Raise your hand if you’ve ever worried that you’re not using your skincare products correctly. There is a lot of information out there and it can feel like you’re navigating a tightrope just trying to figure out when to use your Vitamin C serum and if your peptides can be applied after an exfoliant.

This comprehensive guide is designed to help you layer your skincare ingredients effectively and get to the bottom of ingredient conflicts and stability.

The Chemistry of Skincare

Before we get into which products go well together and which should be used separately, it’s important to understand that all of this comes down to science.

Chemistry is a branch of science that deals with matter. It looks at the structure and behavior of matter as well as its properties. Chemical reactions involve the interaction of these substances and the process of converting reactants into products. Cosmetic chemistry is used to formulate products as well as determine stability and efficacy.

But don’t worry, you don’t need to be a chemist to put together a skincare routine. It’s just important to understand that when we look at whether ingredients can be mixed or not, it’s a chemistry question. There needs to be a chemical reaction to explain why one ingredient is degraded by another - and ideally some testing too!

When we focus on what is supported by science, mixing ingredients suddenly feels a lot less intimidating.

Ingredient Conflicts

An ingredient conflict just means that you may not want to combine products with certain ingredients due to a potential conflict. There can be a few potential reasons: 

• Irritation. Some products containing exfoliants, retinoids, or acne medications can cause dryness and irritation with regular use. These side effects become more pronounced when we combine more than one of these products.
• Interactions. There are some ingredients that just don’t get along and shouldn’t come in contact with each other as one or both ingredients can be degraded. And there’s some ingredients that need certain conditions, like some retinoids aren’t the most stable in sunlight.
• Formulation Stability.  When formulators are coming up with skincare brands, they need to be very mindful of how to keep the product stable long term. Peptides need a specific pH range or a certain preservative may work best in products that have more water. By the time you receive your product, this has been taken care of for you.

Irritation will depend on the products in question and your individual skin. As long as you go slow and listen to your skin, it’s perfectly fine to see what works for you in this regard. And when it comes to formulation stability, that’s nothing you need to worry about either - any reputable brand will utilize knowledgeable formulators and stability testing to ensure the final product is shelf stable. That means that the only item on the list you need to worry about is not layering skincare with ingredients that could degrade each other. And there’s not as many as you might think.

Stability Considerations

There is a lot of confusion around which ingredients don’t play well together and which are fine to combine. A lot of the information circulating online seems to stem from the recommendations given by raw ingredient suppliers when these are specifically for use when formulating. Brands have to ensure products are shelf stable for months to even years and this means they are looking at long term changes to ingredients. This does not apply to the consumer layering two separate products in their routine together unless they can rapidly degrade each other.

We are constantly being bombarded with new advice on how to order our skincare routine and it can feel like every ingredient is rendered ineffective by another. In order to cut through some of the confusion and narrow it down to just what we actually should be careful with, we’ve put together a checklist that you can use as a reminder of how few conflicts there actually are.

Required Conditions for Stability Conflicts:

This checklist allows us to assess ingredients and determine if there’s a chemical reaction that can explain the degradation of one or both ingredients, if the reaction is occurring quickly enough to have any relevance to layering separate products on the skin, and then some testing to support this is always ideal.

Example: Peptides. 

Peptides can undergo a type of chemical reaction called hydrolysis in acidic environments. For this reason, raw ingredient suppliers often suggest formulating peptide products at a slightly higher pH range. But sometimes you’ll see people assume this applies to layering peptides after chemical exfoliants and ascorbic acid too - which is not the case. Various peptides have been tested and they undergo hydrolysis too slowly for them to be broken down while you’re applying skincare.

Mixing Do's and Dont's

Still confused? Don’t worry, here’s a list that you can save and refer back to if you’re ever unsure.

DON’T COMBINE

Benzoyl Peroxide with some retinoids, hydroquinone, and unstable antioxidants.

Benzoyl peroxide is an oxidizing agent that releases oxygen as it decomposes, causing it to oxidize ascorbic acid and antioxidants that are less stable. Hydroquinone can also become oxidized3 and cause skin staining while some retinoid formulas like tretinoin cream or non-encapsulated retinol are best used elsewhere1.

Ascorbic acid with copper tripeptide-1.

This one is more of a precaution. Some copper peptide formulas appear to contain free copper which can be reduced by chelating agents like ascorbic acid, potentially oxidizing it in the process. It also looks like the copper could be separated from the tripeptide by ascorbic acid temporarily but the complex should reform again after. It would just be nice to know more until we outright say this one is fine to combine. 

Did you know: Stratia’s Interface contains a copper peptide but unlike the original copper tripeptide-1, it uses a copper salt. This - and the encapsulation - means you can use Interface with your ascorbic acid. Vitamin C derivatives are also fine to combine.

COMBINE CAREFULLY (potentially irritating)

DO COMBINE

Antioxidants with other antioxidants.

Antioxidants work synergistically together, meaning they offer higher protection used together than when used separately. Water soluble antioxidants also protect the cytosol of cells where fat soluble ones protect the cell membrane, allowing them to offer protection in different parts of our skin.

Antioxidants with sunscreen.

No sunscreen protects 100% and antioxidants used underneath sunscreen may help with photoprotection2. Sunscreens well protect against damage from UV radiation where antioxidants can go in and mop up damage from other environmental stressors.

Retinoids and niacinamide.

Niacinamide is anti-inflammatory and what we call a “ceramide promoter,” improving barrier function by increasing the production of the skin’s barrier lipids. It can help your skin better tolerate retinoids.

Retinoids and pigment inhibitors.

Dealing with dark spots? Retinoids can help compact the skin barrier so pigment inhibitors like arbutin can better penetrate. They also better distribute pigment in the skin so too don’t have areas where you’ve got more melanin clumped together.

REMEMBER THIS: all Stratia Skin products are fine to use together, provided your skin can tolerate them. They also already contain ingredient combinations that work well together, like the n-acetyl glucosamine and niacinamide in the Rewind Serum. So if you’re ever feeling overwhelmed, keep it simple.

References 

Mira is a skincare educator, blogger, and the content creator behind Skin Science by Mira and The Skincare Forum on Facebook. While skincare keeps her busy, she’s also pursuing her degree in Nursing and loves to spend her free time hiking.  As a content writer for Stratia Skin, Mira shares her evidence-based approach to skincare topics and a passion for making science accessible.