Do pH strips expire?

My pH strips are a couple years old, and due to a move they were sitting in a non-air conditioned storage facility for a couple months this summer. I tried to use them tonight but when I dipped them in the wort they turned a strange color green that’s not on scale. Is this due to the age and high temps, or could this be from something else? Is it time to get new strips?

Yes, they do have a shelf life. They don’t last too long. Couple of years old and less than optimal storage would indicate new strips are in order.