Testing Sunscreen Effectiveness

Abstract

Objective

The goal of this project is to measure the effectiveness of different sunscreen products for blocking ultraviolet-A (UVB) and ultraviolet-B (UVB) rays from sunlight.

Credits

Andrew Olson, Ph.D., Science Buddies

Sources

This project is based on:

• Roberts, S.H., 2005. "Is Sunscreen SPF for Real?" California State Science Fair Project Abstract [accessed October 12, 2006] http://www.usc.edu/CSSF/History/2005/Projects/J1127.pdf.

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Introduction

Ultraviolet (UV) light is invisible to our eyes, and has higher energy than visible light. "When considering the effect of UV radiation on human health and the environment, the range of UV wavelengths is often subdivided into UVA (400–315 nm), also called Long Wave or 'blacklight'; UVB (315–280 nm), also called Medium Wave; and UVC (<280 2006)

Click here to watch a video of this sunscreen investigation, produced by DragonflyTV and presented by pbskidsgo.org

The following facts link sunlight exposure to skin cancer:

• "Most skin cancer occurs in areas of skin most heavily exposed to sunlight (ears, forehead, arms, etc).
• "Skin cancer among people who are sensitive to sunlight is more common in regions with stronger sunlight.
• "People with genetic diseases that make them more sensitive to sunlight have a greater chance of developing skin cancer.
• "Studies show that ultraviolet radiation similar to sunlight causes skin cancer in animals." (CCOHS, 2005)

Sun lotions are supposed to protect the skin from harmful UV radiation. Are they effective in blocking UV light? In this project you will use a UV detector to find out.

Would you like to watch a video about testing different SPF levels in sunscreens? Click on the image to see the DragonflyTV video "Sunscreen by Aaron and Justin".

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:

• ultraviolet (UV) light
• UVA
• UVB
• UV Index
• sun protection factor (SPF)
• skin cancer:
  • basal cell cancer
  • squamous cell cancer
  • malignant melanoma

Questions

• What is the difference between UVA, UVB, and UVC radiation?
• What happens to UVC radiation from the sun in the earth's atmosphere?

Bibliography

• This Wikipedia article discusses ultraviolet light:
  Wikipedia contributors, 2006. "Ultraviolet," Wikipedia, The Free Encyclopedia [accessed October 12, 2006] http://en.wikipedia.org/w/index.php?title=Ultraviolet&oldid=76387342.
• This webpage from the Canadian Centre for Occupational Health and Safety will give you an introduction to the effects of UV light on skin:
  CCOHS, 2005. "OSH Answers: Skin Cancer and Sunlight," Canadian Centre for Occupational Health and Safety [accessed October 12, 2006] http://www.ccohs.ca/oshanswers/diseases/skin_cancer.html.
• This webpage from Dragonfly TV has a video showing how two kids in Southern California carried out their sunscreen project:
  TPT. (2007). Sunscreen by Aaron and Justin. DragonflyTV, Twin Cities Public Television. Retrieved July 1, 2008 from http://pbskids.org/dragonflytv/show/sunscreen.html

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• a UV monitor, like this one from Amazon.com, that displays the UV Index
• sun lotions with different SPF (sun protection factor) ratings (e.g., SPF 8, 15, 30, 50),
• plastic wrap,
• a day with bright sunshine.

Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed. However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies receives no consideration, financial or otherwise, from suppliers for these listings. (The sole exception is any Amazon.com link.) If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

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Experimental Procedure

1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
2. The UV monitor used in this project will have to be ordered online, so plan ahead and get it early so that you have time to complete your project.
3. Make your measurements on a bright sunny day.
4. Tear off a piece of plastic wrap and hold it over the detector. Make sure that only the plastic is between the sun and the detector—avoid casting a shadow on the detector. Record the UV Index reading. This will be your control reading, and will be a baseline for you to compare the other readings to and see if they increase or decrease.
5. Cover the plastic wrap with a thin, uniform layer of sun lotion #1. Allow the lotion to dry. Hold this over the detector and record the UV Index reading.
6. Subtract the blank plastic reading from the plastic+sun lotion reading. The result shows how much the sun lotion reduced the UV Index.
7. Repeat the measurements for each sun lotion you are testing.
8. Once you have gone through all of the lotions, go back and repeat the measurements twice more.
9. Calculate the average UV Index reduction for each sun lotion by adding the values from your three independent measurements and dividing the result by three.
10. Compare the UV Index reduction for each SPF. Which sun lotion is most effective at blocking UV? Are the results consistent with the SPF rating for each lotion?

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Variations

• Compare the UV Index on cloudy vs. sunny days. Do you still need sun lotion on cloudy days?
• Compare the amount of UV Index at different times of the day (without cloud cover).
• If you live near mountains, you can compare the UV Index. Take a drive with your family on a sunny day and take measurements at different altitudes. Take several measurements at each altitude, noting the conditions for each measurement. Remember to record the time of day for each measurement. Compare measurements taken at high altitude with measurements taken at the same time of day at lower altitude (or vice versa). How does UV Index change with altitude?
• For an experiment using short-wave UV (UVC) light to kill bacteria, see the Science Buddies project Death Rays: What Duration of Ultraviolet Exposure Kills Bacteria?.

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Related Links

• Science Fair Project Guide
• Other Ideas Like This
• Materials Science Project Ideas
• My Favorites

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