Aw, shucks, 'tweren't nuthin.

Hexamine lasts nearly forever. The only thing I've seen fail is the binding agent (the "glue" that holds everything together in tablet form). In other words, the tablets can crumble a bit over time if left in the bottom of a pack. I've not experienced this myself, but I've read that damp climates can cause the binding agent to fail.

HJ