It's very important to know the self life of the cosmetics that you are using because it will decrease your chances of infecting with bacteria. Here's a helpful list to help you keep track:
What is the Shelf-Life Cosmetics:
Mascara
Shelf Life: Three-six months
Mascaras should always be used fairly quickly once they're opened because they're easily contaminated by the pumping action of the brush. This can force bacteria further into the container where the moist, wet environment is ideal for bacteria to thrive.
Moisturizer
Shelf Life: Three-12 months
Moisturizers should be used up quickly, especially ones that contain essential oils and botanicals (check ingredients on the label). The best idea is to buy one moisturizer at a time and use it everyday. This is more important with natural ingredients such as plant extracts that can quickly lose their efficacy after a certain time and go off. Check the use-by date if you're not sure when yours should be chucked.
Foundation
Shelf Life: Oil-Free Foundation (12 months); Moisturizing, Cream or Compact Foundation (18 months)
Again, it's a good idea to use foundation quickly. Oil-free ones have the shortest shelf life because they tend to dry out quicker than other types.
Powder
Shelf Life: Two years
Although powder will actually last longer, two years is the longest you should really keep it. After that, it can start to get a bit dry and, in the case of pressed powder, it may not go on as smoothly. This is unavoidable, as powder mixes with natural skin oils left on the sponge. As a general rule, loose powder can last up to three years in the right conditions.
Concealer
Shelf Life: 12-18 months
Stick concealer lasts the longest of any type. You can tell it's had its day when it starts to get dry and no longer goes on smoothly. Liquid based concealers may start to separate or go lumpy when they're going off.
Blusher
Shelf Life: Powder Blush (two years);
Cream Blush (12-18 months)
After two years, powder blushers may start to get a bit dry or develop a 'slippery' texture, caused by mixing with natural oils from skin. Also, once the colour changes it's no longer in its prime. Cream blushes have a shorter shelf life because they contain more emulsions, which are less stable and break down over time. However, you'll find you use these more quickly anyway.
Eyeshadow
Shelf Life: Powder Eyeshadow (two years); Cream Eyeshadow (12-18 months) Powder eyeshadows can last for ages because they are mainly pigmented pressed powder. Cream eyeshadows have a shorter shelf life because, like cream blushes, they use emulsions that break down over time.
Eyeliner and lipliner
Shelf Life: two years
Eyeliner and lipliners are the workhorses of cosmetics. They last for ages because sharpening them regularly goes a long way in preventing bacterial growth.
Lipstick
Shelf Life: two years
Lipsticks are generally quite long lasting because of the way the pigment and fat are formulated together. Don't be put off if tiny bubbles appear on the surface - these are just moisture drops and can be wiped off. Lipgloss Shelf life: 18 months because it is formulated differently.
Fragrance
Shelf Life: 18 months-two years
Fragrances carry little risk of becoming contaminated because they usually contain alcohol, which is a natural preservative. (NOTE: I find that the higher quality perfumes last much longer than 2 years if stored properly out of sunlight and with the cap on)
Makeup will last longer safely if you clean your tools (brushes, applicators, sponges). And never share makeup. Dirty tools and sharing will contaminate your makeup with bacteria.
