This Mix Turns Pink When Sunscreen Wears Thin By Bethany Brookshire

May 23, 2017

LOS ANGELES, Calif. — Too much sun can lead to burns and blisters, even for those with dark skin or a tan. Sunscreen can help, but it wears off—and people forget to reapply. With the power of chemistry, though, Farah Shaik, 16, has created a reapplication reminder. When sunscreen gets thin, this reminder turns pink to remind a person they need to slather on more sunblock.

“In South Africa we have a lot of sunlight. Most of the year is spent with the sunshine, so my friends and I spend a lot of time outside and we need to protect ourselves,” Farah says. “Sunscreen is the most effective way to do that.” Sunscreen is meant to protect skin from ultraviolet—or UV—light from the sun. We can’t see this light with our eyes. But the light can burn the skin if it’s exposed for too long. Sunscreen provides only a temporary shield, and those who forget to reapply can easily become burned.

After one too many burns, Farah decided to find something that would let her know when she needed to put on more sunscreen. She was inspired by an old arts and crafts project. Her father had bought her some photochromic beads —plastic beads that are white indoors but turn vivid colors in the sun. A photochromic chemical changes shape when it absorbs certain types of light. For some chemicals, that shape change alters an object’s color. A powder or bead that is white indoors can turn vivid blue, pink or yellow in the sun.

“I thought about what the beads contained, and I realized they contained a photochromic pigment,” Farah says. She thought that the pigment, or something like it, might make a good indicator for when it was time to reapply sunscreen. “It made sense because [the beads] changed color in response to UV light,” she notes.

Farah bought a small amount of a photochromic chemical called spiropyran. It turns bright pink in UV light. But she needed a way to apply the powder to the skin. She consulted with dermatologists—doctors who study the skin—as she developed a mix of chemicals that would let her easily apply the spiropyran. The doctors helped to ensure the chemicals she was using would be safe. In her kitchen, the teen mixed the powder with water, glycerin (found in bath products such as soap or lotion) and a few other chemicals to make a foam.

After making mixtures of 2.5 percent, 5 percent and 10 percent spiropyran, the teen began her tests. First, she put the solutions in full sunlight to see how long it took for their color to change. Farah also tested the chemical mixes under different types of light: UV light from a lamp, infrared light (another type of light we can’t see) and indoor fluorescent lights.

Only the UV light and sunlight made the mixtures turn pink, and the 10 percent solution was the brightest, the teen found. Coating the mixture with sunblock, though, effectively stopped the color change. When the sunblock wore off, the chemical went from zero to pink in about 30 seconds. “It’s a really quick change, which is good,” Farah says. “When the sunscreen wears off, you want to know immediately. You don’t want there to be any delay.”
What technique does the author use to help readers better understand the science behind Farah’s invention?
A.
She uses metaphors and similes.

B.
She provides complex data and numbers.

C.
She defines difficult words and concepts.

D.
She cites direct quotes from Farah.