Airlines may have their own restrictions, but I have found this page on the TSA website with TSA rules to be very helpful (these are for domestic flights, international flights may vary)
Aerosols (vapor) emitted by e-cigarettes contain ultrafine particles, such as volatile carbonyls, formaldehyde, acetaldehyde, acrolein, and acetone, all of which have established negative health effects 6
And at the end of six months without smoking, a new consultation is scheduled for six months later. After a year without smoking, patients are considered to be former smokers and will only come back for a consultation a year later
Cartoon Characters "Smooth" cartoon characters such as Joe Camel were deployed to appeal to young audiences at an impressionable age
Medical doctors and academic scholars were hired to defend the industrys claim that the evidence was merely statistical or based only on animal evidence