If you’re a skincare nerd, you may know that different skincare oils have different fatty acid profiles – that is, they differ in terms of which fatty acids they contain e.g. linoleic, linolenic, oleic and lauric acid. The fatty acids have interesting properties. For example, lauric acid is strongly antibacterial, and works better than benzoyl peroxide against Cutibacterium acnes bacteria. Oleic acid is a barrier disruptor, while linoleic acid can fade pigment. So it sounds like skincare oils could be interesting active ingredients or irritants, alongside moisturisation! Related post: Do oils make your skin less oily? The myth of rebound oil But there’s a catch: in oils, these fatty acids aren’t actually acids at all. They’ve undergone a chemical reaction to form new substances called triglycerides. These triglycerides can be broken down to form the free fatty acids again under the right conditions: during digestion, and in the process of saponification in soap-making. But does this happen on the surface of your skin? I’ve been wondering about this for a while, and I’ve had a few chats on and off with fellow nerd Stephen of Kind of Stephen over the years but we never really came to any firm conclusions. I finally sat down recently and dug up all of the papers I could find on fatty acids and combed through them all to try to make some sense of it (there were literally about 400 papers that I sorted through, which is why I couldn’t bring myself to do it earlier… I probably didn’t need to go through so many, but I like to be extra thorough to convince myself thrice over before trying to convince anyone else!).