Comparatively Speaking: Humectants vs. Emollients vs. Occlusive Agents

By: Kelly Dobos, Kao Corp., and Anthony J. O'Lenick Jr., Siltech LLC

Posted: September 22, 2010

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Humectants include ingredients like glycerin, urea, and pyrrolidone carboxylic acid (PCA). Humectants work by attracting water from the dermis below and helping to keep that water bound in the Stratum corneum. Glycerin is used frequently because of its low cost and high efficacy, but a tacky feel on the skin is one of the drawbacks of formulating with high levels of humectants. When optimizing skin formulations, cosmetic chemists try to reduce these negative properties of humectants.

Occlusive Agents

Occlusive agents increase moisture levels 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 impart a heavy feel, so they are often combined with other ingredients such as emollients to improve consumer appeal.

Emollients

Emollients provide some occlusivity and improve the appearance of the skin by smoothing flaky skin cells. There are many different types of emollient esters and oils available to a formulation chemist.^{3, 4} Emollients generally are grouped by their ability to spread on the skin. By combining emollients with the different spread rates, a cosmetic formulator can tailor the skin feel of a moisturizer. The formulator 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.⁵

Putting it together

Each of these ingredient types has a different mechanism of action, and most cosmetic moisturizers will use a combination of these ingredients to create a synergistic effect and mitigate certain aesthetic or financial drawbacks. Product claims and skin feel are also considerations to be aware of, so do not be afraid to experiment with options when creating a moisturizer. For tips on creating successful skin formulations, see the previous article on HLB formulating.

References
1. CR Harding, The Stratum Corneum: Structure and Function in Health and Disease, Dermatologic Therapy, 17 6–15 (2004)
2. RR Wickett and MO Visscher, Structure and Function of the Epidermal Barrier, American Journal of Infection Control, 34(10) S98–S110 (2006)
3. TC Flynn, J Petros, RE Clark and GE Viehman, Dry Skin and Moisturizers, Clinics in Dermatology,19 387–392 (2001)
4. AV Rawlings, DA Canestrari, B Dobkowski, Moisturizer Technology versus Clinical Performance, Dermatologic Therapy 17 49–56 (2004)
5. 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 131 809–816 (1995)