INTRODUCTION
The skin forms the border between the organism and the external environment. It acts as a protective covering that separates the internal body from outside influences.The skin performs several essential functions:Prevents dehydration by limiting water loss from the body, Stops penetration of noxious foreign materials and microorganisms, acting as a protective barrier,Cushions against mechanical shock, providing physical protection, Helps maintain constant body temperature through regulatory mechanisms.Transduces incoming stimuli, allowing the body to sense touch, pressure, pain, and temperature.Understanding structure and function is essential because effective formulation depends on how ingredients interact with the skin.Concerns of cosmetic chemists include:Improvement of skin by pharmacology, using suitable actives,Prevention of damage that may result from external factors or cosmetic use.