Why you should avoid SLS and SLES
Recently products have started to appear that make the claim of being SLS or sometimes SLES free. What are they and why should you be interested?
SLS stands for sodium lauryl sulphate and SLES stands for sodium laureth sulphate. They are very similar molecules, and for all intents and purposes you can regard SLES as a mild form of SLS. SLES is made from SLS and it is very difficult to obtain SLES that doesn’t contain some SLS. For the rest of this article I will only talk about SLS, but everything I say will apply equally to SLES.
Both these materials are present in the vast majority of hair shampoos and foam baths that you can buy on the market at the moment. In fact, in 2000 when some German researchers wanted to investigate this material they found that 97% of their prospective subjects already had it on their skin.
The reason it is popular is that it is pretty much the ideal material to create bubbles. There is a lot of money in bubbles. People will almost always pick a product that gives them lots of bubbles, or a “rich creamy lather” as my marketing colleagues would probably prefer to call it. I once gave a talk about shampoos to an audience of chemists and blew a large bubble to demonstrate how good at producing bubbles SLES was. It pleased them so much that I got a round of applause for it.
It has also been known for a long time that SLS irritates the skin. This is in fact so well known that when skin irritancy is being studied and you want to deliberately irritate skin, SLS is the generally agreed material used to do it. A lot of the skill of formulating shampoos and cleansers involves coming up with ways of maximising the bubbles while minimising the irritation.
It has recently started to become clear why SLS has this harmful effect. If you consider the structure of the skin, the outer layer is the stratum corneum. This is made up of dead cells that mover up from the basal layer becoming flatter and harder as they go. These cells are held together by small links, called desmosomes. These are made of protein and the rate at which these links break controls the rate at which the dead cells on the surface of the skin are sloughed off. This is controlled by an enzyme called stratum corneum chymotrypsin enzyme (SCCE) – which is the body’s natural exfoliating agent. It turns out that SLS interferes with this process altering the skins ability to lose dead cells
So applying products containing SLS and SLES to the skin is likely to disrupt the structure of the uppermost layer of the skin. The disruption probably won’t be very severe and probably won’t last very long, so I wouldn’t panic too much about it. But avoiding products that contain them is probably a good idea.
Methylchloroisothiazolinone Free Products
Interesting. Thanks. Do you know anything about Sodium Coco Sulphate – is it a milder version of SLS, or is it just the same thing under a more touchy-feely name?
Sodium coco sulphate and sodium lauryl sulphate are virtually identical. The only difference is that there is more variability in the length of the carbon chain in the molecule. They will both be equally irritating and are equally natural. I can’t think of any reason to prefer one or the other from the consumers point of view, but if you are a formulator you might find that the coco form might give you better stability in an emulsion. When I see sodium coco sulphate on the ingredient list of a product that claims to be in some way natural, green or safe I tend to assume that they are having a laugh at my expense.