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.