If you have sensitive skin that tends to react to the RA & become irritated, you can apply the HQ first then apply the RA over it. I have used both mixed & layered RA during the day w/o any difficulties whatsoever BUT you must really use an excellent sunblock & avoid the sun if you choose to do this. I used the blend 2x/day for the 1st week of returning to this routine in order to boost exfoliation. During the time I was trying out experimental blends, I was not using the RA & I wanted to purge off any accumulated dead skin. After accomplishing this, I returned to using HQ/ Sunblock in the morning & HQ/RA B4 bed at night. It was the right thing for my skin.