Moisturizers, sunscreens, and other skin care products can be expensive, so it makes sense that you’d want to keep them as long as you can. But how long is too long? Is that jar of cocoa butter or tube of zinc oxide from last year is still good?
It would be helpful if every product had a “use by” date, but the FDA actually doesn’t require manufacturers to include expiration dates on labels for products that are proven to be shelf-stable if they last 3 years or more. So, if personal care products don't have an expiration label, the general industry consensus is that these products should last for 3 years. But bear in mind that when you buy these products, you don't know how many months they've been sitting on the store shelves, in the distributor's warehouse—or even in the manufacturer's plant before that.
When products break down, our eyes and nose often give us clues. The product may smell funny, separate, change texture, or change color. Also, bear in mind that some personal care products such as sunscreens and facial moisturizers contain skin protectants that may oxidize and spoil more quickly when exposed to air. The shelf life some of these products, such as those containing benzone, titanium dioxide, or zinc oxide, essentially begin to "spoil" after you open them. The shelf life of these products has been a much debated issue, with some experts arguing that these products expire as quickly as a few months after they’ve been opened. Sure, you could get away with using last year’s sunblock, but be advised that you may not get the same amount of protection from the sun that you would if the product were freshly opened.
Bottom line: unless the product has an expiration date on the label, these products generally should be shelf-stable for 3 years. But proceed with caution and look (and sniff) for any signs of breakdown before you use them.
Here is a link where you can read more about expiration dates.