Non-smokers who live with or spend time with smokers are damaging their memory, according to new research from Northumbria University.
The findings, published in the latest online edition of the journal Addiction is the first study 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 - those who were regularly exposed to second-hand smoke and those who were not.
Those exposed to second-hand smoke either lived with smokers or spent time with smokers, for example in a designated "smoking area," and reported being exposed to second-hand smoke for an average of 25 hours a week for an average of four and a half years.
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 second-hand 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 second-hand smoking.
Dr Heffernan said: "According to recent reports by the World Health Organisation, exposure to second-hand 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 second-hand smoke exposure extend to everyday cognitive function. We hope our work will stimulate further research in the field in order to gain a better understanding of the links between exposure to second-hand smoke, health problems and everyday cognitive function."