How to Do a Skin-Care Patch Test — and Why It Matters

Some food for thought: On average, women use 12 personal care products daily, which amounts to about 168 chemical ingredients, according to the Environmental Working Group (EWG). Splurging on a new skin-care product is fun and games — until you try a product that doesn’t agree with your skin, leaving you red, itchy, or irritated.If you notice your skin is experiencing unexplained irritation after swapping in a new skin-care treatment, its ingredients may be to blame.That’s why skin-care experts and brands alike recommend a patch test before you add a new formula to your regimen.

What Is a Patch Test?

Broadly defined, a patch test is when you apply a product or ingredient to a small area of skin and observe the skin’s reaction, says Nava Greenfield, MD, a board-certified dermatologist with Schweiger Dermatology Group in New York City.Patch-testing your products will help you identify how your skin may react to a new product before you slather it all over and potentially face the consequences.What could that reaction look like? A mild reaction might be a little redness, says Joshua Zeichner, MD, the director of cosmetic and clinical research at Mount Sinai Hospital in New York City. On the more extreme end, you could end up with something he deems severe, like a “scaly itchy rash that may require a prescription medication to calm it down.”So, how do you perform an at-home test, anyway? And when should you pay a visit to the professionals instead? Here, we break down everything you need to know about skin-care patch tests with expert insight from board-certified dermatologists.

What Is a Patch Test Used For?

A patch test is used to identify whether your skin may react negatively to a product or ingredient. It will help you decide whether to proceed with incorporating that product into your skin-care regimen — or if you should avoid it entirely.“A reaction may suggest a contact allergy or sensitivity to the product or ingredient,” says Dr. Greenfield. Signs of an allergic reaction include a rash, hives, and discoloration (redness on lighter skin tones, or dark brown, purple, or gray on darker skin tones), per the U.S. Food and Drug Administration (FDA). It’s important to note that sensitivity can also yield similar-looking results.According to Dr. Zeichner, you can develop one of two types of contact dermatitis in response to a new skin-care product: irritant contact dermatitis or allergic contact dermatitis.The former causes a reaction “because you’re using a harsh ingredient” that your skin chemistry can’t withstand, he notes. On the other hand, he explains, allergic contact dermatitis is when “an ingredient in the product elicits an immune response.”A professional patch test can pinpoint allergens, while a less-comprehensive at-home test can give you an idea of what you might be allergic to. But more on that ahead.

At-Home Patch Testing or In-Office: What’s the Difference?

You can patch test in one of two ways: in a dermatology office or at home. But they’re vastly different experiences.

The primary difference between at-home patch testing and professional patch testing is that the DIY version “can determine if you’re sensitive to a product, but it doesn’t necessarily tell you if it’s an allergy or an irritation,” says Zeichner.

“It also doesn’t tell you what ingredient you are specifically reacting to,” he continues. “If you’re using a product with a harsh active ingredient, you can likely attribute the reaction to that active ingredient” — but it’s not definitive.

Professional patch testing is a whole different ball game. “It’s a procedure in which upwards of 80 adhesive patches or more are applied to a patient’s back,” says Zeichner. “Each patch contains a single active that is commonly associated with an allergic reaction in the skin, such as fragrances, dyes, and preservatives.

“These patches are left in place for 48 hours — so that means no shower while they’re on,” he continues. “Then you come back to the office and your dermatologist removes them and evaluates your skin to see whether you’re developing a reaction.”

The verdict? An at-home patch test when you purchase new skin-care is a good standard practice to prevent an avoidable reaction. But you’ll still need a professional procedure for suspected cases of allergic contact dermatitis.

What Products Should You Patch Test?

Annoying as it may seem, you should patch-test every new skin-care product before implementing it into your routine, says Zeichner.

Feeling impatient? At the very least, do a patch test before trying formulas containing active ingredients, he advises, noting that exfoliating acids, vitamin C, and retinol are the three most potentially irritating ingredients.

As far as what you can likely get away with not patch testing, the pro says mild moisturizers (formulas that are free of fragrance and active ingredients) “should be just fine.”

The takeaway? It’s best practice to patch test all your products, especially those with harsh active ingredients. After all, you and your skin are better safe than sorry.

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