Applying pH dependent actives
You probably heard about the "Thinnest to Thickest" rule when it comes to skincare application. Let's call that Skincare101.
It's time to move to Skincare201, and talk about an exception to this rule. Say, you have an "essence" or "serum" with AHA. AHA likes low pH, otherwise it's not ready to give you all the love you deserve. The same with L-ascorbic acid (LAA) based vitamin C, often, serums.
The rule is that actives that require such low pH to be effective are recommended to be applied straight after cleansing. You apply your LAA Vitamin C, for example, and then you wait. You wait for 15min or so (can be less or more -- it's a matter of preference. Then you get on with the rest of the routine.
But, you might ask the following question: "Maria, what if I have a vitamin C serum but it has tetrahexyldecyl ascorbate in it instead of LAA?" Good question. This one doesn't require a super low pH -- it is effective between 5.5 and 6.5, which means that you can apply it at the "serum" stage of your routine.
So yes, looking at the inci list is important, and can be the difference between "optimal" product application and "not so optimal" product application. Of course, it's also good to see what the manufacturers themselves recommend.