Sunburns on Cloudy Days

How It's Possible to Get a Sunburn on Cloudy Days

Sabrina Schrope

Cosmetic Chemist, Owner of Vitamin You

 

After our last article investigating how sunscreens work, there's a new question being asked: How is it possible to get a sunburn even if it's cloudy?

Here, I've provided a simple answer, infographic, and the deeper science for your learning preference!

 

Simple Answer:

As we talked about in our last article, there are three different types of UV rays: A, B, & C. UVA mostly causes DNA damage, UVB mostly causes sunburns, and UVC rays currently do not pass beyond the ozone layer. 

Unfortunately, according to Cancer Research UK, over 90% of these UVA and UVB rays can still pass through light cloud coverage.1

A better way to gauge your UV exposure risk is by looking up your local zipcode's daily UV Index. That is, a scale from 1-11+ on how severe your UV risk is. In the USA, the Environmental Protection Agency (EPA) offers a free online took to look up by your zipcode:2

https://www.epa.gov/sunsafety/uv-index-1

Another special feature about UV rays is that they can scatter and reflect off snow, water, and sand. Even if you have cloud coverage where you are, there is also the chance of these large bodies of UV reflective material to expose you to UV rays.1

Moreover, people who live closer to the equator will have stronger UV exposure than those who live farther out.1

 

An Infographic:

A visual representation of UV rays from the sun, passing the ozone layer, getting reflected and scattered by clouds, then hitting earth

As shown above, the ozone layer is able to absorb most of the UVC and UVB rays. Once the UVB and UVA rays hit the clouds, some are reflected and the rest are scattered forward.

 

An In-Depth Explanation:

Ultraviolet radiation (UVR) is energy that moves in a wave formation. The UVR energy from the sun is strong enough to reach Earth and into its Ozone layer, where most, if not all, of the UVC rays will get caught in reactions with oxygen molecules. UVB is also mostly absorbed in these reactions, but plenty still make it through with UVA rays into the lower atmospheric layers. 

Clouds are made of water, gas, and impurities like salt and dust. When both visible light and UV waves hit clouds the energy is reflected and scattered. Visually, some light is still seen on cloudy days due to the passing of visible light. In the same respect, unseen UV waves are also passed through the clouds. According to the Cancer Research UK, over 90% of UVA and UVB rays can still pass through light cloud coverage. As stated before, these two UV rays can cause DNA damage and UVB rays specifically can cause sunburn.1

Practice sun safety and wear sunscreen!

 

Citations:

The UV Index and Sunburn Risk. June 2021. Cancer Research UK. <https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/sun-uv-and-cancer/the-uv-index-and-sunburn-risk>.

UV Index. May 2022. EPA. <https://www.epa.gov/sunsafety/uv-index-1>.

 

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