Lumiere
The four verdicts
| Verdict | What it means |
|---|---|
| Fine together | Layer them in the same routine. No meaningful conflict. |
| Caution | Not harmful, but the combination adds little and costs irritation. Usually better split. |
| Separate | Use one in the morning and one at night, or on alternate days. |
| Keep apart | One degrades the other, or the combined irritation is reliably too much. |
The principle behind all of it
Very few skincare combinations are chemically forbidden. What limits you is an irritation budget: your barrier tolerates a certain amount of active pressure per week, and over-spending it means nothing works, because a damaged barrier can't make use of anything you apply.
That's why "separate" and "alternate" appear more often here than "never". The ingredients aren't the problem. The schedule is. There's a longer treatment of this in the layering guide.
Order within one routine
Thinnest to thickest, water-based before oil-based: cleanser → toner or essence → water-based serum → treatment → eye cream → moisturiser → oil (PM) or sunscreen (AM). Sunscreen is always last.
Frequently asked questions
Which skincare ingredients should not be mixed?
Genuinely few. The pairings worth separating are retinoids with AHA or BHA exfoliants, benzoyl peroxide with tretinoin or retinol (adapalene is stable with BPO), benzoyl peroxide with vitamin C, and strong acids with peptides. Most other combinations are a question of how much total irritation your skin can absorb in a week, not of chemistry.
Can I use vitamin C and niacinamide together?
Yes. The claim that they neutralise each other traces to 1960s research on heated, unbuffered solutions and doesn't apply to modern cosmetic formulations. Commercial products combine them routinely.
Is this checker medical advice?
No. It's general guidance about cosmetic ingredient compatibility. It doesn't account for prescription medication, pregnancy, or a diagnosed skin condition — speak to a dermatologist or pharmacist for those.
What does 'alternate nights' actually mean?
Use one active on one night and the other on a different night, rather than layering both in the same session. A typical pattern is retinoid on Monday, Wednesday and Friday, exfoliating acid on Tuesday and Saturday, and nothing active on the remaining nights.
This tool gives general cosmetic-ingredient guidance, not medical advice. It doesn't account for prescription treatments, pregnancy or diagnosed skin conditions.