MSM

A small sulfur-containing compound, methylsulfonylmethane, known in skincare by its short name MSM.

What it does: Used in calming toners, serums, spot creams and vitamin C serums to help keep stressed or breakout-prone skin in good, comfortable condition.
How often: Daily in toners, serums and creams, at the frequency the whole formula calls for; spot treatments follow their own directions.