适度的日晒对人体健康是有益的。但是,长时间在日光下曝晒,轻则引起头痛、恶心、头晕,视力减弱,睡眠失调,使原有的慢性疾病加重;重则引起眼睛损伤和免疫系统的破坏,甚至引起皮肤癌变。长时间曝晒,紫外线可通过两种途径损伤皮肤;一是辐射损伤支持真皮的细胞,使皮肤干燥、发硬,出现皱褶;二是辐射损伤皮肤细胞中的脱氧核糖核酸,使皮肤细胞发生变异,生长失控而成皮癌。人体皮肤经过长时间曝晒,会蒙上一层黑色的 Moderate sun exposure is good for human health. However, prolonged exposure to the sun can cause headache, nausea, dizziness, poor eyesight and sleep disorders, leading to the exacerbation of chronic diseases. Heavy damage to the eyes and destruction of the immune system can even cause skin canceration. Prolonged exposure to ultraviolet light can damage the skin in two ways; one is radiation damage to the dermis-supporting cells, making the skin dry, stiff and wrinkled; second, radiation damages DNA in the skin cells, causing skin cells to mutate , Out of control growth from skin cancer. After a long period of human skin exposure, will be cast a layer of black