I know I let most o fine sit wayyyyy to long. I have seen different articles suggesting anywhere from a few moths to a few years to keep various products once they are open, but I know tend to forget all that really easily. One thing I did was to pare down to what I really use for cosmetics. Then I am more likely to use up a product before I should toss it out.
I hate to throw out cosmetics or skin care stuff! I think I hate to waste the money, then I let it sit in the drawer for 5 years-lol. We moved into our current house 8 years ago so I'm sure some of the things in there are that old at least.
I don't like throwing away cosmetics. If I bought a new one, I gave the old ones to my sister, she loves receiving hand-me-down cosmetics from me. I don't let my cosmetics sit in my drawer for too long.