Lactic Acid (AHA) + Tretinoin: not the same night
Both are real, useful actives on their own. Layered together, or used the same night, they're more likely to irritate skin or destabilize each other than to work better. The fix isn't dropping one — it's alternating them.
Why they conflict
Both speed up skin cell turnover and thin the outer skin layer. Used together, the combined exfoliation and increased sun sensitivity go well past what either ingredient produces alone — this is the most common cause of a "retinol burn."
The schedule that works
Both skip Sunday. This is the same staggering Skinzy's own routine builder applies automatically when a scan recommends two conflicting actives — see each ingredient's own page for its full introduction schedule.
If you're introducing both for the first time, start with Lactic Acid (AHA) alone for a week or two before adding the other — it has the gentler safety rating of the two, so if skin reacts, there's only one new variable to trace it back to.
Want both effects without the conflict?
Rather than staggering these two, either one has real alternatives that work alongside it without the same-night restriction.
Questions people ask
Not in the same application. Alternate nights instead: Lactic Acid (AHA) on Monday/Wednesday/Friday, Tretinoin on Tuesday/Thursday/Saturday, both skipping Sunday.
Both speed up skin cell turnover and thin the outer skin layer. Used together, the combined exfoliation and increased sun sensitivity go well past what either ingredient produces alone — this is the most common cause of a "retinol burn."