The short answer
Pure vitamin C (ascorbic acid) is already temperamental: light, air, and oxidisers shorten its useful life. Benzoyl peroxide is an oxidising acne active. Put them in the same leave-on stack and you risk spending antioxidant on the peroxide instead of on your skin, plus extra dryness.
That is why both ingredient entries list each other under do-not-layer. Morning vitamin C under sunscreen still makes sense — just do not paint benzoyl peroxide over it in the same routine step.
If acne treatment is the priority that month, a morning BPO routine with evening barrier care can wait on vitamin C. Tone work from ascorbic acid is a multi-week project; it survives a pause better than an irritated barrier does.
Honest cosmetic-use guidance for home routines. Stop and seek a professional if you get swelling, blistering, or symptoms that worry you.
How to use both without stacking them
- Vitamin C mornings: cleanse → ascorbic acid or derivative → moisturiser if needed → sunscreen. No benzoyl peroxide in that stack.
- Acne mornings: benzoyl peroxide → moisturiser → sunscreen. Save vitamin C for peroxide-free days.
- Evening is a natural home for benzoyl peroxide if you want vitamin C every morning — still moisturise and watch for dryness.
- Throw oxidised vitamin C (deep orange/brown). Pairing it with BPO will not revive it.
