be pretty low. On top of that the amount getting into the blood stream during the hair dying process is not going to be very high. Applied with care the likelihood is it will be close to zero. So the risks of getting any kind of reaction at all is pretty slim.

But even so, lots of hair dyes get sold and even a very low level of reaction means that there are a great many reactions to them reported. Of course a skin reaction is a long way from being a fatality. Millions of hair dyes are sold every year, so this is just as well. There are only about 20 deaths every year from anaphylaxis. How many of those deaths can be attributed to the use of hair dyes? The answer is nobody knows, but the probability is that it is none of them. Drug reactions, foods like peanuts and bee stings are all listed as major causes of anaphylactic shock. Neither of the cases in the news at the moment have definitively been linked to any chemical in hair dye, let alone the specifically the p-Phenylenediamine which is being discussed in some of the press coverage.

So on the whole, I don’t think there is a great risk of suffering any ill effect from using a hair dye. I don’t use them myself as a matter of course, but as it happens I am just starting on a project where I will be using exactly the p-Phenylenediamine that some journalists are raising concerns about. Having looked into it, I am quite happy to carry on and don’t feel in the slightest danger. But I have to concede that there is a risk, albeit in the hundred millions to one against. If however you don’t want to take any risk at all there is one and only one course of action open to you. That is to stop dying your hair all together. Simply avoiding hair dyes that contain p-Phenylenediamine is not enough. The way the immune system works, you cannot be sure that you won’t get the same reaction from closely related chemical species. So the other components of hair dye are quite likely to have the same effect. Switching to natural alternatives won’t help. These have pretty much the same problem. The lawsone found in henna has enough similarities to p-Phenylenediamine that there is still a risk that it would provoke the same reaction.

Your attitude to risk is a personal matter and none of us are very good at being entirely logical about it. We all know about the risks of illicit drugs, casual sex, smoking and alcohol, or even driving our cars too fast, but we all do at least some of these things (though probably not al at the same time). On the whole, the chances of coming to any harm from a hair dye, which is microscopic compared to risks we routinely take every day seems to me to be not worth worrying about. You may disagree, and you are perfectly entitled to do so. But please don’t get suckered into buying special ‘safe’ brands that avoid particular ingredients. PPD Free brands for example won’t be any safer.


I was surprised to see an article in the Guardian – the home of statistics superhero Ben Goldacre – pushing this story. It has to be said that the author is rather cavalier with her own health. She seems to have had an anaphylactic episode, which according to this account was life threatening, but has not followed this experience up with a patch test to positively identify the causative agent or agents. The whole tone of the article is a bit alarming. This is only achieved by glossing over the fact that there is no proven link between p-Phenylenediamine and either of the two cases quoted.

This is the paper that assessed the degree of reactions to some common allergens among eczema patients. It was done in Thailand where the pattern of exposure to hair dye ingredients might be very different to that in other countries, but nonetheless it gives an idea.

J Med Assoc Thai. 2010 Dec;93 Suppl 7:S7-14. Contact allergy in eczema patients in Thammasat University Hospital. Disphanurat W.


From the UK, Colin Sanders has been a formulator of cosmetic and topical pharmaceuticals for 27 years. Over that time he has formulated nearly every category of product including shampoos, cosmetic skin creams, pharmaceutical skin creams, face masks, lip balms and so on. Colin has been an active member of the Society of Cosmetic Scientists since 1985, and in 1999, organized the first of the Formulate shows. His degree is in environmental science, and he continues to take a keen interest in the impact of human activities on the planet. Colin regards himself as an environmental activist and all round green. When not in the lab, he writes a blog, Colin’s Beauty Pages, with the intention of entertaining and hopefully informing users of cosmetic and personal care products with some insider insights, a bit of science and his own opinions.

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