•Clean the area of skin where you will apply the product with your usual cleanser and pat it dry
•Apply half a pea size of your product right in front of your ear.
•Monitor this area of skin for 24 hours, and if you notice any sign of an adverse reaction (like redness, itching, or irritation) during this period, wash the area with a gentle cleanser and apply a skin protecting ingredient (opt for a fragrance-free cream or lotion, as these are less likely to irritate the skin, per the American Academy of Dermatology Association).
•If your skin looks A-OK, then you're good to go.
•If your only symptom is a little bit of redness, and you're still eager to try the product, Zeichner recommends a second round of patch testing. The next time around, he suggests, layer it with moisturizer "to see if it's better tolerated that way."
•If this isn't your first time developing a rash and you're having difficulty pinpointing why, it may be time to consult your dermatologist. They may deem it necessary to set up a professional patch test to identify what outside factor is causing the reaction.