An ingredient can go through the process of hydrolysis – a process in which “water reacts with the molecule to break down the molecule into its component parts” – when included in a formula in which the pH is too high or too low. For example, we don’t mix AHAs with niacinamide as the latter will hydrolyze at a pH lower than 6. Allantoin can hydrolyze at below 5. And some esters can hydrolyze lower than pH 5 or higher than pH 10.