Technically, deodorant doesn't have an expiration date. It's likely antiperspirants will work for years as well. But to be on the safe side, you should probably replace the stick every three years, if you still have it.

Is Certain Dri bad for you?

Despite what you've heard, aluminum—in any of its many sweat-blocking formulations—doesn't seem to pose serious health risks in clinical studies.

Why does certain DRI burn and itch?

It does itch a few minutes after application but it's because it's literally closing your pores. If you can deal with a little itch under your arms for a few minutes it's definitely worth the discomfort.