Experts say rooms should be ventilated when burning candles
Candle-lit dinners may be romantic, but researchers are warning they could be harmful to health.
South Carolina State University experts analysed the fumes released by burning candles in lab tests.
They found paraffin wax candles gave off harmful fumes linked to lung cancer and asthma - but admitted it would take many years' use to risk health.
UK experts said smoking, obesity and alcohol were much more important in terms of cancer development.
And even the researchers admitted occasional candle use was not something people should worry about too much.
Researcher Amid Hamidi said people who frequently used candles, for instance to help them relax in the bath or provide the right ambience for dinner, were most at risk.
He told the American Chemical Society in Washington: "An occasional paraffin candle and its emissions will not likely affect you.
"But lighting many paraffin candles every day for years or lighting them frequently in an un-ventilated bathroom around a tub, for example, may cause problems."
To investigate candle emissions, the researchers burned a range of candles in the laboratory and collected the mixture of substances they gave off.
Paraffin-based candles produced "clear sharp peaks" for many chemicals, mainly because burning candles does not produce high enough temperatures to combust hazardous molecules such as toluene and benzene.
The scientists suggested switching to candles made from beeswax or soy, which did not release significant levels of the chemicals.
But Dr Joanna Owens, from Cancer Research UK, said: "There is no direct evidence that everyday use of candles can affect our risk of developing cancer.
"In terms of cancer, a far more significant type of indoor air pollution is second-hand cigarette smoke.
"When talking about cancer risk, it's important to focus on things we have hard evidence for.
"Lifestyle factors such as smoking, alcohol, obesity, unhealthy diets, inactivity and heavy sun exposure account for a much larger proportion of cancers."
Dr Noemi Eiser, medical director at the British Lung Foundation, added: "We would like to reassure people that occasional use of paraffin candles should not pose any risk to their lung health."
But she added people should still take "sensible precautions" such as ventilating rooms when burning candles.