Scientific evidence of the health risks posed by smoking go back to the 1950s. Figures from the US government show that 28% of males 18 years old and above and 23% of females in the same age bracket were into the habit in the mid-1990s. The percentages were even higher in 1964, when the US surgeon general first issued an official warning that smoking was hazardous to one's health.

Following that formal warning, many reports were released on the link between cigarettes and tobacco to heart diseases, lung diseases, and cancers of the mouth and other tissues. However, the habit persisted, with young smokers doing so as an expression of rebellion and strong drive to be independent.

For adults, smoking marked an addiction to nicotine - the key factor that made smoking a pleasurable and addictive experience. This led to another warning from the surgeon general in 1988, which put addiction to nicotine on the same level as cocaine and heroin.

The danger in smoking comes from the chemical substances released either as a gas or as a particulate. Nitrogen oxides, hydrogen cyanide and most especially carbon monoxide are gaseous emissions from cigarette smoke that threaten to poison the body.

Nicotine is one of several hazardous particulates emitted from smoking. These particulates damage the cilia - the little hairs lining the lungs that help transport mucus out of the lungs, and all pollutants accumulated. When the cilia malfunction, pollutants remain in the lungs and the likelihood of influenza and bronchitis, emphysema and other diseases increases.

The possibility that smokers die from cancer and heart disease is twice that of their non-smoking counterparts. Individuals who smoke also have lungs that become less efficient with age much faster than those who don't. Smoking has been cited as the cause of over 400,000 deaths in the US every year.

Government agencies, scientists and health officials have also established that passive smoking, or second-hand smoke, also has ill effects. The National Center for Chronic Disease Prevention and Health Promotion has reported that over 4,000 chemicals are generated by second-hand smoke, with more than 50 of those believed to be cancer-causing agents.

In 1975, the Centers for Disease Control released a report citing such a danger, noting that toxic chemicals stay in the air and are inhaled by unsuspecting victims. Thus, the concern over smoking as a private choice by individuals expanded into a public-health issue.

Passive smoking was cited as a cancer-causing agent by the US Environmental Protection agency in 1993. For pregnant women, smoking raises the chances that their baby will be underweight or that they end up with a miscarriage. Children less than a year old are twice as likely to have lung infections if their mothers smoke compared to counterparts whose mothers do not practice the habit. Individuals with asthma, allergies or other respiratory ailments were also warned, as exposure can worsen their conditions.

Some smokers gradually quit or smoked less, while nonsmokers became the focus of more protection, as government worked on policies and legislation to curb the habit. As early as 1964, the US signed into law a requirement that health warnings must be integrated into all cigarette advertising and packaging. Policies were also implemented to designate schools, offices and other public places as smoke-free buildings.

In the 1990s, class action suits started to bombard state and federal courts, claiming that cigarette makers employed deceptive marketing tactics to keep consumers from knowing that nicotine was addictive and worked on levels of the particulate in cigarettes to keep smokers hooked on their product.

More recent suits against the industry charge manufacturers of also misleading consumers into thinking that "lights" and similar products were healthier alternatives to regular cigarettes. These more recent cases later led to the multi-billion dollar settlement between the US government and industry in the late 1990s.

These lawsuits and the consistency of health lobbyists and persuasive government programs have helped pull down US smoking rates on a consistent basis over the last four decades, with government figures showing per capita rates at 22.5% and experts forecasting the rates to continue declining in the future.