Hand sanitizer expires when the amount of the sanitizer's antibacterial agent drops below 90 percent of the stated level. Although legally expired, a sanitizer may still have some effectiveness remaining after the printed date.
Legally, all products sold on stores must have a "shelf life" or an expiration date. Generally the expiration date is printed on the bottom or back of the package. If there is no expiration date printed on the package, the product is good for three years from the date of manufacture. Sanitizers that have added scents or colors may expire sooner and should have a date printed.