Sunscreen Experiment

3.5 based on 8 ratings
Updated on Oct 12, 2012

You’ve been hearing about it since your child’s infancy: whenever you take your kid out into the sun, you need to watch out for those dangerous rays! Lots of kids fight the stuff. But now that your child is in third grade, you can do some exciting science work together, to discover some of the “whys” behind all those lotion slathering sessions. Here’s how:

What You Need:

  • Sheet of 8-1/2”x11” clear plastic acetate (available at many office supply stores).
  • Scissors
  • Ruler
  • Black permanent marker
  • Three “protection levels” of sunscreen: we suggest SPF 4-8; SPF 15; and SPF 45.
  • Photoreactive paper (available at science supply stores and some toy stores).
  • Plain cookie sheet
  • 9x13” dish of water (we use a pyrex cooking dish)

What You Do:

  1. Explain to your child that you will be taking a look at what’s really happening when you smooth sunscreen onto your skin. You may want to laugh a little together first—in plenty of families, “sunscreen explosions” happen clockwork: mom spreads it on and kid yowls! But once that’s done, what’s going on?
  2. Now take out the clear plastic sheet. (Note: you will use the kind of plastic that many businesses use for making presentations; it’s available by the pack in office supply stores). Use your ruler to mark one vertical and one horizontal dividing line, and then cut four “panes.” Mark one pane “O SPF”—this will be your “control.” Mark the other three panes with the SPF of each of your three sunscreen “levels”—one pane for each level.
  3. Measure about 1/4 teaspoon of each kind of lotion, and use your finger to smooth it carefully over its appropriate “pane” on your plastic. (Remember: one pane will have no sunscreen at all).
  4. For the next stage—the photoreactive paper—be prepared to work quickly, and read the specific package instructions carefully. For a typical photoreactive paper pack, quickly remove four pieces from their protective envelope, place them on the cookie sheet, and then cover them immediately with the four sheets of plastic that you have just prepared.
  5. Place the cookie sheet in full sun, with no parts shaded, and leave it there for 1-4 minutes, or until the SPF 0 page look nearly white.
  6. Bring the sheets inside, carefully take the plastic sheets off, and use your marker to write its correct SPF. Then, following package directions, rinse the papers in  the water tray (some papers also come with a “fixing” solution, but we prefer the simplicity of those that just use water).
  7. Which sunscreen worked the best? Parents, you’ll probably be able to guess…but let’s see what your child concludes. With luck, your experiment may have some serious lifetime benefits!
Julie Williams, M.A. Education, taught middle and high school History and English for seventeen years. Since then, she has volunteered in elementary classrooms while raising her two sons and earning a master's in school administration. She has also been a leader in her local PTA.

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