Why do we wear sunscreen?
Goal: Learn the importance of wearing sunscreen to protect you from the harmful effects of ultraviolet radiation.
Experiment with the ability of some materials to block UV radiation.
Appropriate for all ages. You'll need a bright sunny day to run this experiment.
Necessary Materials: Three sheets (or one sheet cut into three pieces) of the same darker-colored construction paper and lip balm with SPF factor 15 or higher.
Everyone is exposed to UV light from the sun every time we go outside. The more time you spend in the sun, the faster it ages your skin.
NGSS Recommendations:
Kindergarten - Weather and Climate, Natural Hazards, K-ESS3.B
1st grade - Light and Sound, 1-PS4-3
2nd grade - Structure and Properties of Matter, 2-PS1.A
K-2 Engineering Design - Why do we wear sunscreen at the beach?
Background:
Light that comes from the Sun is not exactly the same as the light from a light bulb. Sunlight has a few extra types of light mixed in - mostly infrared (IR) and ultraviolet (UV) light.
Infrared light carries heat, which is why you feel warm standing in the Sun (but you don’t feel warmer standing under a fluorescent or LED light bulb, which don’t produce much heat).
Ultraviolet light from the Sun (and other places, like tanning booths and nail salons) can cause damage to some materials. When the Sun hurts your skin, we call this a sunburn. Sunburns can be itchy and painful and can cause long-term damage if you get them a lot. Sunscreen can block this damage for a while and protect your skin, so it’s important to wear sunscreen if you’ll be outside in the Sun. For more information, see our article on types of UV light.
Procedure:
Pick three sheets of brightly colored construction paper of the same color (or cut one piece into three pieces).
Draw on all three pieces of paper with SPF lip balm. Don’t cover the whole paper, just some parts of it.
Place one sheet of the paper outside in direct sunlight (consider weighting it down so it doesn't blow away). Place the second sheet inside in direct light from closed window. Place the third sheet of paper inside away from direct sunlight (regular indoor lighting is fine).
Wait at least half an hour. The longer you wait, the more pronounced the effect will be!
Observation:
The color of the construction paper has faded due to exposure to UV light from the Sun. However, the parts you covered with lip balm (and the optional spray-on sunscreen) should be close to the original color of the paper.
The paper outside in direct sunlight will experience the most fading. The paper inside in direct sunlight experiences less fading, and the paper not in sunlight faded the least.
Have the students try ranking the three pieces of paper by which faded the most/least.
Science:
What happened?
UV light carries more energy than visible light. When absorbed by the paper, the light has enough energy to break down chemical bonds, like those used in the dye for the paper (which is why cheap construction paper works best for this experiment, unlike higher-quality papers with UV-resistant dyes).
Sunscreen can work in two ways - as a physical block or a chemical block (and many types are a combination of the two!). The white goopy types of sunscreens are physical blockers; they contain small mineral particles in a suspension that stay on the surface of your skin and reflect the UV light away, like tiny mirrors. Chemical blocking sunscreens contain chemicals that absorb the UV radiation before it gets to your skin underneath.
Covering parts of the construction paper with sunscreen (like lip balm with SPF) protects the chemical dyes underneath from the harmful effects of UV radiation, just like sunscreen protects your skin - but only for a while! It must be reapplied regularly to maintain its effects.
Sunlight carries three types of UV light (types A, B, and C) but only the lower-energy types A and B make it all the way to the surface of the Earth (see our article on types of UV light to learn why!). UV-A light has less energy than UV-B light. UV-A light will eventually cause wrinkles, age spots, and age lines on our skin. Electromagnetic radiation (light) with enough energy to break down chemical bonds is known as ionizing radiation and has the potential to damage DNA. Long-term exposure to ionizing radiation can lead to cancer. UV-B light includes ionizing radiation, which is why we wear sunscreen when we go outside - to minimize the harmful effects of sunlight.
But wait! People and animals have always been exposed to sunlight. Why is it only people who need to put on sunscreen? And isn’t sunscreen a new invention?
Well, kinda. Most animals have hair or fur to block many of the harmful effects of the sun, while people mostly don’t (except for on the top of our heads - probably one of the reasons that didn’t go away with the rest of our body hair when we evolved!). Animals without much fur or hair (like pigs!) do, in fact, get sunburned.
While the sunscreen you buy from the drug store and spray on is a relatively new invention, the idea of blocking sunlight from hitting your skin is not. Clothing (hats, scarves, loose light-colored robes that don’t easily absorb light) is another easy way to block the sun from your skin, and ancient people had other methods as well - umbrellas, getting into the shade, and even concocting early versions of today’s sunscreens from locally-available materials. Learn more at History.com!