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.
The goal is to mimic what your actual usage would be like, Dr. King notes. Repeat for one week, monitoring for signs of a reaction (more on what that looks like in a second). “Sometimes these reactions can be a bit delayed, and it takes both multiple exposures and/or a prolonged amount of time before they show up,” she explains. “If you make it through the week with no issues, that’s a pretty good sign that you should be okay applying that product to your face.” (For context, the American Academy of Dermatology recommends a similar method.)
The targeted approach
Though Dr. Palm also recommends the forearm method for body care, she says it can be helpful to try products on the area where they’ll actually be used: “Facial products should be tested on facial skin and can be patch tested behind your ear. Body care should be tested on the body and can be patch tested on the inner forearm.”
If you want extra assurance that your face isn’t going to freak out from a new product (which might be the case if that nightmare has happened to you in the past), testing behind your ear is a good idea. Dr. Palm adds that, for most people, applying the product only once and leaving it on for 12 to 24 hours is a sufficient amount of time to check for a reaction. However, if you’ve suffered from reactions in the past, she says that testing a product in the same area for several days in a row is smart in order to mitigate the possibility of a delayed issue.
The bandage test
Dr. Henry offers yet another method of at-home patch testing: Apply a nickel-size amount of the product to clean, dry skin on the inner forearm, then cover it with a bandage for 48 hours (try not to get it wet during this time; you don’t want to wash off or dilute it). Sealing up the product in this way allows for more absorption of potential allergens, she explains. If you don’t mind sporting a bandage for a couple days, you may end up seeing if there’s a reaction faster; and if you don’t, you can feel fairly confident that you can apply it on your face without issue, Dr. Henry says.
No matter which test you go with, if you experience any negative symptoms during the testing period, you should wash off the product immediately, according to all three doctors. To that point….
What symptoms should you look for when patch testing skin care products?
According to Dr. Palm, you should look out for signs of inflammation like skin discoloration, itchiness, bumps, swelling, welts, and scaling. Just keep in mind that these issues can show up slightly differently on different skin tones. “In darker skin, you may not see redness in the classic sense, as you would on lighter skin, but you’ll still see some changes in tone. The skin may even look a bit purple,” Dr. Henry says. Textural changes, such as little bumps and itchiness, are universal across all skin types, so keep an eye out for those, both of which will let you know that your skin is unhappy, she adds. (These reactions tend to manifest as some combination of the above symptoms, rather than a single one, Dr. King says.)
If your skin starts to react, abort the testing process immediately. Wash the affected area thoroughly with a gentle cleanser and consider applying an anti-itch cream, such as over the counter 1% hydrocortisone cream, to soothe the area, Dr. Palm adivses. If the symptoms haven’t improved after three to four days, call your primary care doctor or a dermatologist, if you have one, Dr. Henry adds.
What comes next?
At the risk of eliciting an audible duh: If your skin “fails” a patch test, that product should be a no-go for you. If everything looks and feels fine, you can go ahead and start working the product into your routine, though it’s always a good idea to incorporate formulas that contain active ingredients gradually, as SELF previously reported.
Also important: If you regularly experience reactions to new skin care products, consider making an appointment with a dermatologist, if you’re able to. (A primary care doctor can give you a referral if you need one.) With at-home patch testing, you can’t differentiate whether you’re experiencing allergic contact dermatitis or irritant contact dermatitis because the symptoms are so similar, Dr. Henry explains. (The former involves an immunological response, the latter does not.) Plus testing a product at home won’t tell you exactly which ingredient in that product is the culprit. “You want to find out which specific ingredients are problematic for you so that you can truly avoid them, and an in-office patch test is the best way to do that,” Dr. Henry says. If you decide to go that route, she advises bringing in any products that you’ve self-tested in the past (both with positive and negative results), as they can provide your dermatologist with a helpful frame of reference.
At the end of the day, figuring out what’s irritating your skin can require quite a bit of detective work. At-home patch testing is a good place to start your sleuthing—and can mitigate the likelihood of ending up with an uncomfortable and unsightly reaction—but in-office patch testing is the best way to put all of the puzzle pieces together. Your skin is worth the extra effort!
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