Here's why it's important to throw out expired make-up & beauty products, according to Dermatology experts. Chemicals in certain cosmetics can break down and change over time and may cause irritation and inflammation in the form of a rash. In extreme cases, expired cosmetics can cause infections, as bacteria and even viruses can grow in some old makeup products.
Foundations
Liquid foundation usually lasts between a year and a year-and-a-half if stored in a cool, dry, place away from direct sunlight. If you notice that your product is separating into different phases or layers, this means it's time to toss it.
Powder foundations should last a few months longer than liquid foundations, or up to 18 months, if stored in the same conditions and in a sealed container. If you leave powder foundation open, however, it goes bad much more quickly. Powders are made with binding agents that absorb moisture, and if you leave the powder open, it dries out and won't work as well, and you may have to toss it much sooner than 18 months.
Retinol cream and Vitamin C serums
Retinol creams can last about a year if stored in a glass container and away from sunlight, as most retinols are light-sensitive, meaning if you keep them near a window they can break down quickly.
Vitamin C serums vary dramatically when it comes to stability, and are especially sensitive and break down quickly when exposed to light or air. They key is to keep a close eye on your serum: once it starts changing color (such as going from clear to brown), it is time to toss it.
Liquid eyeliner can be kept up to 12 months. You can keep pencil eyeliners essentially until they run out or the tip turns white or gray -- this can be a sign of mold. You can prevent this from happening, however, by sharpening the tip periodically, causing new bacteria to fall off with the shavings.
Mascara should be tossed every three months. If your friend ever borrows your mascara, however, Bowe recommends tossing it out and buying a new one, as the eyes are especially susceptible to infections.