The Complete Guide to Skincare Ingredient Conflicts
Build your perfect routine in the app
Pre-loaded with The Ordinary products. Auto-sorts your routine. Flags conflicts in real time.
Building a multi-step skincare routine involves a lot of ingredients — and some of them genuinely don't work together. Using incompatible actives in the same session can either neutralise their benefits, irritate the skin, or in some cases cause a chemical reaction that actually damages the active ingredients themselves.
This is a comprehensive reference guide covering every major conflict pairing you need to know about: what the conflict is, why it exists, and what to do instead.
Why ingredient conflicts matter
Skincare actives are precise. They work within specific pH windows, they compete for the same receptors, and some react chemically when they meet on the skin. The consequences of getting this wrong range from wasted product to barrier damage, redness, and sustained irritation.
The good news: there are actually only a small number of conflict pairs that genuinely matter. If you learn these, you have covered the vast majority of real-world mistakes.
The major conflicts, explained
1. Retinoids vs. Direct Acids
Always keep separate.
Retinoids include: Retinol 0.2% / 0.5% / 1% in Squalane, Granactive Retinoid 2% / 5% in Squalane, Granactive Retinoid 2% Emulsion.
Direct Acids include: AHA 30% + BHA 2% Peeling Solution, Glycolic Acid 7% Toning Solution, Lactic Acid 5%, Lactic Acid 10%, Mandelic Acid 10% + HA, Salicylic Acid 2% Solution, Azelaic Acid Suspension 10%.
Why they conflict: Retinoids already cause mild, controlled exfoliation by accelerating skin cell turnover. Adding a chemical exfoliant (AHA or BHA) in the same session doubles this effect. The skin's barrier becomes compromised — leading to redness, irritation, peeling, and long-term sensitivity that can persist for weeks.
What to do: Alternate. Use acids on some nights, your retinoid on others. A common pattern is acids Tuesday and Friday; retinoid Monday, Wednesday, and Saturday. Never both in the same session.
2. Retinoids vs. Copper Peptides
Always keep separate.
Copper Peptide products include: Buffet + Copper Peptides 1%, and any NIOD or third-party copper peptide formula.
Why they conflict: Copper Peptides work by delivering copper ions to the skin to support wound healing and collagen synthesis. Retinoids are already aggressive agents that encourage cell turnover. Used together, the combination can cause irritation and may interfere with the beneficial activity of both actives.
What to do: Keep Copper Peptides on non-retinoid nights. They can also be used in the AM while retinoids remain in the PM.
3. Pure Vitamin C vs. Niacinamide
Best kept separate.
Pure Vitamin C products: 100% L-Ascorbic Acid Powder, Vitamin C Suspension 23% + HA Spheres 2%, Vitamin C Suspension 30% in Silicone.
Why they conflict: L-Ascorbic Acid is highly acidic (pH ~2.5–3.5). Niacinamide at this pH can convert into nicotinic acid, which is a vasodilator that causes facial flushing. The conversion also means neither ingredient performs as well as it would alone.
What to do: Niacinamide in the AM; pure Vitamin C in the PM. If using a Vitamin C derivative (Ascorbyl Glucoside, MAP, Ascorbyl Tetraisopalmitate), the conflict is significantly reduced — but separation is still a good practice.
4. Pure Vitamin C vs. Peptides
Always keep separate.
Peptide products include: "Buffet", Argireline Solution 10%, "Buffet" + Copper Peptides 1%, NIOD CAIL Copper Amino Isolate Lipid, and other peptide-forward serums.
Why they conflict: L-Ascorbic Acid creates a highly acidic environment that degrades the activity of peptides. Peptides are chains of amino acids that work in a near-neutral pH environment. The strong acidity of pure Vitamin C disrupts the peptide bonds, reducing or eliminating their effectiveness.
What to do: Keep peptides in your AM routine (or use them in the PM on non-Vitamin C nights). Use pure Vitamin C in the PM without peptides.
5. Pure Vitamin C vs. EUK 134
Strict — always keep separate.
Why they conflict: EUK 134 0.1% is a synthetic superoxide dismutase mimic — a powerful antioxidant enzyme catalyst. Being an enzyme, it is structurally sensitive to extreme pH. The strong acidity of L-Ascorbic Acid doesn't just reduce EUK 134's effectiveness — it actively destroys the molecule, rendering it completely inert.
What to do: EUK 134 in the AM; pure Vitamin C in the PM. This is one of the strictest conflicts in The Ordinary's range. There is no safe overlap.
6. Copper Peptides vs. Vitamin C (any form)
Always keep separate.
Why they conflict: Vitamin C — in both pure and derivative forms — can interfere with the copper complex in Copper Peptide products. Copper Peptides require an intact copper ion to function; oxidative ingredients or high-acid environments can disrupt this.
What to do: Keep Copper Peptide products on separate days or in the AM while Vitamin C is in the PM.
7. Copper Peptides vs. Direct Acids
Always keep separate.
Why they conflict: Direct acids (AHAs and BHAs) create the highly acidic pH environment that disrupts copper peptide chemistry. Acids can strip the copper ions from the peptide complex, reducing or eliminating their activity.
What to do: Use acids and Copper Peptides on alternate nights.
8. Retinoids vs. Pure Vitamin C
Always keep separate — but for practical reasons, not because of a direct chemical conflict.
Why they conflict: Both ingredients are used in the PM, both increase skin sensitivity, and both can irritate when overused. Using them together significantly raises the risk of over-sensitisation and redness.
What to do: Use Vitamin C derivatives (like Ascorbyl Glucoside) in the AM where they don't conflict with retinoids at all. If you prefer pure Vitamin C, alternate evenings.
9. Multiple retinoids in the same routine
Never stack retinoids.
Using more than one retinoid product at the same time — for example, Granactive Retinoid 2% and Retinol 0.5% in the same evening routine — is not recommended. It provides no additional benefit and significantly increases the risk of irritation, barrier damage, and retinoid dermatitis.
What to do: Use one retinoid at a time. Finish or remove one before introducing another.
10. Niacinamide vs. EUK 134
Worth separating — affects integrity, not safety.
Why they conflict: Niacinamide can affect the integrity of pure Vitamin C when used together, but the broader concern is that EUK 134 is sensitive to any environment that might interfere with its enzyme function. DECIEM recommends keeping EUK 134 in the AM separate from ingredients that may compromise its activity.
What to do: EUK 134 in the AM; Niacinamide is flexible but AM works well.
11. Resveratrol vs. EUK 134
Do not mix these two.
Resveratrol & Ferulic Acid and EUK 134 0.1% should not be combined in the same application, as they can interfere with each other's antioxidant pathways.
What to do: Use one or the other in a given session — or use one AM and one PM.
The ingredients that don't actually cause issues
It's worth noting what is often incorrectly cited as a conflict but is not:
- Niacinamide and Retinoids: Some sources say these conflict, but this is largely debunked. While high-dose nicotinic acid can cause flushing, Niacinamide and Retinol can be used in the same routine without issues for most people — though it's most natural to keep Niacinamide in the AM and retinoids in the PM anyway.
- Vitamin C and SPF: These do not conflict. In fact, Vitamin C (particularly derivatives) works synergistically with SPF as an antioxidant layer.
- Hyaluronic Acid and anything: HA is remarkably conflict-free. It layers well with virtually every other ingredient in skincare.
Conflicts and body areas
One important nuance: products only conflict if they are applied to the same area of the body. A retinoid used on your face does not conflict with an acid used on your hands. The Skincare Routine app takes this into account — body areas can be assigned to each product, and the conflict detection is scoped accordingly.
How the Skincare Routine app manages all of this
The Skincare Routine app has a built-in conflict detection system that covers every pairing described in this guide.
During your morning or evening routine, as you tick products off your usage list:
- A red checkbox appears on any remaining product that would create a hard conflict with what you've already used. Ticking it is technically possible (you can override it) but the conflict is clearly flagged.
- An orange checkbox indicates a softer warning — worth reading the reason, but not as strict.
- The reasons are shown inline, so you understand exactly why a conflict exists — not just that one does.
Custom conflicts are also supported: if there are two products you personally prefer not to use together (regardless of standard compatibility rules), you can define that directly in the app.
All 100+ pre-loaded DECIEM products have their conflict relationships pre-built. For custom products from other brands, you specify the key ingredients when adding the product, and the conflict system applies automatically based on those ingredients.
Download it at skincareroutine.app.
Quick reference: The major conflict pairs
| Ingredient A | Ingredient B | Rule |
|---|---|---|
| Retinoids | Direct Acids (AHA/BHA) | Never same session — alternate nights |
| Retinoids | Copper Peptides | Never same session |
| Retinoids | Pure Vitamin C | Separate routines |
| Pure Vitamin C | Niacinamide | Separate routines (Vit C PM, Niacinamide AM) |
| Pure Vitamin C | Peptides | Never same session |
| Pure Vitamin C | EUK 134 | Strict — never same session |
| Any Vitamin C | Copper Peptides | Never same session |
| Copper Peptides | Direct Acids | Never same session |
| Resveratrol | EUK 134 | Never same session |
| Multiple retinoids | Together | Use one at a time |
This covers the vast majority of real-world conflicts in any The Ordinary or multi-brand routine. If in doubt, the Skincare Routine app will tell you.
Ready to start your routine?
Download the Skincare Routine app — available on iOS and Android.