Retin-A or tretinoin makes you a little more sensitive to the sun meaning you will burn more easily. As long as you're wearing your hat and sunscreen which you should always do (for skin cancer, wrinkle, and sun spot prevention), there is no problem. You don't have to go crazy about it as the increased risk of a sunburn is quite modest. ~ Dr. Benjamin Barankin, Toronto Dermatology Centre.
Thank you for your question. After use of Retin A your skin becomes more sensitive to sunlight and will burn more easily. High spf sunblock in addition to wearing your hat and sunglasses will certainly reduce the likelihood of sun burn. The increased risk of sun burn may be modest but could also be impacted by the local climate.