Wolf Ronni, Matz Hagit, Orion Edith, Lipozencić Jasna
Dermatology Unit, Kaplan Medical Center, 76100 Rechovot, Israel.
Acta Dermatovenerol Croat. 2003;11(3):158-62.
One decade ago, a sun protection factor (SPF) of 15 was considered a complete blocker of ultraviolet radiation (UV). The logic behind that cutoff point was that sunscreens with this SPF number would always prevent erythema and that preventing erythema would prevent all the ill effects of UV exposure. Today, we know that both of these assumptions were wrong and we tend to recommend higher SPF. Consumers apply only about one-quarter to one-half thickness of the layer of sunscreen material used to measure the SPF in the laboratory. That means that less than 50% of the SPF number claimed on the label is spread on the consumer's skin, meaning that a sunscreen with an SPF 30 will give the real protection of an SPF of 15. Therefore, recommend 60 when you want a real protection of 30! Significant injury, DNA damage, mutations, and carcinogenesis can and do occur also with cumulative suberythemal UV exposure. Thus, erythema induction, a criterion that defines SPF, is not a good indicator of UV damage. We also need higher SPF values to prevent the damage caused by suberythemal doses of UV. The value of the SPF claimed on the label is diminished by environmental factors that are not taken into account during SPF measurements in the laboratory, such as sweating, water immersion, rubbing off, and photodegradation. There are some misunderstandings and confusion about the mode of action of physical sunscreens. It was originally considered that, in contrast to organic sunscreens, the inorganic metal oxides (zinc oxide and titanium dioxide) acted as scatterers or reflectors of UV light, as a mirror. This is not the case with modern micronized forms of metal oxides. It has been shown that both zinc oxide and titanium dioxide mobilize electrons within their atomic structure while absorbing UV radiation. Thus, although metallic oxides are not inert per se, in their coated form they are stable, non-toxic, and safe and they act as highly efficient UV attenuators. Therefore, we recommend our patients to use this type of sunscreens. We should exert all our influence upon our patients not to expose themselves to excessive sunlight, to routinely use generous layers of sunscreen agents, and to wear protective clothing. To wait for the dust to settle around the issue of the effectiveness of sunscreens in preventing melanoma, while the ideal sunscreens--topical, systemic, whatever--are at our disposal, is a luxury we cannot afford.
十年前，防晒系数（SPF）为15被认为是紫外线（UV）的完全阻挡剂。该临界点背后的逻辑是，具有此SPF值的防晒霜总能预防红斑，而预防红斑就能预防紫外线暴露的所有不良影响。如今，我们知道这两个假设都是错误的，我们倾向于推荐更高的SPF值。消费者涂抹的防晒霜材料层厚度仅为实验室测量SPF时所用厚度的约四分之一到二分之一。这意味着标签上声称的SPF值中，只有不到50%涂在了消费者的皮肤上，也就是说，一款标注SPF 30的防晒霜实际提供的防护效果相当于SPF 15。所以，若想要获得相当于SPF 30的实际防护效果，就应推荐使用SPF 60的产品！累积的亚红斑紫外线暴露也确实会导致严重损伤、DNA损伤、突变和致癌。因此，作为定义SPF的标准，红斑诱导并不是紫外线损伤的良好指标。我们还需要更高的SPF值来预防亚红斑剂量紫外线造成的损伤。标签上声称的SPF值会因实验室测量SPF时未考虑的环境因素而降低，如出汗、水浸、擦掉以及光降解。对于物理防晒霜的作用方式存在一些误解和混淆。最初人们认为，与有机防晒霜不同，无机金属氧化物（氧化锌和二氧化钛）像镜子一样起到紫外线的散射或反射作用。现代微粉化形式的金属氧化物并非如此。研究表明，氧化锌和二氧化钛在吸收紫外线时都会在其原子结构内激发电子。因此，尽管金属氧化物本身并非惰性物质，但以涂层形式存在时它们是稳定、无毒且安全的，并且能作为高效的紫外线衰减剂。所以，我们建议患者使用这类防晒霜。我们应尽全力影响患者，使其避免过度暴露在阳光下，日常使用足量的防晒剂，并穿着防护服。在有理想的防晒霜——局部用、全身用，无论哪种——可供我们使用的情况下，等待防晒霜预防黑色素瘤有效性问题的尘埃落定是我们承担不起的奢侈行为。
