What is the 1% rule in skincare?

The 1% rule (or 1% line) in skincare refers to how ingredients below 1% concentration are no longer required to be listed in strict order on a label. Many active ingredients — such as retinol, acids, or vitamin C derivatives — can be effective even at concentrations around or below 1%. That said, not all actives work well at such low levels, and increasing concentration beyond that doesn’t always improve results; it may lead to irritation or instability. In practice, it’s wise to start with lower concentrations, observe how your skin responds, and increase slowly if needed.