It's clear from this study that by smoking, you not only put your own life in jeopardy, but risk the health of your loved ones too

Jean King

The results confirm how difficult it is to avoid other people's tobacco smoke, the team from ICRF's Health Behaviour Unit concluded.

Jean King, Director of Education for the Cancer Research Campaign said: "It's clear from this study that by smoking, you not only put your own life in jeopardy, but risk the health of your loved ones too."

Researchers looked at the affects of living with an average smoker (one who smoked 15 cigarettes a day) which put them at four times the risk of breathing in smoke.

'Worrying'

Professor Martin Jarvis OBE and his team also found that a non-smoker living with a heavy smoker (30 cigarettes a day) breathed in six times as much smoke.

Professor Jarvis said: "There seems little doubt that the home is now the major source of exposure to second hand smoke for most non-smokers.

"These findings are very worrying as they mean that a large group of people are being exposed to a significantly increased risk of lung cancer and other smoking related diseases, but are probably powerless to do anything about it."

The study also found that a person's sex, age and social environment had an affect on their exposure to second hand smoke.

The researchers found that non-smoking men experienced a third more exposure to cigarette smoke than women.

Age factor

Non-smokers in deprived areas had 50% more exposure to passive smoke than people living in affluent areas.

Professor Jarvis also found that non-smokers living in the north had a greater exposure to cigarette smoke than those in the south.

And age had an affect too - young people were at most risk of tobacco smoke exposure.

The charity urges smokers to give up

The time of year had an affect. There was more effect from smoke in the autumn and winter than in spring and summer.

The team used data from the Health Survey for England and looked at the level of cotinine (a nicotine breakdown product found in the blood of those exposed to tobacco smoke) in over 9,000 non-smokers and their partners.

It revealed that only 10% of all non-smokers had no measurable cotinine.

The study found that levels of cotinine rose from 0.31ng/ml (nanogrammes per millilitre of blood plasma) in those not exposed to smoke in the home, to 1.25ng/ml in those whose partners smoked between 15 and 19 cigarettes per day.

And it rose to 1.99ng/ml in those whose partners smoked 30 or more per day.

The Imperial Cancer Research Fund urges people to quit smoking and avoid the risks associated with it.

Jean King said recent research shows that even if you quit at the age of 60 you can reduce your risk of lung cancer.

"So our message for smokers is that for your own sake, and for your nearest and dearest, quit now," she said.

The researchers admit that they had no way of measuring other potential sources of exposure outside the home.

Their survey took place in 1994 and 1996.