Take a minute to go through the process of LUNG ATTACK presented by Air Info Now.
http://www.airinfonow.org/html/lungattack/lungplay.htm
In contrast to smoke particles, gases emitted by the cigarette such as benzene and carbon monoxide (CO) are invisible to the eye. Particles smaller than 2.5 micrometers (PM2.5) are major components of cigarette smoke and can enter deep into the lung where they can cause serious health problems.