Formulating for efficacy¹

Abstract

Active ingredients have been around in cosmetics for a long time but have they really resulted in active cosmetic products? In order to achieve this, the right active needs to be delivered to the right location at the right concentration for the correct period of time. And the extent (and therefore the concentration) of this delivery depends on the formulation. From a rather theoretical approach based on the polarity of the active ingredient, the stratum corneum and the oil phase, the Relative Polarity Index was established that enables the selection of a suitable emollient for ensuring skin penetration of the active ingredient. Practical examples subsequently show the validity of this approach that demonstrates that one can regulate the delivery of an active molecule (and therefore the efficacy of a cosmetic formulation) by selection and control of the emollient system. Cosmetic formulations are generally quite complex mixtures and subsequent experiments using different emulsifier systems indicated that this component of a cosmetic formulation could also have an impact on steering the active ingredient to the right layer of the skin, although it is too early to be able to derive general rules from this.

Dermal and Transdermal Delivery of Active Substances from Semisolid Bases

“…Transport of active substances through the skin may be described as series of consecutive steps, each of which can potentially be rate limiting [2] . First, the drug needs to diffuse from the formulation to the skin surface [2] .…”

“…First, the drug needs to diffuse from the formulation to the skin surface [2] . This process is characterized by the release rate.…”

“…After being released, the active substance partitions into and diffuses through the stratum corneum, the principal skin barrier, which represents the thin outer layer (10 µm) of the epidermis and is typically comprised of about 10-25 corneocyte cell layers [1,2] . The stratum corneum structurally composed of tightly packed alternating hydrophilic and lipophilic layers organized as "bricks and mortar" [1][2][3][4][5] .…”

“…The stratum corneum structurally composed of tightly packed alternating hydrophilic and lipophilic layers organized as "bricks and mortar" [1][2][3][4][5] . Human stratum corneum consisted of corneocyte "bricks" composed primarily of aggregated keratin filaments encased in a cornified envelope that are surrounded by an extracellular milieu of lipids organized as multiple lamellar bilayers serving as mortar [5] .…”

Label free non-invasive imaging of topically applied actives in reconstructed human epidermis by confocal Raman spectroscopy

“…Their penetration properties depend amongst others on their molecular weight and their hydrophilic/lipophilic character 5 . In addition, the penetration can be enhanced by vehicles added to the drug's formulation [6][7][8] . But, accelerated penetration is not in every case desirable.…”