Newswise, April 3, 2017 — In a perfect world, people would
diligently reapply suncreen every couple of hours to protect their delicate
skin from damaging solar radiation. But in reality, few people actually adhere
to reapplication guidelines, and those who do hardly relish the task.
To develop longer-lasting sunscreens, researchers are trying
to answer a basic question: How do sunblock ingredients work?
The researchers presented their work at the 253rd National
Meeting & Exposition of the American Chemical Society (ACS). ACS, the
world’s largest scientific society, is holding the meeting here through
Thursday. It features more than 14,000 presentations on a wide range of science
topics.
“Sunscreens have been around for decades, so you’d think we
know all there is to know about them — but we really don’t,” Vasilios Stavros,
Ph.D., says.
“If we better
understand how the molecules in sunscreen absorb light, then we can manipulate
the molecules to absorb more energy, and we can protect the molecules from
degradation. If the molecule doesn’t break down, there's no need to reapply.”
A typical sunscreen sold at a drug store contains many different ingredients, Stavros explains.
“We wanted to break
these lotions and creams down like a jigsaw puzzle — take one of the
ingredients and understand it from a molecular point of view without
interactions from the other component parts.”
The researchers, who are at the University of Warwick (U.K.),
started by focusing on sunscreen ingredients called chemical filters, which are
molecules that absorb UV light. They have studied about 10 common chemical
filters so far.
When these molecules absorb energy from the sun, Stavros
explains, they enter into an excited electronic state. Other molecules are
likely to break under the sun's glare, sometimes releasing dangerous free
radicals. But instead of breaking, chemical filters can shimmy and shake themselves
back into the more stable ground state, releasing energy as harmless heat. The
problem is that these chemical filters can fail, breaking into pieces or
getting stuck in the excited state.
To figure out how to prevent chemical filter dysfunction,
Stavros’ team used lasers to simulate the sun’s energy and to monitor the flow
of energy through the chemical filters as the molecules traverse from the
ground state to the excited state and back again (or not).
For example, the researchers found that about 10 percent of
the molecules of the sunscreen ingredient oxybenzone get locked in an excited
state when the laser is shone on them.
“When that chemical
filter is in an excited state, its atoms are rotating around certain bonds,”
Stavros says. “If we can manipulate this rotation by adding different chemical
groups, we could help the molecule find its way back to the ground state,” he
says, noting that they plan to work on this project soon.
In addition, the researchers are beginning to study the filters
in a context that is more similar to an actual sunscreen, rather than in
isolation. “We are increasing molecular complexity, building the jigsaw
puzzle,” Stavros says.
He adds that analyzing the data has been a challenge, but one
that the team is tackling head-on. In the end, the data analyses and chemical
manipulations should shed more light on how sunscreens protect against sun
damage so researchers can develop longer-lasting concoctions.
Stavros acknowledges funding from the Engineering and Physical
Sciences Research Council, the Royal Society, The Leverhulme Trust and the
University of Warwick (all in U.K.).
The American Chemical Society is a nonprofit organization
chartered by the U.S. Congress. With nearly 157,000 members, ACS is the world’s
largest scientific society and a global leader in providing access to
chemistry-related research through its multiple databases, peer-reviewed
journals and scientific conferences. ACS does not conduct research, but
publishes and publicizes peer-reviewed scientific studies. Its main offices are
in Washington, D.C., and Columbus, Ohio.
