It is commonly an unwanted by-product of fires (including stoves, candles, internal combustion engines, oil lamps, and fireplaces), but may also be used for pest control (fumigation), communication (smoke signals), defensive and offensive capabilities in the military (smoke screen), cooking, or smoking (tobacco, cannabis, etc.)
It's most often associated with smoking, but other factors such as air pollution and genetics can contribute
Heavy smokers and ex smokers often find cigalikes helpful for quitting smoking because they feel like a real cigarette, making the transition smoother and more familiar
In one region, there was heterogeneity in referral rates between suburbs, which appeared to be driven by individual GP clinics referring more than others [22]