How long should you keep your makeup? There are recommended lengths of time for each cosmetics type but I have to admit, I don't follow them. I just have one general rule: if the product starts to smell rancid, separate, or just stop working the way it should, then in it goes to the bin!
Expiration dates for me are suggestions at best. I find that a product's shelf life is ultimately dictated by the limitation of its fomulation. For example, wet makeup like mascaras and liquid liners simply flake and dry up after four or five months. Lipsticks and glosses will start to thicken and just feel generally weird after two years. The waxes and oils in the formula will naturally dry up the more you use them, and you'll notice this when the product starts to separate (i.e. sweating lipstick, stringy gloss). The smell is the final giveaway though!
Gel products dry up faster than cream products, but you can tell if they're no good by checking the texture.