About Cosmetic Formulation and the Skin/Part 1

Learn how to formulate more consciously and improve your formulation efficacy.

Being a cosmetic formulation chemist is exciting; we get to choose the ingredients and textures when we create! But from my own experience, I know that too little thought is spared on the outcome of mixing ingredients together and applying a particular formulation format. I believe we can do it more consciously by trying to understand the interactions between ingredients and their impact on the skin barrier and penetration.

Why? To improve product efficacy as well as consumer safety.

Is it easy for ingredients to penetrate?

I don’t need to elaborate on the fact that our skin structure very effectively prevents the penetration of substances because of its truly unique and remarkable structure. Sometimes it is desirable to transport those actives into the skin for improved efficacy, but other times we want them to stay on the surface only (such as UV filters in SPF products). Either way, it is important to be aware of how formulation type and the addition of different ingredients might affect the penetration potential of substances (including preservatives!) and skin permeability.

Let's start with trying to understand what happens when a formulation is applied on the skin.

Emulsions

Emulsions, when applied, are spread over, forming a film. As the temperature increases to the skin temperature, water and other volatile ingredients start to evaporate. Almost all water escapes within 5 to 10 minutes. During this period, the viscosity and sometimes the structure change. In o/w emulsion, when water evaporates, the product becomes packed together more densely, leading to a viscosity increase, and when the water content drops below 15%, w/o emulsion is formed. This is different with the w/o emulsion. Here, the oil is the outer phase, and during drying, viscosity drops. After application on the skin, an active ingredient begins to diffuse out of the base into the top layers of the skin, and its rate depends on many factors: the substance's nature (ionic, non-ionic, polar or non-polar), interactions with the base, concentration, and affinity to the skin's structures.

Hydrogels

When a hydrogel formula is applied on the skin, free water evaporates, and the hydrated polymer creates an elastic film on the surface that keeps the skin moisturised and gradually releases active ingredients into the skin. That way, the contact time of the active with the skin is increased. Just to remind you, gels are based on polymeric thickeners that are characterized by high water absorption capacity. Due to the presence of hydrophilic functional groups, water molecules and water-soluble actives can migrate into the network. They display a three-dimensional structure that mimics the native extracellular matrix of the skin, especially biopolymers such as collagen, gelatin, hyaluronic acid, alginate, chitosan, xanthan gum, pectin, starch, and cellulose.

In the next part we will look into the formats themselves and focus on how they may affect ingredients penetration.

Let's create beauty together.