de Gruijl F R
Academisch Ziekenhuis, afd. Dermatologic/Allergologie, Utrecht.
Ned Tijdschr Geneeskd. 1998 Mar 21;142(12):620-5.
Many people consider a summer's day pleasant: warm and bright. The sun's ultraviolet rays do not contribute to the pleasure, and are biologically mainly harmful. As UV radiation does not penetrate any deeper than our skin, this organ has to be particularly well adapted to the UV exposure. The skin exploits the UV radiation for the synthesis of vitamin D3. Our day-to-day exposure suffices for this beneficial UV effect. Excessive exposure, as in sunbathing, only contributes to the adverse effects, like sunburn and suppression of cellular immunity in the short term, and 'photoaging' and skin cancer in the long term. The UVB radiation in sunlight is mainly responsible for these harmful effects, the UVA radiation to a far lesser extent (10-20% contribution). The UVA radiation from modern tanning equipment does not differ from that in sunlight, but UVA radiation does not lead to vitamin D3 production; it rather degrades vitamin D3 and a tan offers insufficient protection against the UVB radiation in full sunlight.
温暖且明亮。然而，太阳的紫外线却并非这份愉悦的贡献者，从生物学角度而言，紫外线主要是有害的。由于紫外线辐射穿透深度不会超过我们的皮肤，因此皮肤这一器官必须特别适应紫外线照射。皮肤利用紫外线辐射来合成维生素D3。我们日常的紫外线暴露量足以产生这种有益效果。过度暴露，比如日光浴，只会导致不良影响，短期内会引发晒伤和细胞免疫抑制，长期则会导致“光老化”和皮肤癌。阳光中的中波紫外线（UVB）辐射是造成这些有害影响的主要原因，长波紫外线（UVA）辐射的影响程度则小得多（贡献比例为10 - 20%）。现代美黑设备发出的UVA辐射与阳光中的并无差异，但UVA辐射不会促使维生素D3生成；相反，它会降解维生素D3，而且晒黑并不能为抵御直射阳光下的UVB辐射提供足够的防护。
