Cosmetic ingredients mixed together can either enhance or negate each others' effects.
Cosmetic chemistry describes the interaction between various ingredients in one product as synergistic or antagonistic. Synergy means that ingredients mutually enhance their properties achieving a combined effect that is stronger than a mere sum of their separate effects. Inversely, antagonists reduce each other’s activity, in some cases even cancelling each other out (mutual inactivation or a complete levelling out of effect). T
he substances themselves do not necessarily alter their structures, this is about their impact on the skin. Mutually enhancing effect is demonstrated, for example, by some AHAs. You may have noticed that oily and problem skin cosmetic products often contain several different alpha hydroxy acids — that’s because they’re more effective in complex. Glycolic acid is often combined with citric or pyruvic acid. Salicylic acid makes a good combination with glycolic acid and an antibacterial agent, benzoyl peroxide.
Peptides can mutually enhance each others' effect.
For example, Argireline, Leuphasyl and Syn-Ake together smooth out wrinkles more effectively than you would expect based on the research of their effects separately. The most stand-out example of synergy in cosmetic ingredients is antioxidants.
The thing is, when an antioxidant captures a free radical, it transforms and often becomes a free radical itself. Then this free radical is captured by the next antioxidant, then the next and the next, and that is why antioxidant cocktails with many antioxidant ingredients are more effective.
Vitamin C, for instance, will be more effective combined with vitamin E and green tea extract, then on its own. Same goes for aloe vera extract combined with blueberry, lemon and orange extracts. Generally it would be correct to say that antioxidant activity grows with the increase of antioxidant components in a product.
Antagonists in their turn can cancel each other out. For example, alpha hydroxy acids easily disarm peptides — a product containing both would be less effective than a product with just one group of ingredients. Retinol and its derivatives negate the effect of prebiotics, so in acne treatment it is wise to choose either retinol-based therapy or prebiotic.
Curiously, the activity of physical sun filters, such as titanium dioxide or zinc, decreases in the presence of natural oil, while mineral oil on the contrary makes them more effective. So when you’re on the beach, do not apply sunscreen and natural oils at the same time, and if you wish to protect your skin from drying opt for mineral oil instead. If you’re using the same brand products, most likely they’ll have synergistic effect as cosmetic developers usually assume that customers will apply several products of the same line and create synergistic formulations.
At the very least one can expect not to have antagonistic ingredients in the products of the same line. Remember, however, that one cosmetic brand can have several lines or ranges aimed at different skin problems. The combination of a cleansing product for oily skin with a concentrate for mature skin isn’t necessarily the best!
When you use products of different brands, there is always a risk of ingredient antagonism.
And even though antagonists may not cancel each other out entirely if they’re applied in different forms, there’s always a definite possibility. So if your new serum or cream seem somewhat disappointing, try to stop using other brands’ products for a bit and apply the ones that are recommended for combined application, at least for a few days as samples, before you issue an ultimate verdict. Sometimes, unexpected synergy is worse than antagonism.
Side effects often occur when people try to use a bunch of retinol-based products for ageing skin or for oily skin. Each product would be safe and effective on its own, but their combination may prove dangerous and lead to skin irritation, flaking and even inflammation. Essential oils require extreme caution as well.
Creating a complete list of antagonists and synergists would probably be impossible.
When we talk about ingredient combination, most often we mean 1+1, but cosmetic products often contain dozens of active ingredients. And in every case cosmetic developers test the interaction of all components, their mutual preservation, the stability of the product, its effect on the skin and compatibility with other products of the same line. The same agent can be synergistic in one formulation and antagonist in the other. Cosmetic development is an art as much as science. Some combinations have passed the test of time, for example vitamin B3 (niacinamide) combines well with most forms of vitamin C and vitamin E (tocopherol), while plant stem cells make a good combination with many antioxidants, such as resveratrol, vitamin E and alpha-lipoic acid.