E-cigarettes remain controversial because the scientific evidence of short term and long term effects on tolerance and the health value of a switch from tobacco to e-cigarettes is contested and controversial. Nevertheless the quality of e-cigarettes and e-liquids has improved. The main ingredients, propylene glycol, vegetable glycerine and nicotine are pharmaceutical-grade quality in most e-liquids. Flavors are almost all food grade. The high quality of ingredients has decreased the presence of impurities in e-liquids. The emissions of e-cigarettes do not contain solid particles or carbon monoxide. Nitrosamine content is at least one hundred times lower than in tobacco smoke. E-cigarette emissions in normal use do not contain any harmful constituents at significant levels except nicotine. UK public health authorities have stated that e-cigarette use is likely to be at least 95% less toxic than cigarette use. There are benefits from having a well-regulated legal market. In countries where e-liquid containing nicotine is not allowed, "do-it-yourself" liquids are common and have handling risks and may sometimes contain toxic impurities. Though e-cigarettes should never be assumed safe products for non-smokers, for smokers, the e-cigarette is at least 20 times less dangerous than the cigarette. Tobacco cessation specialists in countries where nicotine containing e-cigarettes are available increasingly provide counselling for e-cigarette use to stop smoking or to reduce smoking at the request of patients. Based on current knowledge, for patients with lung or other forms of cancer who would otherwise continue to smoke, e-cigarettes offer an alternative way to quit smoking while they undergo medical treatment. (C) 2016 Elsevier Ireland Ltd. All rights reserved.