This paper evaluates the effect of excise taxes and bans on smoking in public places on the exposure 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 large population of non-smokers over time. Exploiting state and time variation across US states, we show that excise taxes have a significant effect on passive smoking but smoking bans have contrasting effects on non-smokers. While bans in public transportation or in schools decrease the exposure of non smokers, bans in recreational public places perversely increase their exposure by displacing smokers to private places where they contaminate non smokers, and in particular young children. Bans affect socio-economic groups differently: we find that smoking bans increase the exposure of poorer individuals, while it decreases the exposure of richer individuals.