2.1.3　Pigment and skin color

As the protective barrier of our body，the skin protects organisms from environmental stimuli，such as ultraviolet，toxins，and microbes.Skin pigmentation plays an important role in the defense against ultraviolet.In human skin，melanogenesis is a tightly regulated process.Many internal and external factors are involved in the melanogenesis process，and many physiological and external events can modify skin melanogenesis，leading to hyperpigmentation or hypopigmentation，and finally resulting in dermatosis.(https://www.daowen.com)