Why Formulation Matters: The Role of the Cosmetic Vehicle in Product Efficacy

When developing a new skincare product, the active ingredients are often the first thing people talk about. A brand may start with a particular peptide, vitamin, botanical extract or other ingredient and build the product concept around it.

But selecting a promising active is only the beginning.

What surrounds that active ingredient can be just as important. The formulation determines the environment in which the ingredient has to remain stable, and it can influence how the ingredient behaves once the product is applied to the skin. In other words, a good active ingredient does not automatically make a good cosmetic product.

This is one of the fundamental principles of modern cosmetic formulation.

(Dermatologic, Cosmeceutic, and Cosmetic Development: Therapeutic and Novel Approaches, 2008, edited by Kenneth A. Walters and Michael S. Roberts; Chapter 20, “Influence of Formulation Design on the Clinical Performance of Topically Applied Formulations,” Johann Wiechers)

A cosmetic formula is more than a carrier

It is tempting to think of a cream, serum or gel as simply a vehicle that carries active ingredients onto the skin.

From a formulation perspective, this is an oversimplification.

The vehicle can influence the physical and chemical environment of the active ingredient, as well as the way the finished product interacts with the skin. Factors such as solubility, polarity, pH, emulsion structure, viscosity, the choice of oils and emulsifiers, and the presence of solvents or other functional ingredients can all affect the final product.

The formulation therefore has its own role in the performance of the product. It is not merely a container for the ingredients.

This concept is also reflected in more recent formulation research. The behaviour of an active ingredient on the skin depends not only on the ingredient itself, but also on the formulation in which it is incorporated. The interaction between the active, the vehicle and the skin needs to be considered as a complete system rather than as three separate elements. (Rational Formulation Design, 2012, Majella E. Lane, James Hadgraft, G. Oliveira, R. Vieira, D. Mohammed and K. Hirata)

The same active ingredient does not necessarily perform the same way in every formula

Imagine two skincare products containing the same active ingredient at the same concentration.

It would be easy to assume that they should provide identical results.

In practice, that conclusion is not necessarily justified.

The surrounding formulation can change the conditions under which the active ingredient is present and delivered to the skin. The choice of vehicle can affect properties such as solubility, release, skin deposition and the residence time of the formulation on the skin.

This is particularly important when developing products containing ingredients with challenging physicochemical properties. An ingredient may have excellent scientific potential, but if it is poorly incorporated into the formulation or becomes unstable, the final product may not deliver the expected benefit.

The principle is simple:

The concentration of an active ingredient tells only part of the story.

The formulation in which that ingredient is delivered matters too.

Stability starts with formulation design

A product developer also has to think beyond the moment when the product is first manufactured.

An active ingredient may be sensitive to light, oxygen, heat, water activity or pH. It may interact with other ingredients in the formula or become less available over time. The formulation therefore has to provide an environment in which the ingredient can remain sufficiently stable throughout the intended shelf life.

This is one reason why formulation development involves much more than putting the desired ingredients together and adjusting their percentages.

A formulator may need to consider:

• the appropriate pH range;
• solubility and dispersion;
• compatibility between ingredients;
• sensitivity to oxidation;
• exposure to light and heat;
• emulsion stability;
• interaction with the packaging;
• and the conditions under which consumers will store and use the product.

These considerations are interconnected. Changing one component of a formula can sometimes affect several other characteristics at the same time.

The skin itself is part of the equation

A topical cosmetic is applied to a biological surface, not an inert material.

The outermost layer of the skin, the stratum corneum, provides an important barrier between the body and the external environment. Consequently, an ingredient applied to the skin does not simply move freely through it.

The formulation and the condition of the skin can influence this interaction.

Skin hydration is one example. Cosmetic vehicles can contribute to skin hydration in different ways. Some formulations provide water directly, while emollient ingredients can help reduce water loss by forming a film on the skin. Humectants such as glycerol can attract and retain water within the outer layers of the skin. (Dermatologic, Cosmeceutic, and Cosmetic Development: Therapeutic and Novel Approaches, 2008, edited by Kenneth A. Walters and Michael S. Roberts; Chapter 21, “Dry Skin and Moisturizers,” Anthony Vincent Rawlings and Paul John Matts)

This illustrates an important point: the formulation can influence the condition of the skin at the same time as it delivers the active ingredient.