Tobacco smoking is the practice of burning tobacco and inhaling the resulting smoke (consisting of particle and gaseous phases). The practice may have begun as early as 5000–3000 BC.  Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes. The practice encountered criticism from its first import into the Western world onwards, but embedded itself in certain strata of a number of societies before becoming widespread upon the introduction of automated cigarette-rolling apparatus.  
German scientists identified a link between smoking and lung cancer in the late 1920s, leading to the first anti-smoking campaign in modern history, albeit one truncated by the collapse of the Third Reich at the end of the Second World War.  In 1950, British researchers demonstrated a clear relationship between smoking and cancer.  Scientific evidence continued to mount in the 1980s, which prompted political action against the practice. Rates of consumption since 1965 in the developed world have either peaked or declined.  However, they continue to climb in the developing world. 
Smoking is the most common method of consuming tobacco, and tobacco is the most common substance smoked. The agricultural product is often mixed with additives  and then combusted. The resulting smoke is then inhaled and the active substances absorbed through the alveoli in the lungs.  The active substances trigger chemical reactions in nerve endings, which heighten heart rate, alertness,  and reaction time.  Dopamine and endorphins are released, which are often associated with pleasure.  As of 2000, smoking is practiced by approximately 1.22 billion people. In most communities men are more likely to smoke than are women,  though the gender gap tends to be less pronounced in lower age groups.  
Many smokers begin during adolescence or early adulthood. During the early stages, a combination of perceived pleasure acting as positive reinforcement and desire to respond to social peer pressure may offset the unpleasant symptoms of initial use, which typically include nausea and interrupted sleep patterns. After an individual has smoked for some years, the avoidance of withdrawal symptoms and negative reinforcement become the key motivations to continue.
Prostitution of children or child prostitution is the commercial sexual exploitation of children in which a child performs the services of prostitution, for financial benefit. The term normally refers to prostitution by a minor, or person under the local age of majority. In many countries there are specific laws against child prostitution which may include people who are older than the local Age of consent.
The form of child prostitution in which people travel to foreign countries for the purposes of avoiding laws in their country of residence is known as child sex tourism.
A customer may negotiate an exchange directly with a child prostitute in order to receive sexual gratification, or through an intermediary (pimp) who controls or oversees the prostitute’s activities for profit. The provision of children for sexual purposes may also be an object of exchange between adults. Many children are prostituted over the Internet with the use of webcams to facilitate this abuse, and child pornography may be linked to the prostitution.