Washington Master Esthetics Practice Exam

The ability of a cosmetic ingredient to penetrate the stratum corneum, which is the outermost layer of the skin, is influenced by several factors. The factors listed in the options, apart from the identified correct answer, all play a significant role in this process.

The molecular size of an ingredient is crucial, as smaller molecules are more likely to penetrate through the spaces between the cells in the stratum corneum. Therefore, this aspect directly impacts an ingredient's ability to be absorbed by the skin.

Ingredient's capacity for hydration also affects penetration, as ingredients that can provide moisture help keep the skin barrier healthy and can facilitate the absorption of other components.

While the pH level of an ingredient affects skin compatibility and can influence its interaction with skin cells, it is not primarily a direct factor in determining absorption through the barrier.

In contrast, the ability of an ingredient to break down into its elemental components does not impact its penetration ability through the stratum corneum directly. Instead, it's the state and characteristics of the ingredient in its formulated state that matter most when considering how effectively it will be absorbed by the skin. Thus, this option stands out as not being a direct factor affecting penetration.