Dermatologists are well suited to understand cosmeceutical science and the benefits of particular cosmeceutical products – especially if they are readers of this column. However, there is another critical thought process that must be undertaken when designing an efficacious skin care regimen for patients: Topical products should be applied in a particular order to maximize efficacy. This is because cosmeceutical ingredients interact with, change each other, and are affected by temperature, pH, humidity, and the microbiome in which they are in contact. This column focuses on the factors that should be considered when recommending skin care regimens to patients and in which order to apply topical products.
The chemistry of ingredients and how they interact is well understood by personal care product formulators. I think of formulators as chefs who are using ingredients and placing them in the formulation in a well-defined order under controlled circumstances that affect the final product. For example, ceramides are used in barrier repair moisturizers. The right form of ceramide must be chosen and used with the 1:1:1 ratio of ceramides, fatty acids, and cholesterol for the product to be effective at repairing the barrier.1 However, the order of when the ceramides are added to the product formula also impacts efficacy. Waxy ceramides and cholesterol require heat to liquefy and form the proper mixture with the other ingredients. Too much heat can damage fatty acids. Also, heat can inactivate finicky active ingredients such as vitamins C and E. For this reason, the ceramides and cholesterol are often incorporated first, allowing the formula to cool before the active heat labile ingredients are added. The speed at which something is mixed can generate heat and affect the final preparations, so temperature is an important consideration at all steps in the formulation procedure.
Just as the order of creating formulations affects the final product, the order of product placement on the skin influences skin care product efficacy. If a low pH skin care product (such as a glycolic acid cleanser) is used on the skin, this is going to affect the efficacy and safety of the product that is applied next to the skin. Such a chemical phenomenon should be considered when designing the order of product applications when designing a skin care regimen, particularly when incorporating ingredients that are known to interact with other ingredients, such as benzoyl peroxide, retinoids, hydroxy acids, hydroquinone, vitamin C, and peptides.