system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: How come hand sanitizer has an expiration date? What exactly happens once it goes past it?
gpt
Also: the expiration date is set somewhat arbitrarily, and marks the end of the period of time tested. The test period is generally selected to account for storage time required for manufacturing and distribution, in a case like hand sanitizer, there's probably some consideration of the typical "lifespan" of a container in the consumer's possession. It would also assume recommended storage conditions; container closed, at room temperature.

Exceeding the expiration date simply means no data exists to support its continued efficacy, and it's likely to be good well beyond that date.