Every year during the summer, millions upon millions of people squeeze out sunscreen on the beach to smear across their body, confident that they are protected from the sun. Most of the time, they are. But ask any dermatologist what infuriates them most, and 80% of the time sunscreen myths would be in their top ten. People think that you only need to apply it once for the whole day. Others think that on a cloudy day you could skip it.
However, none of that is actually how sunscreen works. So let me explain it to you, starting with what you’re defending from, to the chemistry of the product.
UVA VS. UVB
Everyday, the sun releases two types of ultraviolet radiation onto your skin. UVA (315-400 nm) and UVB (280-315 nm), with UVB being the cause behind both sunburn and skin cancer. In fact the SPF value that is seen on sunscreen bottles, is the measure of UVB that it can block. While UVA can cause early aging and increase chances of cancer since it can penetrate deep into the skin. It can also penetrate window glass, which explains why almost 95% of UV radiation on the ground level is UVA. Have no fear, though, your sunscreen is designed to block both forms of radiation, which is actually what “broad spectrum” label means.
Hearing this, one might assume that the higher SPF value that you have the better your sunscreen. But in reality SPF measures the UVB that the sunscreen can block, while the SPF and real world protection relationship isn’t as linear. Contrary to popular belief SPF isn’t twice as protective as SPF 50, in fact it’s only one percent higher. The real protectiveness isn’t relying upon the higher SPF but rather how much you apply.
As measured results from the labs are based on 2 milligrams per square centimeter of skin. An average human male would have around 16,000 to 18,000 cm² of skin, resulting in the requirement of 32,000 to 36,000 milligrams of sunscreen to receive the proper protection advertised. That’s almost the same amount needed to fill a shot glass, and yet people apply around a quarter of that amount which would reduce its effects. As if you were to do that with SPF 50, it would block the same amount of UVB as SPF 10. So when you’re applying sunscreen, make sure to use a lot more than you think to maximize your effects.
Composition Of Sunscreen
In today’s world there are two main types of sunscreen, mineral and chemical sunscreens. They are obviously composed of different materials but do you know what those materials are? Mineral sunscreens often use titanium dioxide or zinc oxide as active ingredients. Don’t be frightened by their names, they are both recognized as minerals that are safe and effective according to the FDA. The way that they work is by sitting on top of the skin, where they absorb the UV radiation and convert some of it into heat. These kinds of sunscreens work instantaneously after applying, protecting you from both UVA and UVB, and don’t often irritate sensitive skin. The downside is that it’s the source of the infamous white smear on your body on the beach.
Although the newer modern formula have improved by almost eliminating it from appearing. Then there are chemical sunscreens that use oxybenzone or avobenzone which are organic molecules that sink into your upper skin layer and absorb UV radiation. Similar to mineral sunscreen, they release it as heat before it can reach and damage your DNA. But they are different, since they leave no white smear at all since their creation and they need 15 to 20 minutes after applying to activate. However since they can degrade in the sunlight, you need to reapply it once every two hours to block off the UV radiation properly for the whole day.