SLS (sodium lauryl sulfate) and sensitive skin
Should you avoid SLS in your cosmetics if you have sensitive skin? This question has spurred quite some debates in skintellectual circles recently. The line of debate primarily lies between dermatologists and cosmetic formulators. Dermatologists (including our advisor Dr. Sandy Skotnicki) have been advising for a while to avoid SLS-containing products if you have a sensitive, reactive skin. Cosmetic chemists, on the other hand, insist that products with SLS can be formulated to be non-irritating. Here are our thoughts on the matter.
SLS is the industry standard skin irritant. It is the go-to irritant researchers use as a control group for skin irritation studies. It is also used to evaluate the sensitivity and accuracy of different methods used to detect irritant skin response. For example, in this in-vivo study , different patch test systems were evaluated for detection of irritant skin reaction to water, 0.06% concentration of SLS, and two cosmetic products. The choice of the patch test system mattered: while the first one tested did not show a meaningful difference between the skin reactions to water and 0.06% SLS, the second one detected the stronger reaction to the SLS.
What does it mean for us, consumers? We think that in the case of the SLS debate, it is more prudent to follow the advice of the dermatologists and err on the side of caution - that is avoiding SLS in your products if your skin is sensitive. We have data to confirm that SLS is irritating to the skin even in small concentration, even though not all test methods used can detect it. Besides that, most cosmetic products are not tested using the cumulative irritancy testing - so we are not sure what data do cosmetic formulators have to show that their SLS-containing products are indeed less irritating than, let's say, the 0.06% SLS emulsion used to induce skin irritation in the study cited above.
In addition, SLS does not have a unique benefit for the skin - it is simply a cleansing and foaming ingredients, and it can be substituted by hundreds other ingredients many of which are milder. So there is no particular advantage to taking the risk and using SLS-containing face and body washes if your skin is reactive. Of course, as always, individual differences matter: if you are allergic to coconut-derived surfactants (like cocamidopropyl betaine, an allergen on the year in 2004) that are often used in cleansers marketed for sensitive skin, a product with SLS might still be a safer choice for you.