In response to the accumulating evidence about the considerable impact of exposure to second-hand smoke, researchers from the University of California have conducted a review of the evidence of its biological effects compared with the effects of active smoking. They concentrated on low doses of exposure and placed greater emphasis on research published since 1995. Through analyzing 29 studies, the researchers found that the dose of smoke received by an active smoker is at least 100 times the dose received by a passive smoker. However, passive smoking has much larger cardiovascular effects than would be expected by comparing the doses delivered to active and passive smokers. In many cases, the effects of even brief passive smoking are often nearly as large as long-term active smoking. They report that the impact of second-hand smoke on the cardiovascular system is similar to, but larger than, the effects of outdoor air pollution. The effects of second-hand smoke are substantial and rapid, they write, which explains the relatively large risks that have been reported in population-based studies and earlier reviews of the evidence.

In conclusion, the authors state that there is consistent evidence that passive smoking has a much larger effect than would be expected from the dose of toxins received. The effects of even brief exposures are 80- 90 per cent as large as from active smoking, and the means by which they occur are numerous and impact on each other. They support the implementation of smoke-free policies, particularly in the workplace, in order to reduce passive smoking and encouraging current smokers to quit.
Barnoya, J and Glantz, S.A. Cardiovascular Effects of Secondhand Smoke. Nearly as Large as Smoking. Circulation, Vol. 111, May 2005, pp. 2684-2698