America
Ultraviolet radiation may damage skin hours after sun exposure
Washington, Feb 20
Would we need a sunscreen
for the night? Yes, we might because much of the damage that ultraviolet
radiation (UV) does to skin occurs hours after sun exposure, say
researchers, including one of Indian-origin.
Exposure to UV light
from the sun or from tanning beds can inflict certain type of DNA
damage that causes skin cancer even in the dark, the findings showed.
The
study could lead to new preventive tools, such as an "evening-after"
sunscreen, the researchers from Yale Yale School of Medicine added.
In
the current study associate research scientist Sanjay Premi, professor
Douglas Brash and co-authors first exposed mouse and human melanocyte
cells to radiation from a UV lamp.
Melanocytes cells make the melanin that gives skin its colour even in the dark,
The
radiation caused a type of DNA damage known as a cyclobutane dimer
(CPD), in which two DNA "letters" attach and bend the DNA, preventing
the information it contains from being read correctly.
To the
researchers' surprise, the melanocytes not only generated CPDs
immediately but continued to do so hours after UV exposure ended. Cells
without melanin generated CPDs only during the UV exposure.
This finding showed that melanin had both carcinogenic and protective effects.
"If
you look inside adult skin, melanin does protect against CPDs. It does
act as a shield," said Brash. "But it is doing both good and bad
things," he added.
The researchers next tested the extent of
damage that occurred after sun exposure by preventing normal DNA repair
in mouse samples.
They found that half of the CPDs in melanocytes were "dark CPDs" -- CPDs created in the dark.
The study was published online in the journal Science.