`` Nicotine is not the thing in tobacco smoke that causes cancer , but inhaling pure nicotine may be dangerous , '' said Dr. Steven Schroeder , physician and smoking cessation expert at the University of California-San Francisco Medical Center . Electronic cigarettes do n't contain tar , other chemicals ; only liquid nicotine . Comment: FDA says safety not proved , has been refusing importations . WHO called for more safety testing in 2008 .
Electronic cigarettes do n't contain tar , other chemicals ; only liquid nicotine . Comment: FDA says safety not proved , has been refusing importations . WHO called for more safety testing in 2008 .