Patch Testing

What It Is

The practice of applying a new skincare product to a small, discreet area of skin (inner arm, behind the ear, or jaw) for 24–48 hours before full-face application, to assess for allergic contact dermatitis or irritant reactions. Distinct from clinical patch testing done by dermatologists to diagnose specific allergen sensitivities. Any new active ingredient — particularly fragrance, essential oils, strong actives (AHAs, retinoids, Vitamin C) — should be patch tested before first use.

Key Context

A positive patch test (redness, itching, swelling, rash) indicates either an irritant reaction (from potent actives) or an allergic contact reaction (from a specific allergen). Distinguish by removing the product: irritant reactions resolve quickly; allergic contact dermatitis may persist and spread.

Learn More

• Sensitive Skin Routine
• Ingredient Combinations to Avoid