Tony O’Lenick asks industry expert Kelly Dobos, of Kao Brands, to explain the difference between humectants, emollients and occlusive agents, for the benefit of novice formulators.
Humectants include ingredients such as glycerin, urea and pyrrolidone carboxylic acid (PCA). These materials function by attracting water outward to the stratum corneum (SC) from the dermis below and binding that water in the SC. Glycerin, for instance, frequently is used due to its low cost and high efficacy. However, the tacky feeling imparted to skin by high levels of humectants is one of the drawbacks to formulating with them. Thus, when optimizing skin formulations, cosmetic chemists often are challenged to reduce these negative properties.
Occlusive agents increase moisture levels in skin by providing a physical barrier to epidermal water loss. Ingredients with occlusive properties include petrolatum, waxes, oils and silicones. Some occlusive agents like petrolatum can leave a heavy feeling on skin; thus they often are combined with other ingredients like emollients to improve consumer appeal.
Emollients provide some occlusivity and improve the appearance of the skin by smoothing flaky skin cells. Many different types of emollient esters and oils are available to formulators.1, 2 Emollients generally are grouped by their ability to spread on the skin. By combining emollients with the different spread rates, formulators can tailor the skin feel of a moisturizer. One can test for these differences by using different emollients in a standard base lotion. Additionally, emollient lipids similar to those naturally found in the skin may also increase the rate of barrier repair.3
Each of these ingredient types has a different mechanism of action and most cosmetic moisturizers will use a combination of them to create a synergistic effect and to mitigate certain esthetic or financial drawbacks. Product claims and skin feel are also considerations; therefore, experimentation with the various options is recommended.
1. TC Flynn, J Petros, RE Clark and GE Viehman, Dry skin and moisturizers, Clinics in Dermatology 19 387–392 (2001)
2. AV Rawlings, DA Canestrari and B Dobkowski, Moisturizer technology versus clinical performance, Dermatologic Therapy 17 49–56 (2004)
3. M Mao-Qiang, BE Brown, S Wu-Pong, KR Feinglod and PM Elias, Exogenous non-physiologic vs. physiological lipids: Divergent mechanisms for correction of permeability barrier dysfunction, Archives of Dermatology 131 809–81 (1995)