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These days, many makeup items tell you upfront how long they're good for. They're usually marked with a MM/YY date that tells you when you should throw it away. If an item doesn't have a specific date, it may have a PAO (period after opening) mark that tells you how long the product is good for once you open it. The PAO mark appears as number inside a small jar symbol. 6M, for example, would mean that a product is good for six months after the date that you open it. Expiration dates and PAO marks are only guidelines. If you notice changes in color, consistency or scent prior to the dates on the packaging, you should still throw away the products. Some products may not have an expiration date or PAO mark, so it's up to you to use the standard guidelines to know when to throw them out. It can be difficult to remember when you bought a certain tube of lipstick or blush, though, so it's a good idea to put a label on the item with the date. That way, you'll know precisely when you should throw it away. Instead of labeling the makeup with the date that you bought it, figure out the date that you should get rid of it according to the general guidelines and write that on the table that you place on it. If you have items in your makeup drawer that don't have expiration dates or POA marks, and you haven't labeled them, all hope isn't lost. There are several apps, such as Beauty Keeper, Check Fresh, and Check Cosmetic, that helps you figure out when an item was manufactured. All you have to do is input the item's batch code, which is a number usually printed somewhere on the product.

Summary:
Notice the expiration date. Label items with date of purchase. Use apps to help keep track.