Sunscreen before or after moisturizer, etc…?

A chemical sunscreen
should go on clean, bare skin first, you need to give it
time to be absorbed, because in order to be effective, it must interact
with skin cells. Apply a serum next and, finally, moisturizer if you need
it.

When it comes to physical (mineral) sunscreens, there is no doubt that they should ALWAYS be applied as the last step of your skin care routine but before make-up. When it comes to chemical (or combo) sunscreens, there certainly seems to be some debate about when to apply them. Most dermatology and skin cancer organisations state that any type of sunscreen, regardless of whether it is physical or chemical, should always be applied as the last step in your skin care routine but before make-up. The debate seems to be among dermatologists, some of which are now arguing that chemical sunscreens should be applied to bare skin before anything else. There are 2 reasons they usually give:

1. When testing SPF, sunscreens are always applied on bare skin. The argument is that, in order to achieve maximum SPF, we should apply sunscreen the same way as in testing. While there haven’t been any studies on the potential of serums and moisturisers to interfere with the chemicals in sunscreens, I doubt that they would have a major effect.
2. The active ingredients used in chemical sunscreens need to bond with skin cells in order to work. I’ve never seen any research that suggests this and, to be honestly, it sounds ridiculous to me. Chemical sunscreens work by absorbing UV rays so it doesn’t matter how close to the skin they are. Frankly, you would want them to be as far from the skin as possible in order to minimise irritation and absorption.

Based on the above, I would suggest always applying sunscreen as the last step in your skin care routine but before make-up.

I’m so glad I don’t have to deal with that situation, being a guy. It’s always puzzled me too. It seems the best you can do is reapply a powder with SPF throughout the day, although that is of course not very ideal.