A. The expiration date is three years after it's manufactured, says James Spencer, MD, associate professor of clinical dermatology at Mount Sinai School of Medicine. (There should be an expiration date on the package.) But there is no consensus about how long a sunscreen retains its effectiveness after the bottle or tube has been opened. So if you have an open tube left over from last year, pitch it. A new tube of sunscreen will cost you less than $20. Not having to endure skin cancer treatment is, well, priceless.
Bottom line: To be on the safe side, buy new sunscreen every year.