There is a sunscreen in your bathroom drawer that you bought last May. One holiday, a few months of walking to the station, and then autumn arrived and it went in behind the hair ties. It is September again and the bottle still has weight when you shake it. Almost everyone does the same thing next. Turn it over, hunt for a date. Right instinct, wrong number. The date stamped on a cosmetic is normally a shelf life counted from the manufacturing date, and it describes a bottle nobody ever opened. Yours has been open since...