Smoke from the lit end of a cigarette has higher concentrations of carcinogens and nicotine compared to cigarette smoke exhaled from the lungs of a smoker.
This is because freshly lit tobacco smoke from the lit end of the cigarette will produce high levels of post-combustion compounds (i.e. carbon monoxide, tar, etc.) and these compounds are highly carcinogenic. Nicotine levels are also higher in the lit end of a cigarette.