Formulation strategy of cosmetic emulsions: an introduction
Dr. Luigi Rigano
Vehicles and active principles are common concepts in the pharmaceutical field, influencing also the cosmetic world. Indeed, the concept of cosmetic structure is a lot wider than that. Firstly, the different body areas where products are applied define their rheology, and structural characteristics. As such application is guided by sensory perceptions, this requires to create the cosmetic formula as an ‘informed machine" able to interact with both the hands and consumer’s perceptions. That needs a careful study of parameters like evaporation speed, absorption, spreading, shine, dry or wet feel. Moreover, a common formulation’s need is the adoption of the criteria of "multi-functionality" in ingredients selection. Finally, the need of the applied product to interact with the extended cutaneous surface, leads to the intensive development of physical forms with high surface extensions, just like emulsions. These merge two wide physical domains in the ingredients world: liposoluble and hydro-soluble substances. They are fed into a structured system, divided into compartments, with ‘underpinned’ stability. Micro-disperse combinations of oils and aqueous solvents create an extended and fascinating whole. The resulting universe might be classified according to the external phase (oil or water) or flow (milks, lotions, creams, butters) or evaporating solvent (water, alcohol, silicones) or emulsifier type (momomer, polymeric, soap, silicone, poly-glyceryl, combined). Or even by application site (face, body, eyes) or functional characteristics (moisturizer, anti-age, sunscreen) or even consumers’ section (baby o aged, men or women, healthy or ‘unbalanced’).
Industrial production of such systems is also complex and fascinating, just for its wayward behaviour of ingredients, largely unforeseeable on a theoretical basis. Addition sequence, temperature, homogenization and mixing speed, swelling and de-aeration sequence, cooling cycles, time and reason-why of individual phases are difficult preparation challenges. Solutions cannot be studied systematically but require insight, technical culture and spirit of observation.
