Use of hydrotalcites and clay materials in cosmetics: an overview
Hydrotalcites and clays are biocompatible materials and possess unique characteristics that allow for relevant applications in cosmetics and health care. This review is focused on the use of hydrotalcites, hydroxyl double salts and zirconium phosphate layered compounds for cosmetic purposes. These synthetic clays show superior properties compared with natural minerals in terms of chemical and microbiological purity and ability to encapsulate active ingredients with very high loading. The use of layered clays as carriers of cosmetic ingredients allow for an enhancement of the stability and the photostability of the actives. Moreover, the encapsulation/intercalation of the ingredients in the interlayer region is a useful tool to improve their bioavailability, to control and modify the active release greatly increasing the efficacy and the safety of the cosmetic formulations.
The use of clay minerals for curative and protective aims is known since antiquity. In fact, there is evidence that prehistoric humans discovered the ability of muds, composed by a mixture of clay and water, to heal wounds, irritations, infections, pains and to cleanse the skin. Egyptian physicians employed medicinal clay as anti-inflammatory or antiseptic agent (1-3) and even Cleopatra used muds from the Dead Sea for cosmetic purposes (4). The first pharmacopoeias were born only in the XVII century, thanks to work done by the scientific academies. In these books the classification, the coding of the raw materials, including clay minerals, and the official procedure for the different medical products were reported. After discovery of the crystallography, between the XVIII and the XIX centuries, a big step forward was made in the study of the structure and the properties of clay minerals and their potential use in health care applications. Advances in the field of chemistry allowed the development of synthetic methods to replicate and produce clay materials avoiding structural defects, chemical and microbiological impurities, usually present in the nat ...