Here's a warning to sunbathers everywhere.
Scientists have found that the skin damage
caused by UV rays does not stop once you get
out of the sun.
Chemical changes
Researchers say that much of the potentially
cancer-causing damage wrought by ultraviolet
radiation from sunlight or tanning beds occurs
up to three to four hours after exposure,
thanks to chemical changes involving the
pigment melanin.
But there is some good news. The researchers
said it may be possible to develop sunscreen
that protects against this type of damage.
Melanoma, closely linked to UV exposure,
accounts for most skin cancer deaths.
The role of melanin, responsible for our skin,
eye and hair colour, in promoting DNA
damage was a surprise because melanin was
previously known to play a protective role by
absorbing much of the UV energy before it
penetrates the skin.
"But the unusual chemical properties of
melanin that make it a good UV absorber also
make it susceptible to other chemical
reactions that just happen to have the same
end result as the UV," said Douglas Brash, a
therapeutic radiology and dermatology
professor at the Yale School of Medicine
whose study appears in the journal Science.
The researchers revealed this aspect of
melanin in experiments involving human cells
in a lab dish as well as lab mice and mouse
cells in a dish.
cancer-causing damage wrought by ultraviolet
radiation from sunlight or tanning beds occurs
up to three to four hours after exposure,
thanks to chemical changes involving the
pigment melanin.
But there is some good news. The researchers
said it may be possible to develop sunscreen
that protects against this type of damage.
Melanoma, closely linked to UV exposure,
accounts for most skin cancer deaths.
The role of melanin, responsible for our skin,
eye and hair colour, in promoting DNA
damage was a surprise because melanin was
previously known to play a protective role by
absorbing much of the UV energy before it
penetrates the skin.
"But the unusual chemical properties of
melanin that make it a good UV absorber also
make it susceptible to other chemical
reactions that just happen to have the same
end result as the UV," said Douglas Brash, a
therapeutic radiology and dermatology
professor at the Yale School of Medicine
whose study appears in the journal Science.
The researchers revealed this aspect of
melanin in experiments involving human cells
in a lab dish as well as lab mice and mouse
cells in a dish.
Damage after UV exposure
UV exposure can cause DNA damage that mayspur carcinogenic mutations in melanin-
producing cells called melanocytes.
The researchers exposed mouse and human
melanocytes to radiation from a UV lamp. The
cells experienced DNA damage immediately
but the damage also continued for hours. In
fact, half of the damage occurred in the hours
after exposure.
After a type of chemical reaction called
chemiexcitation, also witnessed in
bioluminescent creatures including fire flies,
energy gets transferred to DNA to potentially
cause mutations .
"People should be aware of the chemistry
initiated in the skin after the UV exposure so
that they can take proper care of themselves
whenever going out in the sun or to the
beach," said Yale School of Medicine
researcher Sanjay Premi.
"We'd like to find new ingredients for
sunscreens that will block these reactions,"
Brash added. "But in the meantime, I tell
people to enjoy the sun but just don't lie on
the beach between 10 a.m. and 2 p.m., and
wear a hat. Sunscreens are useful, too, so
long as they block both UVB and UVA," two
kinds of ultraviolet rays.
- Reuters
