Smokers who inhale their own secondhand smoke add significantly to the health risks linked to cigarette smoking, say researchers.
Until now it has been believed that such risks would be negligible in comparison to those incurred due to actual smoking.
Maria Teresa Piccardo worked with a team of researchers from the National cancer Research Institute, Genoa, Italy, to study the exposure of newsagents in the city to harmful cigarette smoke.
The experts found for someone who smokes 14 cigarettes a day, their own second hand smoke resulted in exposure the equivalent of smoking an extra 2.6 cigarettes.
Piccardo said: "Newsagents were chosen because they work alone in small newsstands, meaning that any tobacco smoke in the air they breathe is strictly correlated to the number of cigarettes smoked by that newsagent. We studied the contribution environmental tobacco smoke made to carcinogen exposure in 15 active smokers.
"Both active and passive smoking contributions should always be considered in studies about health of active smokers."
The study has been published in BioMed Central's open access journal Environmental Health.