We all want the best for our skin but when we get caught up in using a ton of different products, we may end up doing more harm than good. Always read labels and consult a dermatologist if you’re unsure about what creams and serums can be used simultaneously. In the mean time, take a look at the list below to learn about ingredients you should avoid mixing:

Retinol and Benzoyl Peroxide: These two are often prescribed to fight acne, and the former is a known anti-wrinkle ingredient. Both are also seriously powerful stuff – they can be extremely harsh on skin and drying individually, so you can imagine what combining them might do. Excessive peeling, redness and even scarring can occur, plus using the two simultaneously may actually counteract both ingredients’ effectiveness.

Copper Peptides and Vitamin C: Vitamin C is known for its ability to fight wrinkles, reduce hyperpigmentation, protect against photoaging and stimulate collagen. And copper peptides have been hailed as an even better collagen stimulator than vitamin C. But there is a persistent rumour that combining the two together may not always work. According to various beauty websites, copper peptides break down vitamin C, negating its effects and causing it to become inactive. However, my research suggestes the combining copper peptides and vitamin C is not an issue. There is evidence that the two substances would interact by vitamin C replacing the peptide as the chelating agent around the copper centre, but it is a very uncommon occurrence. Although it would somewhat depend on the relative concentrations of the two substances, the effect in an overall product would be near negligible. So while there is a shred of truth to the rumours about combining the two, it's largely overblown. 

Retinoids and Glycolic Acid:  AHAs, like glycolic acid (which is an extremely effective exfoliator), can make retinoids inactive. Definitely consider using one in the morning and one in the evening.

Sodium Benzoate and Vitamin C: When mixed with any Vitamin C ingredient, benzene can be created, and it is known that heat, light and shelf life can also affect the rate at which benzene is formed, according to Wikipedia. Benzene is considered a high hazard ingredient by the Cosmetics Database and is a known human carcinogen.

Now, what about physically combining products – like sunscreen with moisturizer or foundation, for example? Yes, it’s nice getting two steps out of the way at once, and you won’t have to deal with the potential chalkiness or greasiness that often accompanies wearing sunscreen on its own. But there’s a good chance that you’re diluting your sunscreen and affecting its photostability. Plus, sunscreen is formulated with certain ingredients for a reason, and if they interact with your moisturizer’s components, they might be rendered ineffective.