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Determine the Screening Ability and Effectiveness of Suntan Lotions

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Author: Janice VanCleave

Exposure of skin to rays from the sun is unavoidable, but many people purposely bathe their bodies in these rays to achieve a "perfect tan." Some people want to prevent overexposure and pain of sunburn. Many manufacturers provide suntan products that are advertised to protect the skin from the sun and promote tanning.

In this project, you will determine the screening ability of suntan lotions and determine whether sunblock lotions are more effective than tanning lotions. You will also examine the relationship between cost and effectiveness of sunscreening products.

Getting Started

Purpose: To test the effectiveness of suntan lotions.

Materials

  • masking tape
  • clear plastic report folder
  • marking pen
  • 4 brands of sunblock lotion with the same SPF
  • Sunprint photographic paper (Purchase this paper at a nature or toy store.)
  • tap water

Procedure

  1. Use masking tape to divide the top sheet of the report folder into four equal parts. Position the pieces of tape so that one goes down and one goes across the center of the folder.
  2. With the marking pen, number each of the four sections.
  3. Assign a number to each brand of lotion and record it in a data table.
  4. Use your fingers to coat each section of the plastic with the corresponding brand of lotion. Wash your hands before applying each brand and make sure you apply equal thicknesses of lotion to each section.
  5. In a semidarkened room, remove a sheet of developing paper from its protective container. Close the container tightly to protect the remaining sheets from light exposure.
  6. Raise the lotion-coated plastic and place the sheet of developing paper, glossy side up, inside the folder.
  7. Close the folder and set it, lotion side up, outside in the sun (see A in Figure 25.1). Best results occur at midday when the sun's rays are most direct
  8. After five minutes, return the folder to the darkened room.
  9. Follow the instructions on package to fix the photographic paper.
  10. Allow the paper to dry.
  11. Observe the degree of coloration on each section of the paper (see B in figure 25.1). Record your results in a data table such as the one shown here.
  12. Repeat the procedure twice.

Effectiveness of Sunscreens

Effectiveness of Sunscreens

Results

The Sunprint paper remains unchanged under the strips of tape. Under the lotions, the paper has degrees of darkness.

Why?

Sunprint photographic paper is coated with a light-sensitive compound. Exposure to light, like the sun, chemically changes the compound producing a dark color. The amount of change depends on the amount of light that falls on the paper. Thus, the areas shielded from light by the tape remain white. The degree of darkness in the area shielded by the lotions in this experiment indicates the effectiveness of each lotion in blocking out the sun's rays. The water removes the light-sensitive compound on the paper; thus, the image on the paper is fixed (made permanent) so that light no longer turns it dark and you have a permanent record of your results.

Try New Approaches

  1. Do suntan lotions give as much protection as sunblock lotions? Repeat the experiment using samples of suntan and sunblock lotions. Science Fair Hint: Use the exposed Sunprint paper from the different experiments as part of a project display. Label each to indicate the lotion used. Take photographs during the experiment to represent the procedure.
  2. Is there a difference in the protection of differently rated sunblock lotions? Repeat the original experiment using sunblock lotions with low to high number ratings.
  3. Does the price of the product affect how it works? Repeat the original experiment using sunblocks with the same rating but different prices. Do more expensive lotions offer more protection? Divide the product prices into three groups and let each group represent a price range. Science Fair Hint: Use a bar graph to represent your results (see the sample in Figure 25.2).
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