Myth: SLS causes cancer

So I entitled this one myth (as opposed to the unbiased myth or fact) because it is fictitious and a very popular urban legend. I think the story was spun by manufacturers trying to sell the benefits of not using sulfate but there is simply no fact to this story.

I can only emphasize the need to use scientific sources (meaning articles in journals that you can countercheck and scientific bodies that are trusted.)

For example, a popular justification is to link SLS to nitrosamines, yet ironically the production of SLS does not involve any nitrogen. Additionally sometimes it is purpoted that SLS can react with formaldehyde to produce nitrosamines, again no nitrogen in SLS or formaldehyde. Nitrogen is the key element in amines, so if there is no nitrogen, where do nitrosamines come from? This is pure science fiction.

The second part of the cancer myth involves 1,4 dioxane which is a by product of a complimentary process known as ethoxylation. Ethoxylation is usually performed to reduce the irritancy of SLS and separately to produce humectants such as polyethylene glycol (PEG).

According to the FDA 1,4 dioxane evaporates readily which greatly reduces its ability to penetrate into the body. Also  a process known as vacuum stripping is an industry standard recommendation (meaning the dioxane is allowed to evaporate before the product is used)

1. FDA currently does not have a specific limit on dioxane and has not determined it to be a hazard
2. American Cancer Society clearly states that SLS is not a known carcinogen (i.e it is not currently known to cancer)

As with all good science, we can only state facts as we understand them currently, if SLS is ever revised to be a carcinogen, you will read about it here!

Finally, here is the full reading list on SLS
1. Myth or Fact: SLS breaks Hair (part 1 of 2)
2. Myth or Fact: SLS breaks Hair (part 2 of 2)
3. Myth or Fact : SLS is an irritant


  1. Hi, thanks for your informative post.

    I have a question pertaining to coloring hair, and I'm hoping you will be able to help me out.
    I'm a new natural with super coily/curly 4a/b hair.
    Some background:
    I did the big chop, so i only have 1 inch of hair. Before that my hair had been relaxed for ages, so I had no idea what my texture truly was. The day I big chopped, I put in a color.

    Today someone insinuated that i have the texture i do because of the color. Is it possible for color to make hair curlier/more defined??


  2. Some colour treatments can change hair texture because of the inclusion of ingredients that affect hair protein structure (for example a pretreatment with alkali to allow the colour to penetrate).

    However in practice, most times hair colour simply just colours the hair. It is most likely that your hair texture simply is the curly variety!

    I would say don't pay too much attention to other people's comments (It seems to me that the person was having an attack of the green eyed monster). In a few months when you have more hair, you will be able to assess your hair texture better. For the moment just enjoy your new cut and colour!

  3. Thank you, and love love love your blog!

  4. Who in the world thought SLS caused cancer! Thats the first time I've ever heard that. SLS is strips your hair and skin of a lot of oil causing dryness. People really need to take the time to research things people are telling them. There are a lot of people out here in the blogging world giving info that is enough truth to be passable but enough lie to be damnable. Thanks for giving people good information


  5. In passing I read something about sls or parabens being found in breast cancer tumors. It was years ago - more than 3 I think. I'm leery of both, but since I don't leave it in my hair for more than a few minutes at a time, I figure I'm safe.

  6. DEA,surfactant stabilizer found in everyday foaming cleansers proven to kill brain cells and slow cellular growth. (Niculescu et al.2007)

    1,4 Dioxane found in soaps bc as a toxic contaminant of (sls/sles). It is readily absorbed through the lungs,skin,gi track. found to cause cancer in lab rats and tumors(Stickney et all, 2003)

    SLS/SLES:skin and eye irritant usually contaminated with the two ingredients above as well as other carcinogenic contaminates. Most products that test pos for 1.4 dioxane are foaming cleansers with sls and sles or both.

    FDA employs a hands off approach to beauty products. there is no harm until harm is proven. the FDA regulates products only after they are sold, investigating health complaints when and if complaints are filed. The Dept /Ag does not require 1.4 dioxane to be listed as an ingredient on product labels.There is not enough info on alternatives to animal testing to validate the use of chertain chemicals, so the FDA will only accept animal safety data.When complaints are filed with the FDA it takes decades to gain enough complaints to invoke an investigation. Then another decade to convince legislatures that they should ban a substance. It took the FDA 20 yrs to ban the use of lead in paint on toys and furniture. The European Union has banned most of the lethal ingredients the FDA allows until the research is done otherwise; and, the companies are not interested in proving that their ingredients are faulty.

    So, no, alone SLES/SLS is only a stripping surfactant that irritates. To bring the substance to market, and the tests related to composition of SLS/SLES prove that it is full of carcinogens.

    So you make the call.

  7. The Knotty Truth, nice to see some references (it would help though if you cited a journal and page number to make it easier to find).

    I have actually already covered the info in this post but just to anyone else reading your comment I would like to say

    1. 1,4 dioxane as stated in this post is NOT found in SLS. It is a biproduct of ethoxylation of SLS. It can be found in SLES products but it would not be normal to find it in SLS.

    2. 1,4 dioxane evaporates when exposed to air giving it a significantly reduced chance of entering the skin. SLES is routinely processed in this way (i.e air pumped continuously over the batch)

    The European Union (of which UK is a part of and where I live) has not banned SLS or SLES. There are hundreds of shampoos which contains SLES and SLS.

    I am not sure how familiar you are with animal testing, the truth is there is no single animal that could accurately predict what will happen in a human being. On a serious note, there are plenty of drugs which undergo rigorous testing in animals to check if they cause death or injury but even if they do pass, there is the real and serious risk that the drug could still be harmful to humans. I therefore take any test done on an animal with a massive pinch of salt.

    Most cosmetic companies actually employ human beings to test their products and as a result have to be extremely cautious that their product will not cause death or injury.

    It is fair enough to be critical of the FDA but seriously do think about this, do you really think that P&G, L'Oreal etc would risk the lawsuits if they were selling millions of bottles of carcinogens? What would be the reason to risk financial ruin?

  8. I have seen many comments on the internet saying that SLS can create hormone problems "mimic the activity of the hormone Oestrogen" Although no references are given to research. Do you know of any research to confirm this theory?

    Also, the 1,4 dioxane in SLES does worry me. Would 1,4 dioxane be listed on the ingredients of products containing it? or will it always be present at some level in products with SLES?

  9. Anon sorry your comment was marked as spam so I only just approved it. SLS is not a hormone mimic, parabens are slight hormone mimics but nothing like the contraceptive pill.

    Dioxane would not be listed because it is usually a trace amount (i.e well under 0.1%) for properly formulated products. It is unlikely that a product with SLES will be completely free of 1,4 dioxane


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