How are PHAs different from BHAs and AHAs? 

The difference between PHAs, AHAs and BHAs lies in the molecular structure. PHAs have a larger molecular weight than AHAs or BHAs, which means that they do not penetrate as deeply into the skin but rather work exclusively on the skin's surface; making them less sensitizing and kind-to-skin as compared to other chemical exfoliants. 

How do PHAs work with other products in your skincare routine? 

PHAs help other skincare ingredients to penetrate more effectively into the layers of your skin, therefore boosting the efficacy of products used after them. 

As for mixing acids together? Yes, it can be done, however, if that is a little too strong for your skin sensitive skin, then try slowing things down to using just one acid or use them combined but less frequently. Because they are suitable for sensitive skin types

PHAs can also easily be incorporated into a routine that already includes products containing Vitamin C or Retinol; but again, be sure to start slowly to make sure there is no irritation.