Since vitamin C is such a powerful skincare ingredient, you often shouldn’t mix a serum with a high concentration of this vitamin with other products containing powerful active ingredients. Some ingredients will actually counteract the effects of vitamin C, while others will just increase your risk of irritation. When you apply a vitamin C serum, you should avoid applying products with AHAs or BHAs (like glycolic acid, lactic acid, and salicylic acid), retinol, or benzoyl peroxide. If you use products with these ingredients in your routine, simply apply them at different times. For example, apply a vitamin C serum in the morning, and retinol at night.