Introduction

摘要

Human skin is the largest and most prominent organ of the human body (Figure 1.1). Its chief function is that of a barrier, designed to maintain the integrity of the body through separation of the harsh, disordered outside world from the delicate order within. The deeper and relatively static layer, the dermis, confers form, elasticity and resilience to skin, whereas the upper layer, the epidermis, is constantly renewing itself and is more concerned with the maintenance of the water gradient between the dermis and the outer world. As the outer integument, the epidermis is subjected to constant physical, chemical and ultraviolet trauma, and, without it, Homo sapiens would rapidly perish from the face of the Earth. Within the epidermis are a number of structural and biochemical systems that have evolved to protect us in varying environmental conditions.