You should make a habit of smelling your makeup because it’s easy to tell if a product has gone bad. It is easier to tell with liquid products and lipsticks because bacteria can get in and start to let the product go bad.
If the consistency of your makeup changes then it’s another sign that you should throw it away. It is easier to notice in foundations because it will separate or become thicker, but powders will start to crumble; other products might get clumpy or they might not blend properly anymore.
Makeup is prone to oxidation, per MasterClass, so the longer you have the products, the higher the chance they oxidize and change color. It’s important to close your products after you use them because they can’t be exposed to air for too long.
Even unopened makeup can go bad, so if you’re someone who likes to stock up, just make sure you’re not keeping it for too long. They can last up to 2-3 years if stored properly, but after this time, it’s best to simply replace the product.
If you start breaking out after using a product for a while then it’s a sign the product has gone bad. A common reason makeup will make you break out is mold, even if you can’t see it; another reason is if the oil has separated in foundations and concealers, which clog your pores.