Whether you're a smoker or a non-smoker, chances are you have strong opinions on passive smoking, including whether or not it represents a genuine risk to health.
And now a major World Health Organisation study involving no less than 192 countries has come to a stark conclusion. Every year, it claims, passive smoking causes more than 600,000 premature deaths, with children being most at risk and more women likely to be affected by men.
It's the first study to assess the impact of passive smoking - that is, breathing in someone else's cigarette smoke - on a global level. And its findings, which have just been published in the medical journal The Lancet, make highly uncomfortable reading.
Based on data from 2004, the survey suggests during that year smoking killed almost six million people worldwide - that's actively and passively. But passive smoking was linked to around 603,000 of those, including 379,000 deaths from heart disease, 21,400 from lung cancer, 165,000 from respiratory infections and 36,900 from asthma.
The WHO researchers claim up to 40 of women and 33 more likely to be affected than men. It's particularly dangerous for children, they add, who have a higher risk of pneumonia, asthma and sudden infant death syndrome (cot death) than adults.
"Breathing in other people's tobacco smoke has deadly consequences," says Betty McBride of the British Heart Foundation.
"These figures should make smokers stop and think about the impact they're having on other people's health, particularly children's."
Strong words, but do you agree?