ABSTRACT
The skin is one of our key defensive barriers that protects the internal living organism from the external environment and assists in maintaining its homeostasis. Although a key role of its outermost layer is to prevent the entry of foreign substances into the body, this barrier is imperfect and can allow certain topically applied substances. In addition, substances entering the body via the skin avoid ‘rst-pass hepatic metabolism
1.1 Introduction ......................................................................................................1 1.2 Skin Structure ...................................................................................................3
