This paper evaluates the effect of excise taxes and bans on smoking in public places on theexposure to tobacco smoke of non-smokers. We use a novel way of quantifying passive smoking:we use data on cotinine concentration- a metabolite of nicotine- measured in a largepopulation of non-smokers over time. Exploiting state and time variation across US states, wereach two important conclusions. First, excise taxes have a significant effect on passive smoking.Second, smoking bans have on average no effects on non smokers. While bans in publictransportation or in schools decrease the exposure of non smokers, bans in recreational publicplaces can in fact perversely increase their exposure by displacing smokers to private placeswhere they contaminate non smokers, and in particular young children. Bans affectsocioeconomic groups differently: we find that smoking bans increase the exposure of poorerindividuals, while it decreases the exposure of richer individuals, leading to widening healthdisparities.