Many US products also use this system (mostly because they don't want to print different packages for different countries) but it is not required. Shelf life of cosmetics is important because even an effective preservative package will lose efficacy after a certain amount of time and at that point the product can become contaminated with bacteria and molds. Also, all oils will go rancid given enough time. Some oils go rancid very quickly, like grapeseed oil, while others are stable for a long time, like mineral oil. All Natural products have a much shorter shelf life than conventional products and are more likely to lose their preservative efficacy more quickly. Manufacturers determine the appropriate shelf life based on the shelf life of the raw materials and internal stability testing. Unfortunately manufacturers can't account for the variable of how the consumer uses the product. For example, say you have a face cream packaged in a jar. Customer One stores the product in a dark cabinet in a non humid room, washes their hands before using it and re-caps the product tightly after each use. Customer Two stores the product on the counter in their bathroom, doesn't wash their hands before use and just sets the cap back on without screwing it down. Customer Two's product is FAR more likely to grow bacteria and mold than Customer One's. There are real dangers to using out of date or expired beauty products
- Skin infections
- Increased breakouts
- Dry skin
- Eye Infections
- Rashes and allergic reactions
Eye products like mascara should be tossed after 4-6 months at the most. If you have a mascara that is clumpy and won't go on smoothly, do NOT add water or saliva to it to thin it down. Chuck it.
Liquid face products like moisturizers and foundations should be good for 1-2 years.
Powder products like blush, loose or pressed face powder or eye shadow should last for 2-3 years under appropriate storage conditions.
If at any time you notice an off odor, thinning of the product or separation in an emulsified product, toss it out immediately. It's also not a good idea to share products, it increases the likely hood of contamination. Tester products in stores are also never really a good idea. You have no idea how many or how the people before you have used the product.