We Tested If We Really Need To Apply Sunscreen Indoors & On Cloudy Days

by Bettina Miski on Apr 16, 2023

Do i really have to wear spf every day?

Although we keep hearing how important it is to wear sunscreen every single day, people still wonder whether it is really necessary or not on cloudy, rainy days, and even indoors. During these days, the sun might not be present. But how about the UV? Kasper, our „Beauty Facts Unboxing” host did her research to find the answers to all these questions. She took her wavelength measurement tool and tested the UV indoors, in front of different windows, and outdoors under different weather conditions.

Do I Really Have To Wear Sunscreen Indoors, Or In The Car?

window with no uv vlocking function

During our tests on sunny days, the UV waves went as high as 1100-1800 outdoors, while even in the shade the machine measured around 2-300. But how much protection can a window or your choice of transportation give you? In front of windows with no UV blocking function, the UV index still ranged around 120-130. And while we were on the bus, the test had similar results to outdoor conditions in the shade.


"How about windows that were specifically built to block UV?" 

While the result is significantly lower (around 16), some rays still make it through the glass. Therefore our answer is yes. Yes, you should still wear sunscreen indoors and in vehicles. We all tend to be a bit lazier with our skincare on days like these, but building a lightweight routine will feel amazing on your skin! The Safe Inside & Outside Set contains a pore cleansing foam, a pack of calming sheet masks, and the Kahi Aqua Balm that makes even reapplying sunscreen pretty convenient. 

On top of these three products, you can choose either Mixsoon’s Centella Asiatica Sun Cream or the Thank You Farmer Safe Sun Fluid AGE 0880 as part of the set. 

Do I Have To Wear Sunscreen On Cloudy And Rainy Days? 

uv index measurements in rainy and cloudy days

Okay, we know the answer to home office days and lazy weekends. But what if the sun’s not even out? Do clouds or rainfall cover up the harmful UV rays? UV rays are actually divided into three types depending on their wavelength. UVC has the shortest wavelength and is mostly blocked by the ozone layer. Which is probably why you heard the least about it.

uv rays

While UVB and UVA might sound more familiar. UVB affects the skin's outer layer, causing sunburn. Its waves are less likely to make it through a cloudy skyline which is why we don’t tend to tan or burn on days when the Sun is hiding behind the cloud. The SPF measurement on your sunscreen indicates its protection against UVB rays.

uv-b and uv-a rays

On the other hand, since UVA has the longest wavelength, it can penetrate clouds, windows, and even light clothing. These UV rays affect the skin's dermis and damage it from deep within, also causing premature aging. The PA rating on the sunscreen bottle signifies the protection level against UVA rays. 

If you want to ensure high protection and prevent premature signs of aging, you can build a fitting routine with the Well Aging SPF Set

Kasper’s test showed that even on cloudy days some of these rays are just as present as on sunny days. Although the indoor UV levels show a lot lower result. On a cloudy day, next to a (non-UV protective) window, we still measured 57. But on a day with heavy rain, the number came out as zero for the only time in our tests without UV-blocking glass. But only indoors! Outdoors still showed the presence of UV with a wavelength of 55 on a rainy day.


So in conclusion, Kasper unboxed the fact that our skin is barely ever safe from UV rays. The research proved that the answer once again is the same, yes. Yes, you should wear sunscreen even on a cloudy and rainy day. But with our tips, it will be easy to make applying SPF a part of your daily routine. And forgetting it will never be a problem again.

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