It's a sad truth for those of us who stockpile make-up - it does have a shelf life.
I used to have a fairly obscene amount of MAC - mostly eye shadows, liners and lipsticks - when I had a disposable income. A few months ago, I had to go through the painful process of tossing out two thirds of it. Not because I'm utterly anal, but I had honestly owned the stuff for a few years, and if anything, the lip products had to go. I don't regret buying it all in the first place. I did use it. But the fact is I had so much choice that the only products I ever used up were the blackest of shadows and liners. The blues, greens and purples got enough play, but not quite enough for me to scrape the bottom of the eye shadow pan.
Whilst there is a little leeway to be given for all make-up expiry dates, I do believe in buying fresh versions when it's necessary and feasible. Here are some general guidelines for expiry:
Foundation: 6-12 months
Blush (powder): 2 years
Blush (cream): 12 months
Eye Shadow (powder): 2 years
Eye Shadow (cream): 6-12 months
Eyeliner (pencil): 2 years
Eyeliner (liquid): 3 months
Mascara: 3 months
Lipliner: 2 years
Lipstick: 2 years
Nail Polish: 1-2 years
Perfume: 2-3 years
Of course, none of these are set in stone, and some products will randomly go bad on you within a few months. Others might last for years. I know certain people with vintage make-up collections that are still good to use. As a rule, cream and liquid products such as mascara and lip gloss will spoil much faster than powders. Powders are generally not the happiest place for microorganisms to grow, so keeping these longer is usually fine. Cosmetics companies often have their own expiry dates on the packaging, so feel free to refer to these as well.
Meanwhile, there are things you can do to preserve the life of your makeup. As someone who is training in make-up artistry and beauty therapy, hygiene is very important whether I am working in the college studio or freelance. Here are some tips. They don't include things like not double-dipping, because that's pretty much a trade rule to avoid cross-contamination between clients.
-clean your make-up brushes often. I have a decent collection of horsehair brushes from MAC and from my college's own brand. I have a sweet little spray that you can use on the brushes, wipe with a tissue and then they dry within a minute or so. I do this between clients, but I like to fully clean my brushes at least once a week with the MAC brush cleanser. I don't recommend the little sponge-tip things you often get inside make-up compacts. They're no good for application and they harbour germs very easily - if you use them, just get rid of them afterwards.
-don't wet your eye shadows. It's true that applying shadows wet increases colour payoff and intensity. If you want to do this, swish your brush into the eye shadow and then dampen the brush under the faucet before applying. If you're tempted to re-dip your damp brush in the shadow, you could try an alternative - apply the shadow to your eyelid with a dry brush, then use a damp brush to blend. A bit of a fuss, but worth it to make sure your powders don't go all clumpy.
-sharpen your pencils regularly. This is a quick and easy way to get rid of bacteria on the tips, and obviously gives you better application as well.
-don't pump your mascara wand. This will force air into the tube which makes the product congeal more quickly. Mascara lasts a short enough time as it is!
-I'd say store your liners, lipsticks and polishes in the fridge. But that might be a) confusing b) annoying or c) not possible, depending on who you live with and how full your fridge tends to be. This method does help with shelf life and ease of application however.
-check your products! Liquid and cream products tend to smell quite odd when they go 'off', plus their consistency also changes - you'll find it difficult to apply them evenly, they will seperate... and generally you will just know.
I hope these notes are useful in preserving your gorgeous beauty collections (and in turn your gorgeous faces)!