For most skin and body care products, there is an easy way to find out how long the skin care ingredients are good for. Simply look on the back of the container. Many times you'll see what looks like a skin care product tub that is opened with a number on it. The number is usually 6, 12, 24 or 36. What this means is that you can safely use this opened product for the number of months it says. But let's remember that dipping your fingers into product does bring bacteria into the mix. Always us a spatula, or my favorite, a baby spoon that you can get at the drugstore.
Now, do I always throw away a lotion if it's over a year old? Not usually. Many times it's still fine to use as long as the product is not separating or looking a bit "off". Just use your best judgement and if you think it's time to toss it, it probably is. Pay more attention to the dates on your facial products, as they usually have special ingredients to help protect your skin. If your product doesn't have an image on the back, assume it is probably no more than 12 months unless stated. If your product contains organic ingredients or you purchased it from a small company that produces their products after your order is placed, make sure you ask what the shelf life is. In some cases, the shelf life is very small due to the lack in preservatives.
Unopened products that are still sealed usually have a shelf life of 3-5 years or more, so don't be concerned about the products on the shelf. As long as they stay sealed, they will last many years. The time only starts counting down when you open it.