Can I use a chemical sunscreen after a 20% salicylic acid peel?

It would be best to use a PHYSICAL blocker after this peel hwoever you shoudl be using growth factors like anteage MD and EMK to help you heal along with is clinical pro heal and siliagen gel. LED light thearpy like red light light stim.  the best physical blocker out now is ISDIN, sente, and reveskin elegance shade (see link to emeragecosmetics.com).  Best, Dr. Emer.

You can use this sunscreen after your procedure, but I recommend using a physical sunscreen instead. 

Yes you should be using a sunscreen after a chemical peel to protect your skin; however, it would be more beneficial for you to wear a physical blocker sunscreen that contains zinc and/or titanium dioxide. Hope this helps!