Beauty product expiration dates: How long you can keep your favorite products

Cleaning out your beauty cabinets may seem like an added chore, but it's essential, according to dermatologist Dr. Whitney Bowe. Using products that may be past their prime can cause them to appear streaky or not look the way they should, but even more -- use beyond the expiration date can actually cause serious health risks, Bowe warned.

Chemicals in certain cosmetics can break down and change over time and may cause irritation and inflammation in the form of a rash, Bowe said. In extreme cases, expired cosmetics can cause infections, as bacteria and even viruses can grow in some old makeup products.

In addition to throwing out old products, Bowe also recommends never sharing makeup, as germs are more likely to find their way into your cosmetics when you share them.

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Here are Bowe's guidelines for when you should toss or keep some of your favorite beauty 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.

Moisturizerand sunscreen

When it comes to moisturizer, the life span really depends on the packaging. If it has an airless pump, you can probably keep your moisturizer for over a year. If it is in a jar, Bowe recommends tossing it before a year is up, because you are constantly introducing new bacteria into the jar every time you scoop the product out with your hands.

Sunscreen can last up to three years if kept in a cool, dry, place. This is almost never the case, however, as people tend to take sunscreen to the beach and leave it on a towel or in a hot car. When exposed to heat, the chemicals in sunscreen can break down and either won't work or will make your skin break out, so Bowe recommends tossing your product before that happens.

Eyeliner and mascara

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.