Secondhand smoke exposure 'affects memory'.
The Northumbria University study is the first to explore the relationship between exposure to other people's smoke and everyday memory problems.
Dr Tom Heffernan and Dr Terence O'Neil, both researchers at the Collaboration for Drug and Alcohol Research Group at Northumbria University, compared a group of current smokers with two groups of non-smokers.
The non-smokers were those who were regularly exposed to secondhand smoke and those who were not.
Those exposed to secondhand smoke either lived with smokers or spent time with smokers, for example in a designated smoking area.
The three groups were tested on time-based memory - remembering to carry out an activity after some time -- and event-based memory, which refers to memory for future intentions and activities.
Researchers found that the non-smokers who had been exposed to secondhand smoke forgot almost 20% more in the memory tests than those non-smokers not exposed.
However, both groups out-performed the current smokers, who forgot 30% more than those who were not exposed to secondhand smoking. Dr Heffernan said: "According to recent reports by the World Health Organisation, exposure to secondhand smoke can have serious consequences on the health of people who have never smoked themselves, but who are exposed to other people's tobacco smoke.
"Our findings suggest that the deficits associated with secondhand smoke exposure extend to everyday cognitive function."