夏日炙熱的陽光不僅會讓皮膚變黑變粗糙，經常暴曬還會導致皮膚癌。正確地使用防曬霜可以防止太陽紫外線對皮膚的傷害。一起來看看防曬霜的正確用法。

Wearing sunscreen is widely acknowledged as being one of the best things we can do for our health. More than 80% of melanoma skin cancer cases are caused by sunburn – and this number is rising year on year. There are an estimated 1.5 million new cases of skin cancer globally each year, with this figure expected to rise by 50% by 2040.

涂抹防曬霜被廣泛認為是我們為健康所能做的最好的事情之一。超過80%的黑色素瘤皮膚癌病例是由曬傷引起的——這個數字每年都在上升。全球每年大約有150萬例新發皮膚癌病例，預計到2040年這個數字將增加50%。

Despite these stark facts and repeated public health warnings about the risks of sun exposure, there's a lot of confusion around how, and when, to apply sunscreen.

盡管關于日曬風險有這些嚴酷的事實和反復的公共衛生警告，但人們關于如何以及何時涂抹防曬霜仍存在很多困惑。

Why do we need to protect our skin from the sun?

我們為什么需要保護皮膚免受陽光傷害？

When we're exposed to the sun, UV radiation damages the DNA, proteins and other molecules found within our skin cells, says Richard Gallo, professor of medicine at University of California.

加州大學醫學教授理查德·加洛指出，當我們暴露在陽光下時，紫外線輻射會損害我們皮膚細胞內的DNA、蛋白質和其他分子。

In moderate amounts, exposure to UV radiation from sunlight helps our skin cells to generate vitamin D. But as we expose our skin to more sunlight, it tries to protect itself by tanning through the production of melanin, Gallo says. "If the exposure is too high, the skin can't protect itself and you get a burn," he says.

加洛指出，適量接觸陽光中的紫外線輻射有助于我們的皮膚細胞生成維生素D。但當我們的皮膚暴露在更多的陽光下時，皮膚會通過產生黑色素來努力進行自我防護。他說：“如果被過度暴曬，皮膚就無法保護自己，你就會被曬傷。”

This can lead to DNA damage in our cells, which can cause premature ageing, and can increase the risk of developing skin cancer, Gallo says.

加洛說，這可能導致我們細胞中的DNA損傷，從而導致過早老化，并增加患皮膚癌的風險。

Exposure to UV radiation is the main cause of the most common forms of skin cancer.

接觸紫外線輻射是引發最常見的皮膚癌的主要因素。

One 2018 study found that after sunscreen is applied, some UV protection kicks in immediately – though it takes around 10 minutes for this to become stable. However, experts usually recommend that people apply sunscreen 20-30 minutes before sun exposure to allow time for it to absorb into the skin. It might be wise to apply it twice, since studies show that most people tend to underapply sunscreen.

2018年的一項研究發現，在涂抹防曬霜后，會立刻產生一部分對紫外線的防護作用——盡管防護效果需要大約10分鐘才能穩定。然而，專家通常建議人們在日曬前20-30分鐘涂抹防曬霜，以便留出時間讓它被皮膚吸收。可能明智的做法是涂抹兩次，因為研究表明大多數人通常涂抹的量都不足。

In one study, researchers asked 31 participants to apply sunscreen in a lab under black light, and found that applying it twice reduced the surface area of skin that they missed the first time around.

在一項研究中，研究人員要求31名參與者在實驗室的黑光燈下涂抹防曬霜，發現涂抹兩次減少了他們第一次遺漏的皮膚表面積。

Scientists also advise reapplying sunscreen after sweating, being immersed in water, or if our skin has rubbed up against clothing or sand.

科學家還建議在出汗、浸泡在水中或皮膚與衣物或沙子摩擦后重新涂抹防曬霜。

It's also important to not mix sunscreen with other skin products, such as moisturiser, says Richard Blackburn, professor of sustainable materials at the University of Leeds' school of design. This is because many sunscreens that contain metal nanoparticles like zinc oxide may be less effective because of how these ingredients react with other ingredients.

利茲大學設計學院可持續材料學教授理查德·布萊克本說，不要將防曬霜與潤膚露等其他皮膚產品混用，這一點也很重要。這是因為許多含有金屬納米顆粒（比如氧化鋅）的防曬霜可能因為這些成分與其他護膚品成分的反應而導致效果降低。

Blackburn advises against mixing different brands of sunscreen, or mixing a sunscreen with other skin products, in case some of their ingredients are incompatible with each other.

布萊克本建議，不要混用不同品牌的防曬霜，或將防曬霜與其他護膚產品混用，以防它們的一些成分彼此不相容。

英文來源：BBC

翻譯&編輯：丹妮

審校：齊磊、高琳琳