I've Been A Cosmetic Chemist For 20+ Years & I Would *Never* Do This To My Skin

As beauty shoppers continue to demand ingredient transparency, more and more brands deliver: Now, you no longer have to have a degree in chemistry just to read a standard INCI list. But that doesn't make chatting with cosmetic chemists any less exciting—as a self-proclaimed ingredient fanatic, I personally find it fascinating to nerd out on all the up-and-coming science, technologies, and industry trends. (I'm not alone: A quick search on TikTok, and you'll find a smattering of lab-coat-clad individuals whipping up new potions, with 88 million views and counting.)

"Cocktailing is the layering of active ingredients one on top of the next," says Robinson. When it comes to smart skin care, more is not necessarily better—in fact, layering active on top of active can do way more harm than good in the long run. Not only can introducing multiple layers at once (glycolic acid, lactic acid, vitamin C, retinoids, etc.) lead to irritation, but it may even render them all ineffective. Not to mention, "layering too many active ingredients, like acids and retinoids, can damage your skin's moisture barrier," says Robinson, which can make your skin more prone to inflammation, dryness, and accelerated aging.

That being said, Robinson champions a simple, no-fuss routine. He recommends opting for beloved tried-and-true ingredients like vitamin C and lactic acid (use vitamin C in the a.m. and the AHA in the evening), but if you're looking for a relatively buzzy player to add to the rotation, he also praises N-acetylglucosamine (NAG), "a natural skin exfoliant [that] works to improve the skin's own exfoliation action leaving skin fresher and brighter."

Look, knowing when to toss your skin care can be tricky, especially if you have a pricey cream or serum you absolutely adore and just can't bear to part ways. But take it from Robinson: You do not want to be slathering on rancid skin care. While each product may have its own must-toss date (usually a number followed by the letter "M," meaning the number of months), he advises against using formulas more than a year old, across the board.

"I would never use a product that was older than one year old, especially if it's packaged in a jar (jars can easily become contaminated if left unopened or unwashed fingers dipping in) and/or meant to be used around the eye area," he explains, since the eye area is one of the most sensitive regions on your face.