Introduction:
Accurate estimation of exposure to Secondhand Smoke (SHS) is important in both research and clinical practice. We aimed to develop, an easy to implement, biomarker validated scale to provide an estimation of adult exposure to SHS for use within primary health care or epidemiological research.

Methods:
A pool of 26 baseline questions evaluating exposure to SHS was administered to 178 non-smoking adults (mean age 68.1 years), recruited from both urban and rural primary health care practices in Crete, Greece in November 2011, while concurrent hair samples were collected and nicotine concentrations were measured. To generate scores for each question item, we fitted a backward linear regression using the main predictors of SHS exposure selected from the initial pool of questions, weighted against each individuals biomarker evaluated exposure.

Results:
Among the pool of participants and weighted according to hair nicotine levels, in descending order, the most important sources of SHS exposure were the home (5 points, β=0.37), the family car (3 points, β=0.20), public places (2 points, β=0.15) and the workplace (1 point, β=0.013), the relative weighting of which led to the development of an 11-point scale to assess exposure to SHS. For every unit increase in the score, there was an associated increase in mean hair nicotine concentrations by 1.35 ng/mg (95%CI: 1.25-1.45, p<0.0001)

Conclusions:
The SHS exposure score (SHSES) may be a useful tool in an estimating the level of the exposure to SHS among elderly adults and investigating the relationship between SHS exposure and potential health outcomes.