J. Cosmet. Sci., 62, 549–563 (November/December 2011) 549 Advanced carrier systems in cosmetics and cosmeceuticals: A review DANHUI LI, ZIMEI WU, NATALY MARTINI, and JINGYUAN WEN, School of Pharmacy, Faculty of Medical and Health Sciences, The University of Auckland, 93 Grafton Road, 1010 Auckland, New Zealand. Accepted for publication June 21, 2011. Synopsis Carrier systems refer to carrier vesicles such as liposomes, nano/microparticles, emulsions, etc., that are cou- pled with active agents and applied to products to achieve the promoted effects of the active ingredients. This article reviews the recent research on carrier systems, focusing on cosmetic and cosmeceutical applications the pros and cons of each carrier system and products on the market utilizing the technologies are dis- cussed. INTRODUCTION Cosmetic usage has a long history. The fi rst evidence dates back to 3500 BC in ancient Egypt, where predominantly the royalty used makeup including unguent, kohl, and soot to beautify and enhance their skin’s appearance (1). Since then, people’s enthusiasm, es- pecially women’s, and demand for cosmetic products, has led to a prosperous growth in this industry (2). According to the Food and Drug Administration (FDA), cosmetics are defi ned as “articles intended to be rubbed, poured, sprinkled, or sprayed on, introduced into, or otherwise applied to the human body for cleansing, beautifying, promoting at- tractiveness, or altering the appearance and articles intended for use as a component of any such articles except that such term shall not include soap” (3). However, many prod- ucts exhibit functions surpassing that of solely covering and camoufl aging defects in ap- pearance and they often contain therapeutic or “active” ingredients to heal or repair skin tissue. They are in fact more than pure cosmetics and, with this in mind, the term “cos- meceutics” was coined (4). Cosmeceutical products are considered to be the hybrid of cosmetics and topical medication applied topically, they contain ingredients and tech- nology that infl uence the biological and physiological function of the skin. Due to both their skin-altering and skin-healing function, these products are considered to be futuristic (5). Address all correspondence to Jingyuan Wen at j.wen@auckland.ac.nz.

JOURNAL OF COSMETIC SCIENCE 550 Though the effects of these products are fascinating, given the barrier function of the skin they are diffi cult to achieve merely by adding functional compounds to the products. The human skin is comprised of three tissue layers: the epidermis, the dermis, and the subcu- taneous layer. The stratum corneum, the outermost layer of the epidermis, is the essential permeability barrier that limits the passage of most compounds. Normally, the penetrant that is applied to the skin surface may trespass the stratum corneum through three path- ways: via appendages or through transcellular or intercellular routes (6). Although the pores of appendages bypass the stratum corneum, their openings onto the skin surface are very small (0.1% of total skin surface) (7), which renders this pathway negligible. With the transcellular route, a penetrant has to infi ltrate into corneocytes, diffuse through keration, and then penetrate the next corneocyte. This route is not considered as a main pathway either and is merely suitable for highly hydrophilic compounds. The intercel- lular route is the principal pathway through which the compound goes through the con- tinuous and tortuous domain formed by the intercellular lipid matrix (5). In fact, only small and lipophilic compounds are able to penetrate the stratum corneum therefore, this poses a problem for cosmetic and cosmeceutical products: how to overcome the skin barrier and facilitate the active ingredients deep into skin where they can exhibit their functions. The use of carrier systems is one of the strategies investigated to enhance the penetration of compounds through the stratum corneum. Carrier technology, also re- ferred to as nanotechnology if the vesicle or particle is under nanoscale, refers to the cou- pling of agents to carrier particles such as liposomes, niosomes, and solid lipid nanoparticles (SLN) (8) and is the main method of delivering ingredients into the skin. This is one reason why carrier systems are benefi cial in skin and body care products. Besides enhancing penetration (9,10), carrier systems may have other uses in cosmetic and cosmeceutical products such as improving agent stability (11), as targeting agents (12), and in modulating drug release (8). APPLICATION OF CARRIER SYSTEMS IN COSMETICS AND COSMECEUTICALS LIPOSOMES Liposomes (Figure 1), fi rst described by Bangham and Papahadjopoulos in the 1960s (13), are microscopic vesicles formed by phospholipid bilayers surrounding an aqueous medium. The ability of phospolipids to form a bilayer structure is attributed to their amphipathic character. The polar/hydrophilic head region assembles towards the aqueous phase, while the nonpolar/lipophilic tail part orientates towards the inside (13). Lipo- somes were investigated for the fi rst time in 1980 as a topical delivery system for derma- tological agents into the skin (14). Since then, studies on liposomes for dermal application have progressed. The advantages of using liposomes for dermal application are summarized as follows: 1. Liposomes are biodegradable and nontoxic. 2. Due to the amphiphilic property of phospholipids, of which the bilayer is constituted, liposomes contain domains for both lipophilic and hydrophilic substances, meaning they can be used as carrier systems for active ingredients with different solubilities (8). 3. Liposomes provide controlled release profi les for many substances.