New York: Rates of one form of skin cancer may be elevated in areas with naturally high levels of the radioactive gas radon, a UK study suggests.
But researchers caution the findings do not prove that radon raises people`s risk of the disease, known as squamous cell carcinoma -- a highly curable type of skin cancer.
Their study looked only at wider geographical patterns, showing a correlation between an area`s radon levels and rates of the skin cancer.
Radon -- a gas produced from the decay of naturally occurring uranium in soil and water -- is already considered a risk factor for lung cancer.
The US Environmental Protection Agency (EPA) estimates that radon contributes to about 21,000 lung cancer deaths each year -- although smoking is also involved in the majority of those cases.
For the new study, reported in the journal Epidemiology, UK researchers looked at skin cancer rates across 287 postal codes in southwest England.
They found that the rates of squamous cell carcinoma varied by postal code. In some areas, the yearly rate was about 35 cases or fewer per 100,000 people; in others, it was as high as 182 cases per 100,000.
There was an association between an area`s average household radon level and its rate of squamous cell skin cancer. In postal codes where the radon level topped 230 Becquerel per cubic meter (Bq/m3), the rate of the cancer was 76 percent higher versus areas with the lowest average radon levels.
In the UK, radon levels above 200 Bq/m3 are considered "action" levels -- that is, people are advised to take steps to cut their home`s radon concentration.
That can mean measures like sealing off cracks in basements and floors, and installing ventilation systems.
In the US, the EPA suggests taking those steps if home radon levels are around 150 Bq/m3. (The agency uses a different unit, giving the threshold as 4 picoCurie per liter, or pCi/L.)
The current study did not measure people`s actual exposure to radon, which would vary by household even within a postal code with a high radon level, according to lead researcher Benedict W. Wheeler of the University of Exeter.
"This type of study is at the population/area level, so we only know that areas with high average household radon tend to also have high population rates of squamous cell carcinoma," Wheeler told a news agency in an email.
"It is possible that this relationship does not exist at the individual level," he added.
The researchers also had no information on people`s individual behavior -- including how much time they spent in the sun, which is a key factor in skin cancer risk.
But if people in high-radon areas tended to spend more time in the sun, you`d expect to see higher rates of basal cell carcinoma as well, Wheeler noted.
Basal cell carcinoma is the most common form of skin cancer. Unlike melanoma -- the least common but deadliest skin cancer -- both basal cell and squamous cell cancers are rarely fatal.
In this study, however, radon levels were unrelated to rates of basal cell cancer or melanoma.
Wheeler said it is plausible that radon could specifically raise the risk of squamous cell cancers. Those tumors form in the more superficial layers of skin, while basal cell cancers arise in deeper layers. And radioactive particles from radon would not be expected to penetrate that deeply into the skin; the particles, Wheeler said, can be stopped by a sheet of paper.
A radon expert not involved in the study agreed.
"Radon decay products deposit on skin in a similar manner to how they plate out on surfaces in a home," said R. William Field, a professor at the University of Iowa College of Public Health who studies the health effects of radon.
Some researchers have suggested that radon exposure could be behind two percent of non-melanoma skin cancers, he said.
Now, Field said, more rigorous studies are needed to see whether people`s individual exposure to radon is related to their skin cancer risk. He said that will require "case-control" studies, where people with squamous cell cancer are compared with people without the disease.
Wheeler agreed that further studies are necessary.
And he said that avoiding excessive sun exposure remains your best bet for cutting your skin cancer risk.
"The number-one risk factor for skin cancer in most cases is still UV from the sun," he noted, "and people should be aware of `safe sun` guidance given by public health authorities."
When it comes to radon, the EPA suggests that all homes be tested, due to the lung cancer risk. Some state programs offer free or low-cost test kits; the agency has information on state radon contacts at http://www.epa.gov/radon/radontest.html.
The EPA estimates that for every 1,000 non-smokers exposed to 4 pCi/L of radon over a lifetime, seven could develop lung cancer. That`s on par with the risk of dying in a car crash.