:confused: hi, a Mac employee tell me that I could keep my eye shadow for 10 years..

Yes, they can expire. But if you store them well (in a cool, dry place) they should stay in a usable condition for a long, long time. Cream products expire a lot faster than powder products.

See this for more information: http://www.specktra.net/showthread.php?t=25425

I wouldn't necessarily say that powder products "expire" unless they have SPF in them. It's likely that if you've had it for awhile, the consistency will change a bit, and it could lose its color, the texture can change, and so it probably won't apply the same way.
My person "guide" to when to chuck and when to keep:
Lipglosses, if I don't use them up within a year, I chuck them. Especially if they smell weird. FE, MAC Lip/Lustreglasses have a bit of a vanilla smell to them. If you can't smell that or it smells like something else, toss it.
Lipstick: ^^Same thing. Or if it changes texture.
Cream face products: I give them about a year or two, if they're cream blushes etc.
Mascara: Replace every 6-9 weeks.
Liquid eyeliner: I replace mine every 6 months. Fluidlines or gel/pot eyeliners are an exception because the applicator doesn't reside in the product like regular liquid liner does

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For cream, fluidy cosmetics, there's usually a symbol that looks like an open white jar with a lid on the packaging of the product, wether the card package or the product itself. That simbol usually has a number in it, it can be 3, 6, 9, 12, 15, 18, 24, etc. These numbers symbolize how many months does the product last after it's been opened for the first time. Fluid to cream and stick foundations last for a year (usually), concealers can last from 6 months (like Le Touche D'Eclat) to a year (MUF Lift Concealer), makeup primers can last a year to a year and a half. So, whenever purchasing something that is not powder, always check the symbol and put a little sticker or a mark for the month you started using it.

Some people have extremely resistant complexion and don't suffer if they use their products over the time limit, but people with sensitive skin, like myself, the consequences can be disastrous. From breaking out to turning red, hot and slightly swollen, it's not a pretty sight.

Hope this helped.

good to know, I can finally justify my reasons for cleaning my traincase out every year to my mother LOL! She thinks I'm throwin' money out the window and I'm like...mom they're too old haha.

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Jessica
Representing the San Francisco Bay Area *the place I call home* 8)
...and yes, I say HELLA