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Our nose, mouth and throat contain nerve endings that sense painful and irritating chemicals in the inhaled air. For example, the burning, stinging feeling elicited by smoke inhalation is mediated by these nerve endings. They also trigger sneezing and cough, basically to defend the lungs from inhaling toxic chemicals, the new chemicals we identified in e-cigarettes activate these nerve endings more strongly. Especially when activated over a longer period, as in smokers, and potentially in e-cigarette users, these mechanisms have been shown to cause inflammation and asthma and contribute to emphysema.