It can be hard to part with some of the products in your bathroom cabinet, especially if you splurged on them. So how old is too old? When in doubt, toss out anything that you haven't touched in a year, advises Yale-affiliated dermatologist Dr. Alicia Zalka. "Both because it's getting old and, more importantly, because if you haven't used it all year, you don't love it." For product by product tips, read on.