9.1 Overview of Cosmetic Dermatology
Cosmetic dermatology is a science that studies the anatomical structure and physiological function of human skin and implements the maintenance，improvement，repair and shaping of human skin health and beauty and regularity based on the theory of dermatology and the combination of medicine and aesthetics.It is a main clinical application discipline of aesthetic medicine.The main areas of cosmetic dermatology include skin beauty basic theory，skin health and beauty，hair health and beauty，laser and photon beauty treatment technology，beauty application technology，skin surgery，beauty Chinese medicine and treatment of skin diseases with lesions，et al.
According to the literature，cosmetic dermatology has a long history.In China，it is said to start from Dayu period（2277 BC to 2213 BC）.According to the legend，when Dayu was at his 50th，wrinkles appeared in the corners of his eyes and forehead one after another.At that time，it was suggested to touch the face with wax grease to lighten the wrinkles.But the skin got hard after touching the wax.After many tests，someone suggested that the wheat flour and the dough should be applied to the face.This is the legend of the“Yu selects powder”in the ancient literature.In the Tang Dynasty，the great medical scientist Sun Simiao presented more than 80 skin beauty prescriptions in Thousand Golden Preions，which is the earliest known literature on beauty prescriptions in China.Li Shizhen's Compendium of Materia Medica in the Ming Dynasty also recorded more than 700 beauty prescriptions.
According to historical records，the ancient Egyptians had the earliest conscious of using cosmetics.The ancient Egyptians loved aromatic products.They kept collecting natural spices from India，Arabia and other places，and used them to make perfumes and cosmetics.The ancient Egyptians attached great importance to the health and beauty of the skin.After bathing，they applied a lot of sesame oil，perfumes or ointment to moisturize the skin.In order to resist the hot and dry climate，they applied animal grease to the skin to prevent skin dryness.(https://www.daowen.com)
In general，the development of modern cosmetic dermatology is mainly divided into five generations.The first generation：the age of ordinary oil and skin care.It is characterized by the use of pure physical properties of cosmetics（e.g.，animal oil）which taken from natural unprocessed oil（heating at most），mainly to achieve moisturization and prevent cracking.The second generation：oil-water mixture skin care era.It is the first generation of cosmetics produced by industrial integration.It also has the effect of moisturizing and preventing chapped，but it is more hygienic，convenient and pure than the first generation.The representative products of this generation include petroleum jelly.The third generation：the era of natural plant cosmetics.It is the first generation of cosmetics produced by high-tech plant purification technology.It is characterized by hygiene，convenience，beauty，high purity，certain effects，and complex raw materials.The representative products of this generation include the earlier cucumber facial cleanser.The fourth generation：the era of biohormone ecological cosmetics.It is the first generation of cosmetics produced by high-tech biological engineering technology.It is characterized by hygiene，convenience，beauty，high purity，strong efficacy，complex raw materials，easy absorption，and pure fragrance.The fifth generation：nanotechnology natural essence cosmetics era.It is the first generation of cosmetics dealt with molecular micro-processing technology，and it is also the application of the most advanced chemical technology in the field of cosmetics.