UVB more damaging to skin than UVA
US scientists have discovered that one type of ultraviolet (UV) light is more likely to cause skin cancer than the other because the skin cells are less able to repair the damage it causes to DNA.
Researchers at the City of Hope National Medical Centre in California found that the human body is less able to repair the DNA damage caused by UVB light than that caused by UVA light, a discovery that helps to explain why UVA is regarded as somewhat less damaging than UVB.
The team exposed one set of mouse cells to UVA light, a second set of cells to UVB light, and a third to simulated sunlight.
They found that all of the cells sustained DNA damage, and that those exposed to UVB light were less able to repair the damage.
This appeared to be because of the nature of the damage. UVA caused the 'purine' bases in DNA to become oxidised and break down, whereas UVB caused 'pyrimidine' bases to stick together - a much harder type of damage for the cell to repair.
However, the team emphasised that both forms of damage can lead to skin cancer.
Dr Gerald Weissmann, editor-in-chief of the Faseb journal in which the study is published, commented: "We know that sunlight causes skin cancer and that breakdown of the ozone layer exposes us to ever more ultraviolet radiation.
"This work tells us that both forms of UVA and UVB in sunlight cause damage to DNA. It forms a missing link in the chain of events from sun exposure to tumour formation."
Dr Weissmann said that the findings could help scientists to develop more effective sunscreens and after-sun products, adding: "It promises new ways to prevent - and perhaps to treat - the epidemic of skin cancer brought on by modern life."