Smoking didn't exist during the time of the Prophet S.A.W. and so the scholars followed the same principle of the thick dust, because if a person is inhaling that smoke from his/her cigarette or shisha, this person is taking in a large amount of smoke, which is made up of dust and particles and therefore he/she is doing the exact same action as breathing in thick dust, thus this person is breaking there fast. however, there a few scholars that are unique in this ruling and went out of the ordinary ruling by saying that smoking does not break their fast, saying there is no evidence, but out of precaution it is advised that one should not smoke during ones fast. one possible reason for such a ruling is that as when a person is inhaling air it is going into the airways and not the digestive system nor the oesophagus and therefore it does not have the same effect as thick dust but now me must ask medical professionals if that is the case and then make the judgement.