Give most products at least two to four weeks of consistent use before judging them, and give treatment products like retinoids eight to twelve weeks, since their benefits ride on skin cell turnover cycles that cannot be rushed. Judge on the schedule of the product's mechanism, not on the first week.
What should you track during a product trial?
Keep it simple: a weekly photo in the same light, and a short note on irritation, breakouts, and the one change you hoped to see. Memory rewrites skin history within days, so the photo record is what separates a fair trial from a vibe.
When should you stop a trial early?
Stop immediately for burning that persists, hives, swelling, or a spreading rash, and stop any product that is still causing new irritation after two weeks of reduced frequency. A trial is an experiment with a stop rule, not a commitment to finish the bottle.