its flavors. most commercially available cigarettes today contain tobacco that is treated with sugar to counter the harshness of the smoke. additives various additives are combined into the shredded tobacco product mixtures, with humectants such as propylene glycol or glycerol, as well as flavoring products and enhancers such as cocoa solids, licorice, tobacco extracts, and various sugars, which are known collectively as "casings". the leaf tobacco is then shredded, along with a specified amount of small laminate, expanded tobacco, bl, rl, es, and is. a perfume-like flavor/fragrance, called the "topping" or "toppings", which is most often formulated by flavor companies, is then blended into the tobacco mixture to improve the consistency in flavor and taste of the cigarettes associated with a certain brand name. additionally, they replace lost flavors due to the repeated wetting and drying used in processing the tobacco. finally, the tobacco mixture is filled into cigarette tubes and packaged. a list of 599 cigarette additives, created by five major american cigarette companies, was approved by the department of health and human services in april 1994. none of these additives is listed as an ingredient on the cigarette pack(s). chemicals are added for organoleptic purposes and many boost the addictive properties of cigarettes, especially when burned. one of the classes of chemicals on the list, ammonia salts, convert bound nicotine molecules in tobacco smoke into free nicotine molecules. this process, known as freebasing, could potentially increase the effect of nicotine on the smoker, but experimental data suggests that absorption is, in practice, unaffected. cigarette tube cigarette tubes are prerolled cigarette paper usually with an acetate or paper filter at the end. they have an appearance similar to a finished cigarette, but are without any tobacco or smoking material inside. the length varies from regular (70 mm) to king size (84 mm) as well as 100s (100 mm) and 120s (120 mm). filling a cigarette tube is usually done with a cigarette injector (also known as a shooter). cone-shaped cigarette tubes, known as cones, can be filled using a packing stick or straw because of their shape. cone smoking is popular because as the cigarette burns, it tends to get stronger and stronger. a cone allows more tobacco to be burned at the beginning than the end, allowing for an even flavor the united states tobacco taxation bureau defines a cigarette tube as "cigarette paper made into a hollow cylinder for use in making cigarettes." cigarette filter a cigarette filter or filter tip is a component of a cigarette. filters are typically made from cellulose acetate fibre. most factory-made cigarettes are equipped with a filter; those who roll their own can buy them separately. filters can reduce some substances from smoke but do not make cigarettes any safer to smoke. cigarette butt a discarded cigarette butt, lying on dirty snow the common name for the remains of a cigarette after smoking is a cigarette butt. the butt is typically about 30% of the cigarette's original length. it consists of a tissue tube which holds a filter and some remains of tobacco mixed with ash. they are the most numerically frequent litter in the world. cigarette butts accumulate outside buildings, on parking lots, and streets where they can be transported through storm drains to streams, rivers, and beaches. it is also called a fag-end or dog-end. in a 2013 trial, the city of vancouver, british columbia, partnered with terracycle to create a system for recycling of cigarette butts. a reward of 1¢ per collected butt was offered to determine the effectiveness of a deposit system similar to that of beverage containers. electronic cigarette main article: electronic cigarette further information: safety of electronic cigarettes and composition of electronic cigarette aerosol various types of electronic cigarettes an electronic cigarette is a handheld battery-powered vaporizer that simulates smoking by providing some of the behavioral aspects of smoking, including the hand-to-mouth action of smoking, but without combusting tobacco. using an e-cigarette is known as "vaping" and the user is referred to as a "vaper". instead of cigarette smoke, the user inhales an aerosol, commonly called vapor. e-cigarettes typically have a heating element that atomizes a liquid solution called e-liquid. e-cigarettes are automatically activated by taking a puff; others turn on manually by pressing a button. some e-cigarettes look like traditional cigarettes, but they come in many variations. most versions are reusable, though some are disposable. there are first-generation, second-generation, third-generation, and fourth-generation devices. e-liquids usually contain propylene glycol, glycerin, nicotine, flavorings, additives, and differing amounts of contaminants. e-liquids are also sold without propylene glycol, nicotine, or flavors. the benefits and the health risks of e-cigarettes are uncertain. there is moderate-certainty evidence that e-cigarettes with nicotine may help people quit smoking when compared with e-cigarettes without nicotine and nicotine replacement therapy. however, other studies have not supported the finding that e-cigarettes are proven to be more effective than smoking cessation medicine. there is concern with the possibility that non-smokers and children may start nicotine use with e-cigarettes at a rate higher than anticipated than if they were never created. following the possibility of nicotine addiction from e-cigarette use, there is concern children may start smoking cigarettes. youth who use e-cigarettes are more likely to go on to smoke cigarettes. their part in tobacco harm reduction is unclear, while another review found they appear to have the potential to lower tobacco-related death and disease. regulated us food and drug administration nicotine replacement products may be safer than e-cigarettes, but e-cigarettes are generally seen as safer than combusted tobacco products. it is estimated their safety risk to users is similar to that of smokeless tobacco. the long-term effects of e-cigarette use are unknown. the risk from serious adverse events was reported in 2016 to be low. less serious adverse effects include abdominal pain, headache, blurry vision, throat and mouth irritation, vomiting, nausea, and coughing. nicotine itself is associated with some health harms. in 2019 and 2020, an outbreak of severe lung illness throughout the us was linked to the use of vaping products e-cigarettes create vapor made of fine and ultrafine particles of particulate matter, which have been found to contain propylene glycol, glycerin, nicotine, flavors, small amounts of toxicants, carcinogens, and heavy metals, as well as metal nanoparticles, and other substances. its exact composition varies across and within manufacturers, and depends on the contents of the liquid, the physical and electrical design of the device, and user behavior, among other factors. e-cigarette vapor potentially contains harmful chemicals not found in tobacco smoke. e-cigarette vapor contains fewer toxic chemicals, and lower concentrations of potential toxic chemicals than cigarette smoke. the vapor is probably much less harmful to users and bystanders than cigarette smoke, although concern exists that the exhaled vapor may be inhaled by non-users, particularly indoors. health effects smokers main article: health effects of tobacco artistas brand cigarette package of mexico from the museo del objeto del objeto collection the harm from smoking comes from the many toxic chemicals in the natural tobacco leaf and those formed in smoke from burning tobacco. people keep smoking because the nicotine, the primary psychoactive chemical in cigarettes, is highly addictive. cigarettes, like narcotics, have been described as "strategically addictive", with the addictive properties being a core component of the business strategy. about half of smokers die from a smoking-related cause. smoking harms nearly every organ of the body. smoking leads most commonly to diseases affecting the heart, liver, and lungs, being a major risk factor for heart attacks, strokes, chronic obstructive pulmonary disease (copd) (including emphysema and chronic bronchitis), and cancer (particularly lung cancer, cancers of the larynx and mouth, and pancreatic cancer). it also causes peripheral vascular disease and hypertension. children born to women who smoke during pregnancy are at higher risk of congenital disorders, cancer, respiratory disease, and sudden death. on average, each cigarette smoked is estimated to shorten life by 11 minutes. starting smoking earlier in life and smoking cigarettes higher in tar increases the risk of these diseases. the world health organization estimates that tobacco kills 8 million people each year as of 2019 and 100 million deaths over the course of the 20th century. cigarettes produce an aerosol containing over 4,000 chemical compounds, including nicotine, carbon monoxide, acrolein, and oxidant substances. over 70 of these are carcinogens. the most important chemical compounds causing cancer are those that produce dna damage since such damage appears to be the primary underlying cause of cancer. cunningham et al. combined the microgram weight of the compound in the smoke of one cigarette with the known genotoxic effect per microgram to identify the most carcinogenic compounds in cigarette smoke. the seven most important carcinogens in tobacco smoke are shown in the table, along with dna alterations they cause. the most genotoxic cancer causing chemicals in cigarette smoke compound micrograms per cigarette effect on dna ref. acrolein 122.4 reacts with deoxyguanine and forms dna crosslinks, dna-protein crosslinks and dna adducts formaldehyde 60.5 dna-protein crosslinks causing chromosome deletions and re-arrangements acrylonitrile 29.3 oxidative stress causing increased 8-oxo-2'-deoxyguanosine 1,3-butadiene 105.0 global loss of dna methylation (an epigenetic effect) as well as dna adducts acetaldehyde 1448.0 reacts with deoxyguanine to form dna adducts ethylene oxide 7.0 hydroxyethyl dna adducts with adenine and guanine isoprene 952.0 single and double strand breaks in dna "ulcerative colitis is a condition of nonsmokers in which nicotine is of therapeutic benefit." a recent review of the available scientific literature concluded that the apparent decrease in alzheimer disease risk may be simply because smokers tend to die before reaching the age at which it normally occurs. "differential mortality is always likely to be a problem where there is a need to investigate the effects of smoking in a disorder with very low incidence rates before age 75 years, which is the case of alzheimer's disease", it stated, noting that smokers are only half as likely as nonsmokers to survive to the age of 80. gateway theory a very strong argument has been made about the association between adolescent exposure to nicotine by smoking conventional cigarettes and the subsequent onset of using other dependence-producing substances. strong, temporal, and dose-dependent associations have been reported, and a plausible biological mechanism (via rodent and human modeling) suggests that long-term changes in the neural reward system take place as a result of adolescent smoking. adolescent smokers of conventional cigarettes have disproportionately high rates of comorbid substance use, and longitudinal studies have suggested that early adolescent smoking may be a starting point or "gateway" for substance use later in life, with this effect more likely for persons with attention deficit hyperactivity disorder (adhd). although factors such as genetic comorbidity, innate propensity for risk-taking, and social influences may underlie these findings, both human neuroimaging and animal studies suggest a neurobiological mechanism also plays a role. in addition, behavioral studies in adolescent and young adult smokers have revealed an increased propensity for risk-taking, both generally and in the presence of peers, and neuroimaging studies have shown altered frontal neural activation during a risk-taking task as compared with nonsmokers. in 2011, rubinstein and colleagues used neuroimaging to show decreased brain response to a natural reinforcer (pleasurable food cues) in adolescent light smokers (1–5 cigarettes per day), with their results highlighting the possibility of neural alterations consistent with nicotine dependence and altered brain response to reward even in adolescent low-level smokers. second-hand smoke second-hand smoke is a mixture of smoke from the burning end of a cigarette and the smoke exhaled from the lungs of smokers. it is involuntarily inhaled, lingers in the air for hours after cigarettes have been extinguished, and can cause a wide range of adverse health effects, including cancer, respiratory infections, and asthma. nonsmokers who are exposed to second-hand smoke at home or work increase their heart disease risk by 25–30% and their lung cancer risk by 20–30%. second-hand smoke has been estimated to cause 38,000 deaths per year, of which 3,400 are deaths from lung cancer in nonsmokers. sudden infant death syndrome, ear infections, respiratory infections, and asthma attacks can occur in children who are exposed to second-hand smoke. scientific evidence shows that no level of exposure to second-hand smoke is safe. legislation smoking restrictions many governments impose restrictions on smoking tobacco, especially in public areas. the primary justification has been the