The structure and function of the skin details the individual components of the epidermis, dermis, and their roles in normal skin health. The individual cell types in the epidermis, the different epidermal layers, and the roles of the keratinocyte are explained. The epidermis and dermis, and their important relation to each other through the dermoepidermal junction are described. The dermal adnexal structures of hair follicles (pilosebaceous units), sweat glands, and nerves are all considered. The functions of skin and barrier function are also listed. Rare but important causes of disordered sweating (hyperhidrosis and hypohidrosis) are described. In addition, presentations of hyperhidrosis are discussed.

Structure and function of the skin

Nanosystems such as microemulsions (ME) and nanoemulsions (NE) offer considerable opportunities for targeted drug delivery to and via the skin. ME and NE are stable colloidal systems composed of oil and water, stabilised by a mixture of surfactants and cosurfactants, that have received particular interest as topical skin delivery systems. There is considerable scope to manipulate the formulation components and characteristics to achieve optimal bioavailability and minimal skin irritancy. This includes the incorporation of established chemical penetration enhancers to fluidize the stratum corneum lipid bilayers, thus reducing the primary skin barrier and increasing permeation. This review discusses nanosystems with utility in skin delivery and focuses on the composition and characterization of ME and NE for topical and transdermal delivery. The mechanism of skin delivery across the stratum corneum and via hair follicles is reviewed with particular focus on the influence of formulation.

https://www.mdpi.com/1999-4923/9/4/37/pdf

Topical Nano and Microemulsions for Skin Delivery.

Nanoparticle-Induced Autophagy in Biomedical Research Karen Peynshaert,†,‡ Bella B. Manshian, Freya Joris,†,‡ Kevin Braeckmans,†,‡ Stefaan C. De Smedt,*,†,∥ Jo Demeester,† and Stefaan J. Soenen*,†,§ †Lab of General Biochemistry and Physical Pharmacy, Faculty of Pharmaceutical Sciences, ‡Centre for Nanoand Biophotonics, and Ghent Research Group on Nanomedicine, Ghent University, B9000 Ghent, Belgium Biomedical MRI Unit/MoSAIC, Department of Imaging and Pathology, Faculty of Medicine, Catholic University of Leuven, B3000 Leuven, Belgium

Exploiting intrinsic nanoparticle toxicity: the pros and cons of nanoparticle-induced autophagy in biomedical research.

https://espace.library.uq.edu.au/view/UQ:426038/UQ426038_OA.pdf

Topical and cutaneous delivery using nanosystems

Abstract In the past decades, much attention has been paid to toxicity assessment of nanoparticles prior to clinical and biological applications. While in vitro studies have been increasing constantly, in vivo studies of nanoparticles have not established a unified system until now. Predictive models and validated standard methods are imperative. This review summarizes the current progress in approaches assessing nanotoxicity in main systems, including the hepatic and renal, gastrointestinal, pulmonary, cardiovascular, nervous, and immune systems. Histopathological studies and specific functional examinations in each system are elucidated. Related injury mechanisms are also discussed.

https://www.degruyter.com/downloadpdf/j/ntrev.2017.6.issue-3/ntrev-2016-0047/ntrev-2016-0047.xml

Toxicity assessment of nanoparticles in various systems and organs

The effect of formulation on the penetration of coated and uncoated zinc oxide nanoparticles into the viable epidermis of human skin in vivo

Effect of flexing and massage on in vivo human skin penetration and toxicity of zinc oxide nanoparticles

It is critical to develop an effective understanding of the interaction between the drug, delivery system and skin in order to predict and assess skin penetration and permeation. Experimental models for the assessment of topical and transdermal delivery systems must permit evaluation of these complex interactions. Whilst in the past, animal models were commonly used, recent regulatory guidelines, based on 3R principles (refinement, reduction, replacement), encourage the rational use of animals. Alternative methods have been proposed for use in the development of topical and transdermal delivery systems which are often used in combination. We will review the current state of the art in alternative methods for topical and transdermal delivery systems development, including technologies that can assist in the characterization of skin penetration/permeation studies.

Alternative Methods to Animal Studies for the Evaluation of Topical/ Transdermal Drug Delivery Systems.

The cosmetic industry continues to expand worldwide. The claims described on a cosmetic product label or in promotional material must be substantiated with scientific data or clinical studies, ensuring that the product actually has the promised effect. Cosmetics must be safe to use over a long term, so safety assurance is critical. Testing the skin penetration of cosmetic actives and excipients is one example of the safety measures that are required. With the prohibition of animal testing for cosmetic evaluation in Europe, product safety has had to be assessed by in vitro methods or in vivo human studies. This has led to a new set of challenges to find and validate in vitro techniques that reliably predict in vivo human responses.

Vania R. Leite-Silva

Papers

The effect of formulation on the penetration of coated and uncoated zinc oxide nanoparticles into the viable epidermis of human skin in vivo

Effect of flexing and massage on in vivo human skin penetration and toxicity of zinc oxide nanoparticles

Alternative Methods to Animal Studies for the Evaluation of Topical/ Transdermal Drug Delivery Systems.

Chapter 46 – Skin Penetration