Testing Sunscreen Effectiveness
AbstractHow effective are different sunscreen products at blocking harmful UV radiation from sunlight? This project shows you how to use a UV detector to find out.
Andrew Olson, Ph.D., Science Buddies
This project is based on:
- Roberts, S.H., 2005. Is Sunscreen SPF for Real? California State Science Fair Project Abstract. Retrieved October 12, 2006.
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.
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 nm), also called Short Wave or 'germicidal'." (Wikipedia, 2006)
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
- UV Index
- Sun protection factor (SPF)
- Skin cancer:
- Basal cell cancer
- Squamous cell cancer
- Malignant melanoma
- What is the difference between UVA, UVB, and UVC radiation?
- What happens to UVC radiation from the sun in the earth's atmosphere?
- This Wikipedia article discusses ultraviolet light:
Wikipedia contributors, 2006. Ultraviolet, Wikipedia, The Free Encyclopedia. Retrieved October 12, 2006.
- 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. Retrieved October 12, 2006.
- This webpage from Dragonfly TV has a video showing how two kids in Southern California carried out their sunscreen project:
TPT. (2007, May 4). Sunscreen by Aaron and Justin. DragonflyTV, Twin Cities Public Television. Retrieved July 1, 2008.
Materials and Equipment
To do this experiment you will need the following materials and equipment:
- 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
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- Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
- 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.
- Make your measurements on a bright sunny day.
- 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.
- 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.
- Subtract the blank plastic reading from the plastic+sun lotion reading. The result shows how much the sun lotion reduced the UV Index.
- Repeat the measurements for each sun lotion you are testing.
- Once you have gone through all of the lotions, go back and repeat the measurements twice more.
- 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.
- 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?
Ask an Expert
- 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?.
If you like this project, you might enjoy exploring these related careers: