A true statement about patch testing is that it is a test for allergies conducted prior to using a product; typically how long before service?

• A. Immediately before service
• B. 24-48 hours before service
• C. One week after service
• D. Only after an adverse reaction

Answer: (B)

Patch testing is a pre-service allergy check. Since many cosmetic allergies are delayed and show up within 24 to 48 hours, scheduling the test 24–48 hours before the appointment gives time to observe any reaction and adjust product choices if needed. Doing it immediately before service wouldn’t reveal whether a reaction will occur during or after application, and waiting a week after service wouldn’t help prevent an adverse event. So, the standard lead time is about one to two days before the service.