Everyone should always wear sunscreen on their face, whether you have acne or not - - even on cloudy days. Our faces are the most exposed part of our bodies, and they need to be protected from cell-damaging sunlight and the potential for skin cancer down the road. People who use topical vitamin A, which is also known as retinol and is found in products like Retin-A, will experience even more sensitivity to the sun.
Use a moisturizer with sun block each morning. If you'll be outside in the sun for an extended period of time, bring along an additional non-comedogenic sun block formulated for faces, since the SPF in your morning moisturizer isn't formulated to last all day at the beach. The sun block won't act as a moisturizer, but it will keep sensitive skin from burning -- and causing a host of new problems for your acne-prone skin.