Human skin, just like any other surface, has a specific energy that can be measured. And it is just this physical property that, in combination with the surface tension of the cosmetic product, is responsible for its wettability.

However, a single energy value for the human skin is not enough. Various skin types must also be taken into account: skin can be dry, greasy, normal or even mixed. If the energy profiles of all these skin types are known then the wetting behavior with various liquids can be predicted. This ensures that different cosmetics can be perfectly matched to the particular user.

With the aid of a drop shape analysis system contact angles are determined on the skin for different liquids. The surface free energy can then be determined directly from these values, provided that the polar and disperse fractions of the liquids are known.


A collection of data for all skin types drawn up in this way makes it possible to selectively alter the formulation of cosmetics by making use of molecular parameters such as polar behavior. This means that the number of measurements that have to be carried out on volunteers can be dramatically reduced.

The following table shows the differences in energy resulting from different degrees of greasiness of the skin:

Tab. 1: Surface free energies of two skin types


If the polar fractions of the surface tension are plotted against the disperse fractions then the result is the “wetting envelope”, which is shown here using non-degreased skin as an example. (see Figure 3). All liquids whose data lie beneath the curve will provide complete wetting