初中《生理卫生》的《皮肤》一章,在讲述皮肤的结构特点时提到:“常受日光照射的皮肤,黑色素增加,皮肤颜色就变得黑些。黑色素能吸收紫外线,可以避免因紫外线穿透皮肤而损伤内部组织。”“表皮细胞内含有一种胆固醇(维生素D前身),经日光照射后能转变成维生素D。因此,儿童常晒太阳对预防佝偻病有一定的作用” Mentioned in the chapter on “Skin” of “Physiological Health” in junior high school mentions the structural features of the skin: “Often exposed to sunlight, the skin becomes darker as the amount of melanin increases, and melanin absorbs ultraviolet light, Penetrate the skin and damage the internal tissue. ”“ Epidermal cells contain a cholesterol (vitamin D precursor), after the sun can be transformed into vitamin D. Therefore, children often have the sun to prevent rickets have a role ”