SLS stands for Sodium Lauryl Sulfate. It is typically found in beauty products, such as shampoos, soaps and cleansers, and is what makes your favourite fancies foam, thanks to its emulsifying and foaming agents.
SLS has received a lot of press recently, some of it exaggerated, and some if possibly true, and as is the case with Paraben, it is becoming increasingly difficult to determine what is Fact and what is Fiction. And the reason for the frenzy is down to the fact that SLS can cause skin irritation, as well as allergic reactions.
I don’t know how high the chance is of getting irritated, because I’m not an expert, but there are certainly growing amounts of companies that have jumped on the scaremongering bandwagon, by promoting themselves on them being SLS-Free. Also plenty companies legitimately don’t include SLS, so there are plenty of products that should be safe to use.