Does a generic sunscreen absorb UV light as well as a name-brand sunscreen? Does expired sunscreen still work?

These are two questions that Douglas Harris, PhD, asks his students at Utah State University to answer by completing the “Absorption Spectrum of Active Ingredients in Sunscreens” investigation. Harris and a colleague developed this beginning-of-the-semester experiment to teach students how to perform dilutions, an important process used in later biochemistry experiments, as well as how to accurately analyze data.

Investigating with the Spectrophotometer

In the experiment, students extract the active ingredients from two different sunscreens using isopropyl alcohol and then create a 1:10 dilution to test. Students collect and record their spectra for these active ingredients using the Vernier UV-VIS Spectrophotometer and compare each for UVA and UVB radiation exposure protection.

“After using Vernier technology in some of my other courses, I saw how powerful it could be in this investigation,” said Harris. “The UV-VIS Spectrophotometer helps students easily and accurately collect data and measure the absorbance spectra of their samples.”

Through their data analysis, students found that a sunscreen’s effectiveness depends on the brand, but generic brands sometimes actually outperformed the name-brand sunscreens. In addition, they found that the expired sunscreen often effectively absorbed UV radiation as well as the unexpired sunscreen. When testing a specific brand of sunscreen, students found that the absorption of the 100 SPF sunscreen was approximately double the absorption of the 50 SPF sunscreen.

“The students can see all of these findings in real time using the spectrophotometer,” said Harris.

Consistent Results in Chemistry

For more than 15 years, Vernier technology has been an integral part of Harris’ courses to highlight key chemistry concepts, including teaching students about amino acid titrations using pH sensors and studying reaction kinetics of nail polish remover with dilute sodium hydroxide using conductivity probes.

“The use of technology is second nature to today’s students,” said Harris. “The Vernier data-collection technology is no exception—it’s intuitive for them to use technology to gather the data they need.”

“Technology can be frustrating if it does not produce consistent results,” continued Harris. “Through the years, Vernier technology has always provided my students with reliable and accurate data, plus the company has always offered great support with questions.”

Download this investigation, “Absorption Spectrum of Active Ingredients in Sunscreens.”


About the Educator

Douglas Harris, PhD
Utah State University
Logan, UT

Douglas Harris has worked as a lecturer for Utah State University’s Department of Chemistry and Biochemistry for 17 years. He received his doctorate in biochemistry and currently supervises the department’s introductory biochemistry teaching labs.