Researchers led by Dr Arthur Brody of the University of California in Los Angeles found secondhand smoke strongly activates nicotine receptors in the brain, leading to cravings.
The researchers said the findings may explain why smokers regularly exposed to secondhand smoke have trouble beginning and maintaining an attempt to quit.
In the study, 24 young adults sat in a car and were either exposed to secondhand smoke, or not exposed, for one hour.
Eleven were moderately dependent cigarette smokers and 13 were non-smokers.
Before and after sitting in the car, participants' brains were scanned using PET to look at whether nicotinic acetylcholine receptors had been activated.
Researchers found both smokers and non-smokers exposed to secondhand smoke had a 19% greater activation of nicotine receptors.
Smokers reported an average increase in craving of 23% following exposure.
