Patch Testing New Skin-Care Products: A Step-by-Step Guide
How to test a new topical product on a small area before using it more widely -- the AAD method, in order.
The American Academy of Dermatology estimates that more than 15,000 substances can cause an allergic skin reaction. A patch test is a small, contained way to find out whether a new product -- a botanical remedy, a moisturizer, anything applied to skin -- is one of them, before applying it to a larger area or an already-irritated patch of skin.
When this matters most
Patch testing matters most before trying a new topical botanical (especially anything in the Asteraceae/daisy family, which carries a higher cross-reaction rate), before applying anything to skin that is already irritated or broken, and for anyone with a known history of skin allergies or eczema.
The AAD method, step by step
Choose a small area unlikely to be accidentally washed or rubbed off -- the inside of the forearm or the bend of the elbow works well. Apply a quarter-sized amount of the product as thickly as you would use it normally. Leave it on for as long as you would normally leave it on -- for a rinse-off product like a cleanser, that means leaving it about 5 minutes before rinsing just that spot; for a leave-on product like a lotion or a homemade botanical preparation, leave it in place.
When to stop and what it means
Stop immediately and wash the area if you notice redness, itching, swelling, stinging, or blistering during the test. A reaction on a small patch test area is a reasonable predictor that a larger application would cause a larger reaction -- don't proceed with the product. A significant or painful reaction is worth mentioning to a clinician, particularly if you plan to try other products in the same category.