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Sunscreen by Aaron and Justin

In Southern California, we can't help but catch rays! We're outside a lot, so we slather on the sunscreen. With all of the SPF (Sun Protection Factor) numbers available, we want to know: What SPF lotion really works best at keeping out the sun's harmful UV rays?

What did we do?
We found sunscreens with three levels of SPF: 4, 15 and 30. Just for fun, we also tested regular cooking shortening and olive oil to see how they blocked the rays. To test each lotion, we slapped the lotions on a water bottle made of a special kind of plastic that turns color in the sun. Then we exposed the lotion-covered bottle to the rays for eight minutes. That's about the amount of time it takes for a fair-skinned person to start burning. Finally, we rated the color of the water bottle on a scale of 1-5, with 5 showing the most color or "burning" and 1 showing the least color.

What did we find out?
SPF 4 got a rating of 5, SPF 15 was rated a 1, SPF 30 was also rated a 1. Shortening was rated a 5 and olive oil was rated a 4. SPF 4 doesn't do much at all, while 15 and 30 do about the same. The cooking fats didn't do much at all, which showed us that even though the shortening is thick and opaque, it sure doesn't block UV rays.

What can you do?
  • Does the kind or color of the fabric you're wearing make a difference blocking the sun? Try the above experiment by cloaking a sun-sensitive water bottle with fabrics in a variety of colors and materials (cotton, polyester or light wool). What differences do you find? Which fabric fares the best as a sunscreen? Record your results.
  • How does the time of day affect how much UV you get? Try the sunscreen experiment at different times of day, and see what colors the bottle turn.
  • Use this human body investigation as a science fair project idea for your elementary or middle school science fair! Then tell us about it!
more resources
More on Ultraviolet Light

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