Application of sunscreen − theory and reality
SUMMARY
摘要
英文原文
We present research on sunscreen use with possible pitfalls and discuss theory vs. reality. A literature review in PubMed was conducted using the terms ‘sunscreen application’, ‘sunscreen use’ and ‘sun protection factor’. The sun protection factor (SPF) of sunscreens are tested using a thickness of 2 mg/cm2, but investigations show that sunscreen under natural conditions is applied insufficiently with amounts about 0.39 to 1.0 mg/cm2, which decreases the protection factor considerably. It has been shown that early reapplication or use of very high SPF (70–100) may partly compensate for the discrepancy between the amounts of sunscreen applied during testing and in reality, and that sunscreen application can be improved by education of consumers. Missing areas and ultraviolet radiation exposure before sunscreen application are other pitfalls that reduce the protective effect of sunscreens considerably. Current sunscreen labelling overrates the protective effect of a given sunscreen when the reality of sunscreen use is taken into account. This may possibly mislead consumers to feel it is safe to extend sun exposure. Alternatively to educating people to use large amounts of sunscreen, we suggest a simple teaching strategy: (1) Apply before sun exposure and (2) Reapply once within 1 h.
对应中文
我们介绍了关于防晒霜使用可能存在的缺陷的研究，并讨论了理论和现实。PubMed上的一篇文献综述使用了“防晒霜应用”、“防晒霜使用”和“防晒因子”这三个术语。防晒霜的防晒系数（SPF）是使用2mg/cm²的厚度进行测试的，但调查表明，在自然条件下，防晒霜的用量约为0.39至1.0mg/cm²，这大大降低了防晒系数。研究表明，及早重复使用或使用极高SPF（70-100）的防晒霜可以部分弥补测试过程中使用的防晒霜与实际使用的防晒霜数量之间的差异，并可以通过教育消费者来改善防晒霜的应用。目前的防晒霜标签高估了特定防晒霜的保护效果，但考虑到防晒霜的实际使用情况。这可能会误导消费者，让他们觉得延长日晒时间是安全的。除了教育人们大量使用防晒霜之外，我们建议一个简单的教学策略：(1)在阳光照射前涂抹，(2)在1小时内重新涂抹一次。
英文原文
There are several ways to protect the skin from solar ultraviolet radiation (UVR). The main recommendations are to seek the shade, to avoid sun exposure around noon and to apply sunscreen. Sunscreen application is usually the preferred way of sun protection. The World Health Organization (WHO) recommends that sun- screen should be applied 20 min before sun exposure with reapplication every second hour, and repeated after swimming or bathing. The protection afforded by sunscreen is expressed as the sun protection factor (SPF), which is the factor by which the sun exposure dose can be increased before skin erythema develops. The minimal erythema dose (MED) is the UVR dose needed to provoke just perceptible erythema.
对应中文
有几种方法可以保护皮肤免受太阳紫外线辐射(UVR)的伤害，主要建议是找个阴凉处，避免中午时分暴露在阳光下，以及涂抹防晒霜。涂抹防晒霜通常是防晒的首选方式。世界卫生组织(WHO)建议在阳光照射前20分钟涂抹防晒霜，每隔一小时重新涂抹一次，并在游泳或洗澡后重复涂抹防晒霜。防晒霜提供的保护被表示为防晒因子(SPF)，这是在皮肤红斑形成之前可以增加太阳曝光量的因子。最小红斑剂量（MED）是引起肉眼可见的红斑所需的紫外线辐射剂量。
英文原文
According to the Guidelines from the American Food and Drug Administration and the International Organization for Standardization the amount of sunscreen applied when testing SPF should be 2 mg/cm2. How much of the labelled SPF is obtained when using a sunscreen is therefore dependent on the amount of sunscreen applied and whether it is spread uniformly. In reality, however, consumers apply much less sunscreen than 2 mg/cm2. External factors such as swimming, physical activity, sweating, and contact with beach sand and clothing can reduce the amount and thereby the effect. However, there are also studies on how to compensate for the insufficient sunscreen application layer obtaining increased protection.
对应中文
根据美国食品和药物管理局和国际标准化组织的指南，在测试SPF时，防晒霜的用量应为2mg/cm²。因此，使用防晒霜时会获得多少标有SPF的防晒霜取决于涂抹的防晒霜的量和涂抹是否均匀。然而，在现实中，消费者使用的防晒霜要比2mg/cm²少得多。游泳、体育活动、出汗、接触沙滩沙和衣物等外部因素都会降低用量和防晒效果。然而，也有关于如何弥补防晒应用层不足而获得更多保护的研究。
Application thickness
应用厚度
英文原文
The recommended sunscreen application thickness of 2 mg/cm2 for SPF testing is based on studies showing that this amount generates the best reproducible results with the lowest variation of test results, which are needed to ensure confidence in the efficacy classification of sunscreens. The actual amount of sunscreen applied has been shown to be about 20–50% of the amount needed to achieve the labelled SPF (4–12). A simple method used to determine application thickness has been to divide the amount (grams) of sunscreen used by the sunscreen treated skin area (cm2). In two studies sunscreens were handed over to the participants and the bottles returned and weighed every third month. Diary registrations of the skin area with sunscreen application made it possible to roughly calculate the median amount of sunscreen applied, which was 0.39 and 0.79 mg/cm2, respectively. In onceweekly evaluations children’s sunscreen use was found to be 0.48 mg/cm2, and in a 1-day study on a nude beach, in which 42 women, men and children applied their own sunscreen, the application thickness was found to be 0.5 mg/cm2 by weighing sunscreen bottles before and after an unobserved full-body sunscreen application. A holiday study with intensive sunbathing, diary registrations and daily weighing of sunscreen bottles showed that on average volunteers applied sunscreen with 0.79 mg/cm2 (men with 0.93 mg/cm2 and women with 0.66 mg/cm2). In a laboratory volunteers were instructed to apply sunscreen as usual, and the sunscreen application thickness was found to be 1 mg/cm2. This was also found in another laboratory study in which the exact area with sunscreen application was determined by adding a fluorescent to the sunscreen.
对应中文
SPF测试推荐的防晒霜涂抹厚度为2mg/cm²，其依据是研究表明，该量可产生最佳的可重复结果，且测试结果的变化最小，这是确保防晒霜功效分类的可信度所必需的。实际涂抹的防晒霜量约为达到标签SPF（4-12）所需量的20-50%。确定涂抹厚度的一种简单方法是将使用的防晒霜量（克）除以防晒霜处理的皮肤面积（cm²）。在两项研究中，每三个月将防晒霜交给参与者，并将瓶子送回称重。通过对涂抹防晒霜的皮肤面积进行日记登记，可以粗略计算出涂抹防晒霜的中位数，分别为0.39和0.79 mg/cm²。在每周一次的评估中，儿童的防晒霜使用量为0.48mg/cm²，在一个裸体海滩上进行的为期一天的研究中，42名女性、男性和儿童使用了自己的防晒霜，在未被观察到的全身防晒霜涂抹前后，称重防晒瓶发现涂抹厚度为0.5mg/cm²。一项针对密集日光浴、日记登记和每日称量防晒霜的度假研究表明，平均每位志愿者使用的防晒霜浓度为0.79mg/cm²（男性为0.93mg/cm²，女性为0.66mg/cm²）。在一个实验室里，志愿者被要求像往常一样涂防晒霜，防晒霜的厚度被发现为1mg/cm²。在另一项实验室研究中也发现了这一点，在该研究中，通过在防晒霜中添加荧光粉来确定需要涂抹防晒霜的确切区域。
Relationship between application thickness and SPF
应用厚度与SPF之间的关系
英文原文
Recently, a study testing SPF50 on 13 volunteers with an application thickness of 0.5–2 mg/cm2 proposed that the relationship between sunscreen application thickness and SPF followed a logarithmic curve. The relationship is therefore not fully determined. A study proposed that this might be due to the relationship not being uniform, as the authors tested sunscreens with both high and low SPF and found a linear doseresponse relationship for the sunscreens with low SPF (4 + 15) and an exponential dose–response relationship for the sunscreens with high SPF (30 + 55) . However, this does not correspond to previous results, as the studies that found the relationship to be linear used sunscreen with SPF25–100 (3, 16), while those studies that found the relationship to be exponential used sunscreens with either high or low SPF.
对应中文
最近，一项对13名应用厚度为0.5–2mg/cm²的志愿者进行SPF50测试的研究表明，防晒霜涂抹厚度和SPF之间的关系呈对数曲线。因此，这种关系尚未完全确定。一项研究提出，这可能是由于这种关系不一致，因为作者测试了高SPF和低SPF的防晒霜，发现低SPF(4+15)的防晒霜呈线性剂量-反应关系，高SPF(30+55)的防晒霜呈指数型剂量-反应关系。然而，这与之前的结果并不一致，因为发现两者呈线性关系的研究使用的是SPF25-100防晒霜，而那些发现这种关系是指数关系的研究使用的是高SPF或低SPF的防晒霜。
Technical factors affecting SPF
影响SPF的技术因素
英文原文
After application of a sunscreen several factors can decrease the SPF. It is recommended to wait at least 20 min before dressing after sunscreen application, but it has been shown that the negative effect of clothing is dependent on application thickness. If the sunscreen is applied with 1–2 mg/cm2 the timeinterval to clothing can be reduced to 8 min without a significant effect on SPF, while with a shorter interval the SPF will be significantly reduced. Therefore it can be difficult to apply sunscreen correctly on children on a busy morning. When the application thickness is less than 1 mg/cm2, the time interval has no impact on the SPF, probably because there is little or no sunscreen to be removed by the clothing. The effect of clothing, physical activity and bathing on SPF was tested on 19 subjects, and about 60% and 44% of the initial SPF was still left on the skin after 4 and 8 h, respectively.
对应中文
涂抹防晒霜后，有几个因素可以降低SPF。在涂抹防晒霜后，建议至少等待20分钟再进行穿衣，但事实证明，衣物的负面影响取决于涂抹厚度。如果使用1–2mg/cm²的防晒霜，则在不显著影响SPF的情况下，衣物的防晒时间间隔可缩短至8分钟，而在更短的防晒时间间隔内，SPF将显著降低。因此，在忙碌的早晨，儿童很难正确使用防晒霜。当涂抹厚度小于1mg/cm²时，时间间隔对防晒系数没有影响，可能是因为衣物很少或没有防晒霜需要去除。在19名受试者身上测试了衣物、体力活动和沐浴对SPF的影响，在4小时和8小时后，皮肤上分别残留了大约60%和44%的初始SPF。
英文原文
In a laboratory study isolated epidermis was used to test the effect of sand on 10 different sunscreens, and it was found that 15 to 59% of the sun protective effect was lost after contact with and subsequent removal of sand. The same method with isolated epidermis was used to test sunscreen products labelled waterproof or water resistant, and during four 20-min. immersions in water the two types of products lost 20–40% of their protective effect. In a recent study comprising 18 subjects the water resistance of two sunscreens was found to be significantly reduced by pretreatment of the skin with a cosmetic moisture containing lotion or cream. The reduction was registered by use of tape stripping and spectroscopic measurements before and after swimming.
对应中文
一项实验室研究用分离表皮用来测试了沙子对10种不同防晒霜的影响，研究发现，在与沙子接触并随后去除沙子后，15%至59%的防晒效果丧失了。类似方法用分离表皮测试标有防水或防水标签的防晒产品，在水中浸泡4次、每次20分钟后，这两种产品失去了20-40%的保护效果。在最近一项针对18名受试者的研究中，发现擦防晒霜前使用含水分的乳液或霜等护肤品将显著降低两种防晒霜的耐水性；游泳前后通过胶带剥离和光谱测量记录了上述耐水性减弱的具体情况。
英文原文
Another pitfall concerning sunscreen use is the potential UVR exposure before application. Unpublished data from a holiday study showed that on 48% of days with sunscreen use skin sites had received more than 0.1 SED (standard erythema dose) before sunscreen was applied, showing that it was applied outdoors. The limit of 0.1 SED was chosen to eliminate insignificant, accidental exposure. The skin sites were exposed for 100 min [range 56–392] and received in average 1.3 SED [range 0.11–9.3 SED] prior to the first application, which constituted approximately 30% of the constitutive MED [range 3%– 234%] and 22% of the total dose that day [range 1.5%–100%].
对应中文
另一个关于防晒霜使用的陷阱是涂抹前皮肤就可能暴露在紫外线下。一项假日研究中未公布的数据显示，在48%的防晒霜使用测试时间中，测试皮肤部位在涂抹防晒霜之前都接受了超过0.1SED（标准红斑剂量）的紫外线，这表明防晒霜是使用者已经在户外才开始涂抹的。选择0.1SED的限制是为了消除无关紧要的意外暴露。在第一次使用之前，皮肤部位暴露100分钟 [范围56-392]，平均接受1.3SED [范围0.11-9.3SED]，约占MED的30% [范围3%-234%]，占当天总剂量的22% [范围1.5%-100%]。
Sunscreen use related to sun exposure and sunburn
防晒霜的使用与日晒和晒伤有关
英文原文
Data from questionnaires and diaries have shown that sunscreen use is positively associated with duration of sun exposure and personal UVR doses. It has also been shown that the duration of sun exposure is positively associated with SPF and the number of sunscreen applications. Furthermore, sunburns have been found to be more frequent on days with sunscreen use, paradoxically, as sunscreen is supposed to protect against sunburn. It has been suggested that sunscreen use encourages users to extend time with intentional sun exposure, because they believe they can tolerate higher doses without sunburning. Others have suggested that people apply sunscreen, attempting to protect themselves when they know they will be exposed to high UVR doses, as well as it has been shown that sunsensitive persons are more likely to use sunscreen. These findings have been proposed as an explanation for the association between sunscreen use and sunburning and for the positive association found between sunscreen use and malignant melanoma. A meta-analysis based on 18 studies could not confirm this positive association between sunscreen use and malignant melanoma, and other epidemiological studies have shown a protective effect of sunscreens against malignant melanoma.
对应中文
调查问卷和日记中的数据表明，防晒霜的使用与日照时间和个人紫外线辐射剂量呈正相关。研究还表明，暴露在阳光下的时间与SPF和涂抹防晒霜的数量呈正相关。此外，人们还发现在使用防晒霜的日子里晒伤更频繁，这是自相矛盾的，因为防晒霜被认为可以防止晒伤。有人提出，使用防晒霜可以鼓励使用防晒霜的人故意暴露在阳光下延长时间，因为他们相信自己可以忍受更高剂量的防晒霜，而不会晒伤。其他人则提出当人们知道自己将暴露在高剂量的UVR下时、将更有可能涂抹防晒霜以试图保护自己；而且有研究表明，对太阳敏感的人更有可能使用防晒霜。这些发现有被建议用来解释防晒霜的使用和晒伤之间的联系，以及防晒霜的使用和恶性黑色素瘤之间的正相关。一项基于18项研究的荟萃分析没有发现使用防晒霜与恶性黑色素瘤之间的正相关关系，而其他流行病学研究则显示防晒霜对恶性黑色素瘤有保护作用。
CONCLUSION
结论
英文原文
It is clear from the studies presented in this review that there is a discrepancy between the amount of sunscreen applied during testing and in reality. The amount of 2 mg/ cm2 is used for SPF testing because it gives more reproducible results than a smaller amount of 0.5–1.0 mg/cm2 as is applied in real life. The relationship between the sunscreen application thickness and the SPF is probably product dependant and may not always be fully exponential . When the reality of sunscreen use is taken into consideration, current sunscreen labelling is seen to overrate the protective effect of sunscreens, which may possibly mislead consumers to feel safe to extend sun exposure. The effect of education on sunscreen application thickness was studied, but it only resulted in sunscreen layers of 0.8–1.13 mg/cm2. In vivo studies showed that early reapplication can increase the sunscreen layer to 0.95–2.01 mg/cm2. Other studies showed that very high SPF (70–100) may compensate for insufficient application thickness.
对应中文
从这篇综述中介绍的研究可以清楚地看出，在测试过程中使用的防晒霜的量与现实中的防晒霜用量之间存在着差异。SPF试验使用2 mg/cm²是因为它比实际应用的0.5-1.0 mg/cm²的小剂量提供了更多的重复性结果。遮阳板应用厚度与SPF之间的关系可能与产品有关，并不总是完全呈指数关系。当考虑到防晒霜使用的实际情况时，目前的防晒霜标签被认为高估了防晒霜的保护作用，这可能会误导消费者感到延长防晒时间是安全的。研究了教育对防晒霜涂抹厚度的影响，但只产生了0.8-1.13 mg/cm²的防晒层。体内研究表明早期重复使用可使防晒层增加到0.95-2.01mg/cm²。其他研究表明，非常高的SPF(70-100)可以弥补涂抹厚度的不足。
英文原文
Other major pitfalls in sunscreen use are ‘missing areas’ and UVR exposure before sunscreen application. In a holiday study sunscreen was not applied until outdoors in 48% of the cases and these skin sites received approximately 30% of the constitutive MED [range 3%– 234%] prior to sunscreen application.
对应中文
使用防晒霜的其他主要缺陷是“缺失区域”和涂抹防晒霜前的紫外线照射。在一项假日研究中，48%的人直到户外才涂抹防晒霜，这些皮肤部位在涂抹防晒霜之前接受了大约30%的结构性MED [范围为3%-234%]。
英文原文
Educating the entire population on how to apply sunscreen or increasing the amount of sunscreen by a factor of 2 to 4 may not be realistic, whereas reapplication seems to be a more realistic way to obtain a thicker sunscreen layer with increased protection. Using very high SPF may be recommended, but the products are typically more difficult to apply uniformly.
对应中文
教育所有人如何涂抹防晒霜或将防晒霜的用量增加2到4倍可能是不现实的，而重复使用似乎是获得更厚的防晒层和增强保护的更现实的方法。可以推荐使用SPF值很高的产品，但通常情况下，产品很难均匀涂抹。
英文原文
We therefore suggest a simple teaching strategy: (1) Apply before sun exposure and (2) Reapply once within 1h.
对应中文
因此，我们建议一个简单的教学策略：(1)在阳光照射前涂抹，(2)在1小时内重新涂抹一次。
REFERENCES
1.Petersen, B. and H. C. Wulf (2014). “Application of sunscreen–theory and reality.” Photodermatol Photoimmunol Photomed 30(2-3): 96-101.