What is the shelf life of this?

thanks

I would keep it for about a year. It might be good longer than that, but I would not chance it with anything I put on my eyes.

What happens with your eyes when you put something expired?

Probably nothing. For this product, it most likely just looses its effectiveness. With other eye products that actually touch your eyes in any way (I am thinking applicators here) I would recommend replacing them more often.