By Sarah Walter
Updated Mar 14, 2015 @ 8:02 am
Credit: Getty Images

Unlike that gallon of milk in the fridge or bottle of Motrin in your medicine cabinet, beauty products don’t come emblazoned with a clear expiration date, yet many of us hoard them way past due. As hard as it is to let go of that mascara you rely on (yet is starting to smell a bit funky), or an eye palette that’s slowly been collecting dust, sometimes you just have to let go. If kept for too long, products not only decrease in efficacy, but also become a breeding ground for bacteria, which could transfer to your face and a host of skin issues. Enter cosmetic chemist Ni’Kita Wilson, who gave us the dirt behind makeup's varying lifespans. Use Wilson’s insight as a guide for what makeup to toss and what to keep---well before it separates and dries out on you.

How long is a product's shelf life extended when it's unopened?Most skin, hair and body products can last up to 2-3 years unopened. Color cosmetics can have a shorter life span because the pigments cannot stay suspended for that length of time so I would give them up to 1 1/2-2 years.

How can you extend a product’s lifespan?Store in a cool dry place away from direct sunlight. This can help the products make it to their three year life span (if they were formulated for a three year shelf life)

How often should you wash makeup brushes?I would wash brushes weekly if you use them daily, and monthly if you use them weekly.

In addition to age, what signs indicate a product should be thrown out?It's time to toss your products if the texture has changed, you see signs of separation, the odor shifts to a funky note, or the color dramatically changes.

How long does makeup last? Follow Wilson's definitive guide:Mascara: I keep mascaras for up to a year, but I don’t use the same mascara every day, and make sure it's stored in a dry place. If you’re not careful about storage, then I would toss in 6-9 months. Why? They can dry out!

Concealer: 12-18 months. Again, if you use your fingers, wash your hands thoroughly first. Clean and/or change your sponges often. Why? The color may shift. They are not going to be stable forever!

Lip Gloss/Lipstick: 18-24 months or until the smell and/or odor changes. Why? I’m not as concerned about bacteria as I am about the oils going rancid.

Hair Brushes: Can last for years with proper maintenance.

Sunscreen: Again, if properly stored they can last up to a year after opening. Why? The sunscreen actives are not going to be the issue—I’m concerned about emulsion stability. If it is the continuous spray, then I would go by the expiration date on the package, or two years (whichever is shorter). The product may not be as effective if kept beyond the expiration date.

Facial Moisturizer/Face Masks: If in a jar, I would toss after 6-9 months. I would give it up to 12 months in a pump because it isn’t exposed to the elements. Why? The emulsion may become unstable if not stored properly—you wouldn’t want to use it! But if it is an AHA cream with a low pH and loses water, then it becomes more concentrated and could cause irritation.

Eyeliner: Liquid up to 12 months (if it isn’t dried out). Why? Since you are so close to the eye, you don’t want to take a chance with bacteria.

Lip Pencil/Lip Liner: I would keep it until it’s done, cleaning the tip occasionally with alcohol to kill any bacteria if sharing (which is not a good idea)!

Nail Polish: Expect up to 12 months with proper storage. Start examining it after 9 months to see if color is fading, or if the pigment is settling. Why? Color and application properties of the product are compromised.

Self Tanner: If in a jar, I would toss after 6-9 months. I would give it up to 12 months in a pump because it isn’t exposed to the elements. Why? If water evaporates then the DHA will become concentrated and the color may not be the same as it was when first purchased. The bigger and most probable risk is degradation of the DHA. The self tan effect may not last as long, or be as intense as when first purchased.

Hair products: Up 24 months or until you see the product separating. Why? The ingredients used are relatively stable, and typically very potent preservatives are used because of the nature of the product.