Play-Doh does not have an expiration date. If kept moistened, the Play-Doh compound may be used many times. However, if the compound is hard, it is likely to crack when manipulated.
Adding some water to the Play-Doh compound one drop at a time helps keep the compound moistened. Alternatively, the Hasbro website recommends wrapping the Play-Doh compound in a damp paper towel and leaving it overnight in a closed container. If left to dry completely, the compound hardens, and it may not be usable again.
Play-Doh is the top seller of modeling compounds. Between 1955 and 2005, Play-Doh sold more than 2 billion cans worldwide.