"I think that gradual daily exfoliation is better than a full-on peel," said Julia. "In terms of acids, in the US, there is no level, literally no cap on it, and some products are formulated at around 30%. That was something we wanted to be mindful of when creating Prism, £52 , which is based on a rainbow of natural acids (5%). We wanted something you could use daily and not be worried about literally burning your face off." If your skin is super oily and prone to congestion, R29 recommends choosing a higher percentage, like The Ordinary's Glycolic Acid 7% Toning Solution, £6.75. Skin prone to whiteheads and larger spots might do better with a swipe of INKEY's Glycolic Acid Liquid Toner (10%), £6.99 , nightly.