Sodium Lauryl Sulfate (SLS) and Sodium Laureth Sulfate (SLES) are cheap cleaning agents which creates a foam. It’s often used in bathing products like bathfoam and showergel, but also shampoo. 

Why we don’t use it: SLS can disrupt the skin barrier and cause irritation, by stripping away the natural oils. SLES is milder and often used to replace SLS, but it can still cause irritation.