I am wondering if I could use Hydra-Cool Serum 30 minutes following my Differin gel. My face is very red from the Differin and applying anything to it makes it more red. My dermatologist recommended a steroid cream but I do not want to use that.

Since you seem to be having side effects from the Differin gel, you should consult with your dermatologist again. If the skin surface is not broken or open, Pro-Heal Serum Advance+ and Extreme Protect SPF30 could be helpful in this situation. Please discuss this possibility with your dermatologist.