1,4-Dioxane: How I fell for a scare story


I got a question from iMarie.  “What are your thoughts about sulfates being contaminated with 1,4-dioxane? Thanks!” Well that brought back some memories.

It isn’t just skin care companies who use scare stories about dangerous chemicals to sell things.  The first scare story I have direct experience of was one done by a chemical supplier onto cosmetic chemists.   A lot of products used in cleansing products use materials that have been ethoxylated.  The ‘eth’ bit in names like sodium laureth sulfate comes from the ether group that has been added.  So sodium laureth sulfate is sodium lauryl sulfate that has been ethoxylated.  The term ‘ether sulfates’ describes a lot of shampoo ingredients all of which are sulfates that have been ethoxylated.  Ethoxylation is big chemistry carried out on a big scale with only a handful of ethoxylation plants on each continent.

1,4-Dioxane in Shampoo Ingredients

Now it happens that the process of ethoxylation produces traces of 1,4-dioxane as a byproduct.  Some time in the seventies somebody in one of the big chemical companies noticed that their plant happened to produce ether sulfates that had a lower level of 1,4-dioxane than their competitors.  They did some lab work and published a paper in the International Journal of Cosmetics pointing out that there were differences between the 1,4-dioxane levels in different suppliers of raw materials.  The reps then went round and pointed this fact out to the bench chemists formulating the products.  I was a young and enthusiastic but pretty green one myself at the time.

Well it made sense to me.  1,4-dioxane was a suspected carcinogen and one they were telling me that their stuff had less of it than the other guys.  Why would I be so irresponsible as to buy the less safe grade?

The competition soon caught up of course, and before long everyone was specifying the lower level of the impurity. The world was now a safer place.

Is 1,4-Dioxane Carcinogenic?

Or was it?  It never crossed my mind to look into 1,4-dioxane.  I just assumed it was a bad thing because people were going to the trouble over it.  It wasn’t for a couple of decades that I thought about it again when it started cropping up on lists of things that some natural product companies were against.  My first reaction was to think that at least this one was proper nasty, albeit one we had already sorted out.  But I had a look at the literature on it. To my surprise I found that this molecule was a lot more benign than I had ever realised.  It is not especially toxic nor particularly irritating.  What was the evidence that it was carcinogenic?

It turns out that three studies of people who work with it have revealed no ill effects.  It does have a dangerous feature. It has no smell and is very volatile so there have been some deaths of workers who have inadvertently been exposed to high levels in the atmosphere.

But the deaths were from very high doses, and anything can be dangerous if you have enough of it.  At low levels it is very hard to find any harmful effects at all.  The suspected carcinogenicity comes from a study in rodents which used levels many many times higher than you’d get in a shampoo.  There isn’t really a very good scientific way to assess whether a material is carcinogenic or not.  It isn’t ethical to deliberately expose humans to low levels of suspected carcinogens for a decade or so to see whether they have more cancer than you’d expect.  Monitoring people who happen to be exposed to it because of their jobs isn’t as good as a properly controlled study, but is often the best evidence you can get.  And on this score 1,4-dioxane is in the clear.

The survey is the most significant information, but we can’t ignore the animal data. However it is a lot weaker.  Using high levels of the material for short periods of times on a different species is not really a very good model for low level exposure over a long period.  There are any number of ways this test can give false positives or false negatives.  The weakness of this test is why it is described as a suspected carcinogen rather than an out and out one.

The third test is called an Ames test, which uses the biochemical behaviour of bacteria.  This again doesn’t have a perfect correlation with actual carcinogenicity.   As it happens this test shows 1,4-dioxane as a non-carcinogen.  But like the animal data it really isn’t strong evidence.

So What Is My Opinion of 1.4-Dioxane?

So the science is murky.  We can’t do the best test.  The second best test suggests things are okay.  The third best test highlights a potential problem.  The fourth best says it is fine.  On a balance of probability I have to say that 1,4-dioxane is very unlikely indeed to increase the risk of cancer at the level it occurs in finished products.  I know very well that the reaction to a statement like that might well be ‘well if the risk isn’t zero I don’t want to take the chance’.  To which my reply would be that a great many things we routinely use are just as likely to cause cancer as tiny traces of 1,4-dioxane.  A short trip in a car will expose you to a great many more chemicals with similar toxicological profiles than washing your hair will.

I have handled raw materials that have higher levels than those that the general public get exposed to, but speaking personally I sleep easily.  However risk is a weird thing and we all handle it in different ways.  If someone says that they can’t stand the thought of using a product that has the slightest link with cancer I have to respect that.  I am pretty inconsistent about my approach to health issues so I can’t really criticise.

But deliberately misrepresenting risk to sell things is a different matter entirely.  Which brings me back to the story I started with.  I do feel retrospectively a bit of a chump.  I was told some nonsense about the risk of dangerous chemical and bought it without checking.  Even if it does turn out that 1,4-dioxane is indeed a carcinogen it is very unlikely that the minute differences between the grades on offer would make any difference.  It would be perhaps the difference between smoking 20 a day and 19 a day.  But scare stories are easy to fall for.


I have the paper about 1,4-dioxane levels somewhere but I can’t lay hands on it at the moment.  If anyone knows the one I am talking about please let me know.

The EPA have done a very nice summary of the data on this chemical.


4 thoughts on “1,4-Dioxane: How I fell for a scare story

  1. Sam

    To me the bigger concern is its impact on the environment, specifically the waterways, something that Is controlled through the UK Pollution, Prevention and Control (PPC) Regulations and the UK Surface Waters (Dangerous Substances) Regulations (SI 1997/2560).
    Because it is considered so dangerous, especially to those that handle it, I believe production is highly restricted in the UK and the majority of production takes place overseas, where regulations are a little more lax…
    The question is, if we can manufacture solvents, surfactants etc via other means, why are we still using dioxane? and the answer is because it’s cheap and reaps higher profits!

  2. Colin Post author

    All good points Sam, but not relevant to cosmetics. The 1,4-Dioxane is there simply as a byproduct in parts per million. It isn’t produced as a raw material for use in cosmetics and nobody in the cosmetics industry handles the raw stuff. But you are quite right in principle. If there are unsafe chemicals in cosmetics it is much more of a problem for the workers making them and the environment. The consumers will get much lower doses.

  3. Sam

    It may well be there as a by-product, but if those products weren’t made, it would be by the by…
    Pun intended!

  4. Bereaved

    Colin’s Beauty Pages states “It isn’t ethical to deliberately expose humans to low levels of suspected carcinogens for a decade or so to see whether they have more cancer than you’d expect”

    What, one wonders, is the difference ETHICALLY between that and exposing millions of unsuspecting CUSTOMERS for a decade or so to a product containing low levels of a suspected carcinogen and not even bother to see whether they have more cancer than you’d suspect??

    Perhaps those who OWN companies whose manufacturing processes produce the chemical in their products would be perfectly willing to participate in such a scientific experiment/survey after all they are happy to SELL such products to others and they would all ready have all the scientific facts regarding the “safety” of this suspected carcinogen.

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