If you regularly read skin care stories, you’ve probably come across the often-touted advice to patch test new products before trying them. (It’s certainly a suggestion SELF has made more than once!) But what exactly does patch testing a new serum or moisturizer entail? Is it something everyone really needs to do, or does it fall more into the “wash your comforter weekly” advice category—a goal that’s idealistic, but probably won’t happen every time it should?
We asked a few top dermatologists for their take on this common recommendation, as well as step-by-step instructions for how to patch test skin care products at home.
What is skin care product patch testing?
There’s no rocket (or even dermatological) science involved here: A DIY patch test simply involves applying a small amount of a new product on an inconspicuous spot—before you slather it all over your face or body—and monitoring your skin to see how it reacts. (More on all of those specifics to come.)
“It helps let you know if you’re going to experience a reaction to a new product before you’ve applied it on your face, where a reaction is much more unpleasant to deal with,” Hadley King, MD, board-certified dermatologist and clinical instructor of dermatology at the Weill Medical College of Cornell University in New York City, tells SELF. Just don’t confuse this with professional, in-office patch testing, during which a dermatologist or allergist tests specifically for reactions to potential allergens, like common skin care ingredients or environmental substances. To that point, a DIY patch test at home can help you determine if you can tolerate a particular product, but if you have a reaction, it won’t pinpoint exactly which ingredient is causing the problem, Michelle Henry, MD, board-certified dermatologist and clinical instructor of dermatology at the Weill Medical College of Cornell University in New York City, tells SELF.
Who should consider patch testing skin care products?
All of the dermatologists SELF spoke with agreed that, ideally, at-home patch testing is a good idea for everyone and every type of product that has prolonged contact with your skin, from moisturizer to makeup. However, it can admittedly be time-consuming and cumbersome. As such, they all also emphasized that patch testing is especially important for certain people. If you have a history of sensitive skin; have reacted poorly or experienced irritation after using new products in the past; have rosacea, eczema, psoriasis, or other chronic skin conditions; or have known skin allergies, at-home patch testing is particularly important, Dr. King says.
You can also decide whether or not to patch test based on the kind of product you’re trying. “Most people can get away with not patch testing mild formulas, such as fragrance-free moisturizers that don’t contain any active ingredients,” Melanie Palm, MD, a board-certified dermatologist in San Diego and a clinical professor at Scripps Encinitas Memorial Hospital, tells SELF. On the flip side, any product with a lengthy ingredients list and/or actives such as retinoids, exfoliating acids, or vitamin C, should be patch tested before you fully incorporate it into your routine, since these are more likely to elicit a reaction, Dr. Palm advises.
How to patch test a skin care product
Our experts offered up some slightly differing pieces of advice, so you have options.
The forearm method
Dr. King suggests applying a thin layer of the new product to a nickel-size area of clean, dry skin on the inside of the forearm. Why here? It’s a discreet spot, so if a reaction does show up, it won’t be super visible. Still, the skin is delicate enough that it’s comparable to the skin on your face, she explains. Leave it on and don’t wash it off, then reapply the product—the same amount in the same spot—as often as the instructions recommend, be that once or twice daily.