New Delhi: Church candles and incense can be dangerous to the lungs, according to a study by Dutch scientists.

Church air appears considerably higher in cancer causing "polycyclic" hydrocarbons than air beside busy roads and it has particulate matter levels of up to 20 times the European limits, says the study.

With all those church candles lighting up for Christmas, December could be an especially dangerous month for the lungs, according to a communication by 'The Netherlands Research Team', to be published in December's 'European Respiratory Journal'.

Theo de Kok and his team from the University of Maastricht (The Netherlands), reached the conclusion after an unusual experiment wherein they analysed particulate matter concentration found in the air of a small chapel and a large basilica in Maastricht following lengthy use of candles or a simulated service in which incense was burnt.

Fine particulate matter contains different types of toxic chemicals, including soot, metals and various carcinogenic molecules. The particles can penetrate very deep into the lungs and trigger various lung and heart conditions.

So the Maastricht team set out to examine air quality in churches, which are traditionally poorly ventilated, with candles burning all day long and frequent use of incense. Both could, in principle, be expected to have some harmful effects.

The scientists found that after the usual nine hours of candle-burning, the church air had particulate levels of 600 to 1000 micrograms per cubic metre, or 12 to 20 times the European allowed average concentration over 24 hours.

The team also found very high concentrations of polycyclic aromatic hydrocarbons, well-known to be carcinogenic, as well as various types of free radicals, including some previously undocumented ones.

Free radicals are highly reactive molecules that damage lung tissue and can trigger asthma and chronic bronchitis, the study said.