Some deodorants carry expiration dates on their packaging because they also include antiperspirants, but deodorants not containing antiperspirant do not expire. The aluminum salts in antiperspirant expire, but solid deodorant ingredients last an indefinite amount of time, according to Outside Online.
Deodorants fall under the category of cosmetic products, and manufacturers usually recommend discarding old products within a year of opening because of risk of bacterial growth. However, deodorants fight bacteria, so the risk of this is almost nil. Over time, the fragrance is likely to fade, but the products are likely to remain safe to use over the long haul, as stated by Outside Online.