Society had changed its view on smoking since 1960s. what was the major cause of this change

The 60s were the time when the act of smoking 20 or more cigarettes a day was considered normal. The states like California however led the effort to curb smoking of tobacco. In 1964, the Surgeon General of US issued a report stating that the smoking causes cancer. This led to the people giving up on their smoking habits. The major decline of smokers happened amongst the youth who had just started to smoke. Since then the society has a negative perception of smoking and its health consequences on the people nearby and on the smoker.