Written by Rhys Finnick
Rhys is a Science Facilitator at Science World, a comedian and one half of the wildly popular accordion-based Weezer cover band, Squeezer. His scientific interests include wondering why water is wet and reading popular science books in public so people will think he's as sharp as his Science World colleagues. In his spare time, Rhys enjoys napping, eating candy, and watching Dr. Phil help solve the world's problems one step at a time.


Created date

Monday, July 23, 2018 - 4:43pm

How Sunscreen Works

It’s strange to think that one of the things that created life, something that we all depend on to survive would kill us if given the chance. No, I’m not talking about water (although it can also be hazardous if you can’t swim). I am talking about the sun and it’s searing, scorching rays of ultraviolet light.

What can you do to protect yourself from this great ball of fire?

Vitamin D & UV & You

The first thing you could do is never go outside again. As Russian police learned a few years ago, when they discovered a cult living underground (some since birth), humans can live without sunlight, so long as they have a proper diet with enough Vitamin D. It seems a bit extreme, but hey, you do you.

Another thing you could do is throw all caution to the wind and take your chances out in the sun. Luckily, your body can turn some of the sun’s energy into Vitamin D. After sunlight makes its eight-and-a-half minute journey to earth, much of its radiation is absorbed by the ozone layer and atmosphere. What’s left, a combination of invisible Ultraviolet A (UVA) and Ultraviolet B (UVB) solar rays, penetrates your skin, and the UVB reacts with a chemical near the surface of your skin to dramatically improve Vitamin D production. Depending on how light or dark your skin is, your body only needs between ten to thirty minutes of sunshine a day to get it’s daily fill of Vitamin D.

However, if you want to spend more than ten minutes outside at a time, a third idea would be to go outside wearing sunscreen. Let’s explore that option.

Blocks and Screens

There are two different types of sunscreen on the market: physical sunscreens  (also called sunblock), which block and deflect the UV rays from entering your skin, and chemical sunscreens, which contain organic chemicals that react with the UV radiation to produce heat energy that floats away from your skin. Neither of these should be confused with suntan lotion, used with indoor tanning beds to boost the tanning effect. Both chemical and physical sunscreens work well, but the most important things to look for are broad-spectrum sunscreens (these protect against both UVA & UVB radiation) and something with the right amount of SPF (Sun Protection Factor).

How does SPF work? You’ve probably seen sunscreen bottles with different numbers of SPF on them, but what do they mean? Is SPF 15 sunscreen just for fifteen year olds? Does SPF 30 sunscreen work for only a half hour? Will 50 Cent be mad at you for using SPF 50 sunscreen?

Ya Best Protect Ya Neck

The Sun Protection Factor number on your sunscreen bottle determines what fraction of the damaging UV rays will make it to your skin (e.g. SPF 30 sunscreen will only allow 1/30th of sunburn-causing radiation to get you. A way you can apply the SPF number to yourself is to multiply the SPF by the amount of time it normally takes you to get a sunburn without sunscreen (i.e. when your skin starts to look like an active volcano) and you should be safe for that many minutes. For instance, I have very fair skin so I burn like a snow cone in Phoenix melts in about ten minutes, so if I used SPF 30 sunscreen, I would theoretically be safe from sunburn for about five hours. Or:

10 minutes till Burnination           X             SPF 30                   =             300 minutes or five hours

That being said, it’s important to reapply your sunscreen every couple of hours as UV ray frequency fluctuates in intensity throughout the day and you will likely sweat and/or swim some of it off doing your thing out in nature. Dermatologists warn that most sunscreen users apply only half the amount they should (around two milligrams of thickness), so be as liberal as possible with that white liquid gold. Though no sunscreen can thwart 100% of the suns UV rays, any sunscreen with an SPF of 15 or higher will protect you from upwards of 90% of them (SPF 15/30/50 block 93%/97%/98% of harmful UVB respectively).

Be Cool, Wear Sunscreen

After a slow start to the sunshine season in Vancouver, temperatures have started picking up in our south-western part of the province, so there’s no better time than now to start being conscious of your sunscreen use. Skin problems stemming from the sun range from the aesthetics of looking older (like half of this retired trucker’s face – the side that faced the window) to the dangers of cancers like melanoma.

Don’t let this be you.

Want to know more about sunlight? Visit our newly re-opened BodyWorks Gallery, where you can view your skin through the UV camera in the skin-scanner. Also, check out our resources page for a cool UV Bead activity (& a whole lot more).

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