This mix turns pink when sunscreen wears thin | Science News for Students

This mix turns pink when sunscreen wears thin

A teen designs an indicator to signal when it’s time to reapply sunblock
May 23, 2017 — 12:00 pm EST
applying sunscreen

Many people only apply sunscreen when they first go into the sun. A teen has invented a reminder to about when it's time to reapply and stay protected.  


LOS ANGELES, Calif. — Too much sun can lead to burns and blisters, even for those with dark skin or a tan. Beyond the pain, sunburns can increase the risk of skin cancer. 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.

The junior at Star College Girls’ High School in Durban, South Africa presented her new product here at the Intel International Science and Engineering Fair (ISEF). Created by Society for Science & the Public and sponsored by Intel, the yearly fair brings together high school students from around the world to show off their research projects. This year, nearly 1,800 students from more than 75 countries attended, competing for individual prizes worth up to $75,000. (The Society also publishes Science News for Students and this blog.)

“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.

Farah Shaik
Farah Shaik poses with her poster at Intel ISEF
B. Brookshire/SSP

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.”

Some companies sell photochromic chemicals in stickers. The idea is the same as Farah’s. Users can put the sticker on their skin and cover it with sunblock. When the sticker’s colors glow bright, it’s time to put on some more sunscreen.

Farah sees her product as something similar that people would apply before they put on their sunscreen. But they could be more creative than simply applying a sticker. “If it was in a sort of roller bottle, a person could apply a small pattern anywhere on their body,” she says. “When they put sunscreen on they would cover that area as well.” At first, the pattern would be protected from UV light by the sunscreen. But when the color re-appears, it would be time to reapply.

Drawing little patterns that appear later like magic might be a fun way to get kids into sun protection, the teen notes. Photochromic compounds come in many colors, and so the patterns people draw could become works of art, all in the name of sunburn prevention. “It’s basically drawing on yourself,” Farah says. “But it’s also helpful.” 

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blog     Short for web log, these Internet posts can take the form of news reports, topical discussions, opinionated rants, diaries or photo galleries.

cancer     Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.

compound     (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.

engineering     The field of research that uses math and science to solve practical problems.

fluorescent     (v. fluoresce) Adjective for something that is capable of absorbing and reemitting light. That reemitted light is known as fluorescence.

high school     A designation for grades nine through 12 in the U.S. system of compulsory public education. High-school graduates may apply to colleges for further, advanced education.

infrared light     A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.

Intel International Science and Engineering Fair     (Intel ISEF) Initially launched in 1950, this competition is one of three created (and still run) by the Society for Science & the Public. Each year now, approximately 1,800 high school students from more than 75 countries, regions, and territories are awarded the opportunity to showcase their independent research at Intel ISEF and compete for an average of $4 million in prizes. 

pigment     A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.

photochromic  A word used to describe a type of chemical that changes its molecular shape when exposed to light. The change in shape can mean the chemical appears to us to have changed color. 

plastic     Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

radiation     (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

Society for Science and the Public  A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: the Regeneron Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).

solution     A liquid in which one chemical has been dissolved into another.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

ultraviolet     A portion of the light spectrum that is close to violet but invisible to the human eye.


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