Patch test

A patch test is a precautionary trial used to detect contact allergies or sensitivities before a product is applied to the face or a larger skin area. A small amount of the product is applied to an inconspicuous site — typically the inner forearm or behind the ear — and left for 24 to 48 hours without washing. If redness, itching, swelling, or blistering occurs, the product should not be used. Patch testing is especially recommended before using high-concentration actives (retinoids, AHAs, vitamin C), products containing fragrance or essential oils, and anything applied to compromised skin. It does not replace a clinical patch test conducted by a dermatologist to diagnose specific contact allergens.

• Non-comedogenic A label claim indicating a product is formulated not to clog pores.
• Comedogenic Describing an ingredient or product with the potential to clog pores and cause blackheads or whiteheads.