While you could chalk all this up to the harsh truth that some products just won’t be compatible with everyone’s skin, the potential for mold is too concerning to leave unaddressed, so we dug a little deeper. 

What’s in the Kosas Revealer Concealer Formula?

After taking a look at the formula of the Kosas Revealer Concealer, cosmetic chemist Perry Romanowski tells Allure that the preservatives used in the products aren’t the most effective. Cosmetic chemist Krupa Koestline also weighed in, explaining that the strength and efficacy of these preservatives are affected by pH and electrolytes, which makes them less effective than some non-clean products on the market which are more stable. “They have chosen something which, in my view, is an inferior preservation system,” Romanowski explains. “Their preservative includes potassium sorbate, sodium benzoate, and phenethyl alcohol. Unfortunately, if this product is not formulated at a pH of below 5.0, then microbes of mold can grow.” There’s no way to know what pH level the concealer was formulated at, but Romanowski explains that above a pH of 5.0, the preservatives that Kosas formulates with don’t work as intended.

Romanowski continues, saying that it would have been better for Kosas to use a robust preservative system that includes methylparaben and propylparaben because they are particularly effective against mold and fungi and can work at a wider pH range.

How Long Is Kosas Revealer Concealer Supposed to Last?

The brand also explains on its FAQs page that every unopened Kosas product “has a shelf life of two to three years depending on whether they contain water,” which this concealer does. Each bottle also has a “product after opening symbol” that indicates the estimated amount of time a customer has to use the product after opening — for the concealer, it’s six months. 

So while the Redditor’s claim that started all this conversation ultimately can’t be written off as completely invalid, according to their own timeline, they allege that they spotted the mold three months after that “product after opening” cutoff.  It’s possible that many of the similar claims online are also a result of not reading the expiry labels, especially given the lack of context attached to them. 

It’s also important to note that any claim that an unopened product has a shelf life of two to three years, begins at the date the product is packaged. So, if that product sits in a warehouse or on a shelf for a while before being bought, it might be closer to expiration at that point. In addition to the PAO symbol, all products should have a batch code indicated somewhere on the packaging — you can use that code to determine how long ago the product was made. 

How Do You Know If Your Makeup Has Expired? 

Before you go panicking and tossing out your current tube of Revealer Concealer, there are a few keys ways to tell if it’s expired. In addition to any PAO symbols, batch codes, or expiration dates printed on the packaging, you can always use your own senses to suss out whether or not a product is still good to use.