People save money for months, just to splurge on one piece of makeup that they think will last them a while. And if they only use it on special occasions, maybe it will. But that doesn’t necessarily mean that it should.

Makeup is expensive. So when you spend $50 on a single eyeshadow palette, of course you want to make the most of it. But keeping it too far past its Period After Opening (PAO) can become dangerous.

Although the FDA doesn’t require cosmetics to have expiration dates on their labels, most products will have a PAO, which serves as a guideline for when the product should be thrown away. The PAO is a small icon that looks like an open container. It’s accompanied by a number followed by an “M,” which tells you the number of months that a product is safe to use after it has been opened.

Makeup usually lasts from four months to two years after it has been opened, depending on the type of product. Mascara can last from four to six months, while lipstick and blush can last up to two years. In general, powders will last longer than liquids.

The Urban Decay Naked Eyeshadow Palette costs $54 and has a PAO of 12 months. This means that despite the expensive price tag on this product, it should be thrown away after one year, regardless of how much eyeshadow is left in each pan.

Though this may seem like a waste of money and product, it’s important to listen to the PAO. A study from the Journal of Applied Microbiology found that nine out of ten makeup products contain bacteria capable of causing illnesses and infections.

Your makeup could be hiding bacteria like Staphylococcus Aureus (Staph), E.coli, Pseudomonas Aeruginosa, and Citrobacter freundii, among others. When these types of bacteria come in contact with your mouth, eyes, nose, open cuts, or pimples, they have the ability to cause dangerous skin and eye infections. And, the longer a product is kept past its PAO, the higher this likelihood gets.

However, there are a few things that you can do to keep a product as safe and clean as possible. For one, never share makeup, especially products that are used close to your eye. When you share makeup there is a high probability that you are also sharing germs, which can lead to an infection.

Storing makeup properly helps reduce the risk of bacterial growth. Make sure that all covers are screwed on tightly. For mascara—don’t pump the wand in its tube to get product on it. This forces air and bacteria inside. And, don’t leave makeup anywhere too hot, like a car. Bacteria and fungi tend to prefer warmer environments.

Makeup applicators and brushes should be cleaned regularly, especially beauty blenders. Research published in the Journal of Applied Microbiology stated that makeup sponges have the highest levels of potentially harmful microbes. Despite this, over 90% of makeup sponges are never cleaned by their owners.

Makeup applicators should be cleaned weekly, and thoroughly washed once a month. This can be done using dish soap or a makeup brush shampoo, which can be bought at stores like CVS, Target, or Sephora.

You can also clean the products themselves. For products like lipstick, lip liner, pencil eyeliner, and concealer sticks, wipe the surface with an alcohol wipe. Pressed powders and cream makeup can be sprayed with isopropyl alcohol, which you can buy at any drugstore.

Lastly, although it may seem obvious, make sure that your hands are clean before you apply any makeup. Every time that you dip your fingers into a product you are introducing microorganisms.

Even with this knowledge however, it’s likely that at least a few out-of-date products will remain in your makeup collection. It can be painful to throw away a product that you spent your hard-earned money on. But if you are going to keep a product past its PAO, it’s important to keep an eye out for the warning signs that it has gone bad.

In all your products you should look out for a change in smell, texture, or color. In liquids, like mascara or concealer, watch out for clumping or drying out. If you notice any of these changes you should throw the makeup out immediately.

So next time you’re planning to spend big bucks on a piece of makeup, check out the PAO. Will you really finish that product by then? If not, consider investing your money into something that will actually last, without any risk.

Do I Really Have To Throw Out My $50 Palette?