Some hair products have an expiration date or period after opening (PAO) timeline that indicates how long the item will last. But according to Hair.com, the FDA does not require beauty product distributors to explicitly place a best-buy, expiration date, or PAO indicator on items' packaging.

But even if your item has a PAO number, it isn't necessarily easy to read and understand. The symbol for a PAO number is a small jar with an "M." On that jar, there will be a number. That number indicates how many months after opening your product will stay good, per Reader's Digest. If the symbol has a "12M," your item will last a year after opening it, if it has "6M," it will last six months, and so on.

If your product has no date that signals it is past its prime, you'll need to pay attention to certain features to see if it has expired.