Knowing which skincare ingredients work well together is just as important as knowing which ones should never be combined. Using incompatible ingredients can cause irritation, reduce efficacy, or even damage your skin barrier. Here is your comprehensive guide to ingredient combinations to avoid.

Retinol and AHAs or BHAs: A Recipe for Irritation

Both retinol and exfoliating acids like glycolic acid and salicylic acid work by accelerating cell turnover. Using them together is overly aggressive and can lead to severe irritation, peeling, and a compromised skin barrier. Instead, use AHAs or BHAs in the morning and retinol at night, or alternate them on different days. If you are new to either ingredient, start by using each only once or twice per week on separate nights.

Vitamin C and Retinol: Timing Matters

While you can use both vitamin C and retinol, they should not be used at the same time. Both ingredients require a specific pH to work effectively, and their optimal pH ranges are different. Vitamin C works best at a low pH, while retinol works best at a higher pH. Using them together can render both less effective. The solution is simple: use vitamin C in the morning and retinol at night. This gives you the benefits of both without the conflict.

Benzoyl Peroxide and Retinol: Counterproductive Pairing

Benzoyl peroxide can oxidize and degrade retinol, making it less effective. If you use both for acne treatment, apply benzoyl peroxide in the morning and retinol at night. Alternatively, use a formulation that is specifically designed to be stable with both ingredients. Never layer them directly on top of each other.

AHAs or BHAs and Vitamin C: pH Conflict

Both vitamin C and AHAs or BHAs require an acidic pH to work. While they can be used in the same routine, layering them directly can cause excessive irritation and may not provide additional benefits. If you want to use both, apply your vitamin C serum first, wait fifteen minutes for it to absorb fully, then apply your AHA or BHA. Alternatively, use them in separate routines, vitamin C in the morning and acids at night.

Copper Peptides and Vitamin C: A Delicate Balance

Copper peptides and vitamin C can degrade each other when applied together. The copper ions can oxidize the vitamin C, while the acidic pH of vitamin C can affect the stability of copper peptides. To get the benefits of both, use vitamin C in the morning and copper peptides at night. Some newer formulations have stabilized both ingredients together, but it is safer to separate them.

Multiple Exfoliating Acids: More Is Not Better

Using multiple exfoliating acids at once, such as glycolic, salicylic, and lactic acid, is a common mistake. Your skin needs time to recover between exfoliation sessions. Over-exfoliating can strip the protective barrier, leading to redness, sensitivity, and breakouts. Stick to one exfoliating acid in your routine and use it no more than three times per week unless your skin is well-conditioned and used to acids.