Ingredient Lists 101: Surfactants
Understanding the Controversy Around Sodium Lauryl Sulfate (SLS)
Disclaimer: I am not a doctor, just a cartoon deer on the internet with a background in chemistry and a hyperfixation on skin. This is not medical advice.
On my quest to demystify skincare, I was inspired recently by a video of friends playing with a concept called surface tension. You can think of surface tension as the characteristic water displays in adhering to itself, but it also carries importance in skincare too! Common knowledge is that water and oil don’t mix - so what happens when we want to formulate a product that will give us the benefits of both?
Enter surfactants! We’ll start with a science lesson:
Surfactants are a curious class of molecules with both hydrophilic (“water loving”) and lipophilic (“fat loving”) regions, and as such, you’ll often see them in soaps and detergents. In fact, surfactant is actually short for “surface acting agent”.
The nature of surfactants allows them to interact with both oil and water by forming micelles:
Surfactants have many functions, but let’s pick an easy one everyone can relate to: say you’ve been cooking, and you spill olive oil on your hands. Trying to wash it off with just water wouldn’t work well, right? We know that’s because oil and water don’t mix, of course. If we add in a surfactant (ie. soap), the lipophilic region of the individual soap molecules will surround the fat molecules from the olive oil while leaving the hydrophilic region exposed. Then, if you wash your hands with water, everything will come off. Simple! Micellar water and shampoo work similarly.
Now we understand that surfactants are nothing to be afraid of, right? Okay science lesson over. Here’s the stuff you actually need to know:
You can often spot surfactants as the chemical name may include some derivative of “sulfate”. Other common surfactants you may come across include dimethicone, cetaryl alcohol, sodium stearate, stearic acid, cetrimonium chloride, polysorbate ester, and cocamidopropylamine oxide. Of course, if you’re unsure whether an ingredient is a surfactant, a quick Google search will give you the answer.
If you have sensitive skin (read: your skin gets irritated, turns reddish easily), you may need to be careful with products with higher concentrations of surfactants. A personal heuristic I have is avoiding cleansers where surfactants are listed among the top ingredients as they will err on the side of harsh. There is evidence that sodium lauryl sulfate (SLS) and ammonium lauryl sulfate can cause irritation, but the Cosmetic Ingredient Review (CIR) panel has concluded on two separate occasions that neither cause consistent issues in cosmetic formulas as they’re most commonly formulated at < 1% concentration. Further, there has been misinformation spread around the internet (surprise, surprise) that SLS is carcinogenic. As of me writing this in April 2022, there is no conclusive evidence that sodium or ammonium lauryl sulfate are carcinogenic. Based on your personal comfort level, you may wish to avoid either or both.
Brands are rarely transparent about the actual concentrations of ingredients included in their formulas (except for one of my favorites, Good Molecules). One of my hacks to get around this is that at concentrations greater than 1%, ingredients are required to be listed in descending order of concentration. We can use this knowledge to gauge the relative concentrations of ingredients. For example, if a product lists 2% salicylic acid, you can use that as a benchmark to gauge the concentration of anything listed after salicylic acid in the ingredient list.
That’s all for now! Happy skincare!
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