Before you start using it

Do you always have to start two nights a week?

No. There is no universal initial frequency for all active ingredients. Retinoids and potentially irritating exfoliants usually require a more gradual introduction; a moisturizer is not necessarily introduced the same way. Follow the product's guidelines and adjust according to tolerance.

Patch test: useful, but limited

Testing a small amount on a limited area can detect some reactions before widespread use, but a negative home test does not guarantee that irritation or allergy will never appear and does not replace dermatological testing when indicated.

Don't call every reaction a "purge"

Some treatments that modify cell turnover may initially coincide with changes in acne, but a breakout after starting a new product does not in itself prove that it is a "purge."

Tolerance and efficacy have different timelines

An adverse reaction can appear early. The results of many treatments require weeks or months. Don't increase the frequency just because "it's time": do it when your routine allows and your skin tolerates it.

When to seek help

Significant swelling, blisters, intense pain, extensive involvement, or concerning symptoms require medical evaluation. Difficulty breathing is an emergency.