Can you apply a benzoyl peroxide/glycolic acid serum in the morning and tretinoin at night?

Thanks for your question.  You will probably do fine using both the benzoyl peroxide/glycolic acid serum in the mornings in addition to your nightly tretinoin.  If you are very tolerant of the tretinoin and you don't get peeling or redness or sensitivity, you can go ahead and start the morning serum and see how it goes.  If you live in a very dry climate without a lot of humidity, you might want to start slower and use the morning serum every other day or every third day and gradually build up to daily use.  Always use a good quality sunscreen whether you spend a lot of time outside or not - those products can increase your sun sensitivity.  If you tan or burn the face, you'll be undoing the good effects of the tretinoin as far as treating fine lines, sun damage and brown spots.  Best of luck!