How effective is your sunscreen?

Author: Maddie Van Beek

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It has been a HOT week in Fargo, North Dakota! Almost every day the temperature has reached 90 degrees fahrenheit. When the sun is out (and even when it’s not) it’s very important to protect your skin! While the sun gives us many benefits such as light and Vitamin D, it can also be very harsh on your skin.


Have you ever gotten a tan line from being out in the sun? When you’re exposed to Ultraviolet rays from the sun, your skin produces melanin. That melanin is a pigment that makes your skin darker. In the picture below, you can see the difference between the area of this person’s arm that was exposed to the sun and the area that was covered. The exposed area has produced more melanin and thus is tanner. ​

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While getting tan isn’t a bad thing, you want to protect your skin from getting burned. When your skin gets red rather than tan, it’s been burned. While getting burned once or twice isn’t the end of the world, continued sun burns could cause skin damage or increase your risk of skin cancer. 


How can you protect your skin? 
You can be proactive and avoid getting burned by wearing protective clothing that has a high UPF rating. You can also apply sunscreen to protect your skin, but make sure you do this BEFORE you go outside and reapply throughout the day. The Skin Cancer Foundation recommends that you reapply every two hours, just to be safe. 


What’s the difference between SPF and UPF? 
UPF is the rating for clothing that protects you from the sun while SPF is the rating system for sunscreen. SPF stands for Sun Protection Factor while UPF stands for Ultraviolet Protection Factor. The SPF rating measures the amount of time it takes for your skin to redden in the sunlight, while UPF measures the amount of the sun’s UV rays that can penetrate the clothing. If a shirt has a UPF of 35, then 1/35th of the UV rays are making it through the fabric. 


How does sunscreen block the sun? 
There are a few different types of sunscreen, but all sunscreen does at least one of two things. It either contains chemical compounds that absorb the UV light from the sun, or it contains ingredients such as zinc oxide or titanium dioxide that act as a block that reflects the UV light from your skin. 


Check out this link to learn more about the science of sunscreen: ​

The Science of Sunscreen

Now that you know more about sun protection, let’s get started on our activity! You are going to actually test the effectiveness of sunscreen. Don’t test this out on your skin! We are going to use special sun-sensitive paper to test how well different sunscreens work. 


Test the Effectiveness of Sunscreen


YOU WILL NEED: 

• Sunscreen of different SPF ratings
• Sun-sensitive paper (You can buy on Amazon here: https://www.amazon.com/Nature-Print-Paper-inch-Pack/dp/B0042SSSVE) 
• Ziplock bags
• Tablespoon
• A sunny day

Here’s what to do! 

1. Make sure you start your experiment inside. You are using special paper that reacts to the sunlight, so you need to keep the paper out of the sun until it’s testing time. 
2. Gather sunscreens of various SPF ratings. For example, you could choose 15 SPF, 30 SPF, 50 SPF and 70 SPF. 
3. Remove a piece of sun-sensitive paper and write “control” on the back. Next, place it inside a ziplock bag. This piece of paper gets no treatment from any sunscreen. 
4. On the back of the second sheet, write “15 SPF” and place it inside a ziplock bag. Smear a tablespoon of 15 SPF sunscreen all over the surface of the bag. 
5. On the back of the third sheet, write “30 SPF” and place inside a ziplock bag. Smear a tablespoon of 30 SPF sunscreen all over the surface of the bag. 
6. Continue with this process until you have created a bag to test each variety of sunscreen. 
7. Carry each bag outside and set in the sun with the sunscreen-smeared side facing up. 
8. After about five minutes, you can go get your bags and bring them inside. Submerge each bag in a tub of water and rinse off the sunscreen. 
9. Analyze each piece of paper. The white areas of the paper were blocked by the sunscreen, while the blue areas of paper were not. What do you notice? Do all the sheets look the same? Did a higher SPF rating better protect your paper? Write down your observations. 

Now you know why wearing a high SPF sunscreen is so important! 


Extensions:

1. Some people actually forgo sunscreen and use tanning oil or baby oil to enhance their tan. Test out a few different oils to see what happens. Do any of them provide any protection? 
2. Are some sunscreen brands better than others? Choose three different brands of the same SPF rating and compare their effectiveness. 
3. Clothing also has some sun protection, but some fabrics block more sun than others. Try putting the paper inside a few different items of clothing and set in the sun to test how well clothing could protect you. 

References:

• Skin Cancer Foundation, 2014. Get in on the trend. http://www.skincancer.org/prevention/sun-protection/clothing/get-in-on-the-trend
  
• Grifantini, 2010. How does sunscreen work? http://www.livescience.com/32666-how-does-sunscreen-work.html
• 2016. Sunscreen. https://en.wikipedia.org/wiki/Sunscreen
• Mauk, 2013. Why does the body tan? http://www.livescience.com/32493-why-does-the-body-tan.html

Image credits in order of appearance: 

• Hudson, Dawn. Sunglasses and lotion clipart. Uploaded from publicdomainpictures.net on 7/24/2016. http://www.publicdomainpictures.net/view-image.php?image=79912&picture=sunglasses-and-lotion-clipart File released into public domain. 
  
• Onetwo1, 2007. Tanned arm. Uploaded from Wikimedia Commons on 7/24/2016. https://upload.wikimedia.org/wikipedia/commons/thumb/6/65/Skin_tanning.JPG/1280px-Skin_tanning.JPG File used in accordance with the Creative Commons Attribution-Share Alike 3.0 Unported license.