The Sunscreen SPF Test
Most kids know that sunscreen is a staple in the summer and on vacation, but with so many different Sun Protection Factor (SPF) levels, have you ever wondered which works the best to keep out the sun's harmful ultraviolet (UV) rays? Aaron and Justin, science fair project contributors on PBS KIDS GO DragonflyTV, decided to find out.
How Sunscreen Works
Sunscreen is made from both inorganic and organic components. The inorganic ingredients reflect/deflect the harmful ultraviolet radiation from the skin's surface, while the organic components work to absorb UV waves, dissipating them as heat.
Sun Protection Factor
Ultraviolet radiation can be broken down into three types of wavelengths including UV-A, UV-B, and UV-C. It is the UV-A and UV-B rays that are the most troubling; both can cause sunburn and other skin problems like cancer, etc. The Sun Protection Factor (SPF) of sunscreen measures how effectively the sunscreen limits skin exposure to damaging UV-B rays. The higher the number, the more protection promised. [NOTE: SPF does not measure protection against the damage of UV-A rays.]
Aaron and Justin decided to test three different levels of SPF - including 4, 15, and 30 - along with both olive oil and cooking shortening (just for fun!) on sun sensitive water bottles. After slathering up the bottles, the boys placed them in a sunny location for eight minutes and rated the change of each bottle on a scale of one to five - five being most colored/least protection/"burnt" and one being least colored/most protection.
If you can't get your hands on sun sensitive water bottles, you might also consider using sun sensitive paper and plastic bags. To use this method, follow this link to Steve Spangler Science.
To view the rest of Aaron and Justin's project including a project video, procedure, conclusions, and extensions, be sure to visit their project page at PBS KIDS GO!