The scoop on sunscreen: one student uses charts and graphs to find the best way to block harmful sunrays.

Like most teens, 15-year-old Bryce Melton spends summer days outdoors, whether it's camping with the Boy Scouts or taking a hike. But five years ago, he learned a tough lesson: The sun's rays could be harmful. When Bryce was 10, his grandfather got basal cell cancer (abnormal skin-cell growth resulting from overexposure to the sun). After that, his grandfather always slathered on globs of sun-blocking lotion--SPF 45--before going outdoors.

That got Bryce thinking: "I wondered if he had to use that high of an SPF [Sun Protection Factorl and apply that much." So Bryce designed an experiment to determine how different SPFs stack up against each other, and whether applying a thicker layer of sunscreen makes for a safer sun-day. His well-developed procedure led to some surprising results. It also landed him a finalist position in a national science-project contest called the Discovery Channel Young Scientist Challenge 2003.

RESEARCH RAYS

Bryce read books and searched the Internet to learn more about sunlight which hits Earth as ultraviolet (UV) radiation (invisible energy waves). He found that when yon bask outdoors, these UV rays can wreak havoc on your skin cells. They can even damage your skin's DNA (chemical that carries hereditary information), and lead to cancer.

Good thing your body has a natural sun buster. When sunlight hits your skin, special skin cells churn out loads of melanin (MEH-luh-nin), or a dark-brown pigment. Not only does melanin give your skin a "tan" color, it also absorbs UV radiation. That helps to keep skin cells safe.

Even though melanin is a tough shield, it can't protect you all by itself. Coating your skin with sunscreen can further block the radiation. Sunscreen lotions use chemicals that absorb the UV light. But as Bryce discovered, all sunscreens aren't created equal.

GET READY

To find the perfect sunscreen combination, Bryce experimented with four SPFs--8, 15, 30, and 45--and three sunscreen concentrations (mass per area). The Food and Drug Administration (FDA) recommends a sunscreen thickness of 2 milligrams per square centimeter (mg/[cm.sup.2])--a golf-ball size glob for an adult. Bryce found that most sunbathers are skimpy with the lotion, using a quarter to half of that amount. So he tested concentrations of 1/2, 1, and 2 mg/[cm.sup.2].

Keeping track of these variables (characteristics in an experiment that change or could be changed) could spell chaos. So Bryce used a data table (arrangement of variables in columns and rows). "It was an organization chart, so I would know what numbers I found," says Bryce.

LIGHTS, CAMERA, ACTION

Testing out sunscreens can be a challenge. The FDA studies sunscreens by slathering them onto a person's body. That was a problem. "I didn't want to give anybody sunburn," says Bryce. Instead, he used three sheets of photographic paper, which absorbs UV light--as your skin does.

So the photo paper didn't get sticky, Bryce covered the sheets with a clear page-protector. He applied the four SPFs in sections on each page-protector. Each sheet represented a different sunscreen concentration.

Time to catch some rays! Since weather can be fickle, Bryce mimicked the sun by flashing a black light onto each sunscreen-covered sheet for one second. "Black light produces UV-A [a type of UV light], and since the sun's rays are [at least] 98 percent UV-A, it was the closest thing I could get to the sun," explains Bryce.

After the papers received a "tan," Bryce developed them in a darkroom. Then, a professional printer measured the "darkness" of several spots on the photo papers. A "darkness rating" of "zero" meant no light had pierced the sunscreen. A rating of "one" meant that all of the UV light got through.

DECIPHERING THE DATA

Alone, these numbers were useless. So Bryce organized them onto a data table similar to the one below. "I grouped the results by their concentrations, so I could compare the SPFs against each other," says Bryce.

He used the data table to make a graph (similar to the one below) of his results. Since the sunscreen concentration was an independent variable (factor that is changed on purpose), Bryce plotted these numbers on the x-axis (horizontal line on a graph). He plotted the darkness rating--the dependent variable (factor that responds to the change in the independent variable)--on the y-axis (vertical line on a graph).

By analyzing his graph, Bryce was able to crack the sunscreen secret: He found that it doesn't take any higher than SPF 30 to keep skin safe. Bryce's data also showed that 1 mg/[cm.sup.2]--about one tablespoon for an entire adult--gives enough protection. But he warns that the FDA still recommends using 2 mg/[cm.sup.2] of sunscreen. So if you're heading outdoors, grab the sunscreen. Your skin cells will thank you!

Data Table
COMPARING SUNSCREENS

Low = 0.5mg/[cm.sup.2]
Medium = 1.0mg/[cm.sup.2]
High = 2.0mg/[cm.sup.2]

LAYER    TRIAL 1    TRIAL 2    TRIAL 3    AVERAGE

Thin     Darkness   Darkness   Darkness   Darkness
SPF 8    0.87       0.86       0.82       0.85
SPF 30   0.79       0.82       0.84       0.82

Medium
SPF 8    0.67       0.69       0.65       0.67
SPF 30   0.58       0.62       0.62       0.61

Thick
SPF 8    0.71       0.72       0.72       0.72
SPF 30   0.65       0.61       0.56       0.61

Can you think of another way to organize this chart so
that you could compare the sunscreen concentrations?

[ILLUSTRATION OMITTED]

WEB EXTRA

Learn more about sunscreens at this EPA Web site: www.epa.gov/sunwise/doc/sunscreen.pdf

ARTICLE RESOURCES

* Grolier search terms: skin cancer, ultraviolet

* The U.S. Environmental Protection Agency's Sunwise Program offers sun-safety tips. See: www.epa.gov/sunwise