Everyone has products in their homes that are past their expiration dates, since everyone knows most things don't instantly go bad by some date printed on the packaging.

For myself, I'm more apt to use sensory clues than official expiration dates. Food is easy, if it's unappetizing, DON'T EAT IT. Beauty products are a little trickier.

While mascara doesn't necessarily go bad right at 6 months (standard guideline), I find it does start degrading sometime between there and a year. If your mascara starts getting thick and clumpy and becomes difficult to apply evenly, toss it. It probably has bacteria in it anyway.

I've kept lipsticks and lip glosses waaaay longer than the 1.5 to 2-year guideline, but they don't actually last indefinitely. The oils in them start to go rancid, so if you find an old tube of lipstick, smell it before trying it on. You'll know if it's gone bad.

Same thing with lotions, although I've found a wide range among brands with how long they stay good. Some start going after a year, others seem to stay fresh for a very long time. I have Dove self-tanning lotion that I've had since 2006, and even the tanning part still works. If the lotion has an "off" smell, go ahead and toss it. I don't think it will hurt you if you use rancid oil to moisturize your skin, but really, do you want to do that? Buy some new lotion.

Sunscreen actually does degrade quickly. Which isn't to say I don't use it past the expiration date, but I'm aware its potency is greatly reduced. So I'll get new sunscreen each year for days I'm actually in the sun. And I'll use up the old stuff on days I'll be outside, but in the shade. Yes, I can burn in the shade. But I don't need SPF60 to protect me, whatever the old stuff has degraded to works fine for me. But definitely buy a new tube of sunscreen each time you go to the beach-- it's worth $11 to not deal with the pain of sunburn on your vacation, isn't it? Use up the old stuff when you'll only be out for a little while mowing the yard or something.

I found a pretty comprehensive list of
expiration date guidelines online. From personal experience, there are some things I go longer on, but overall the guidelines seem reasonable.