Tobacco smoke is a mixture of gases and small particles made up of water, tar and nicotine. The tar is a messy mixture of hundreds of toxic chemicals, many of which are known to cause cancer (for example, nitrosamines, benzpyrene).
Many of the gases in tobacco smoke are harmful. These include carbon monoxide, nitrogen oxides, hydrogen cyanide, ammonia, and other toxic irritants such as acrolein and formaldehyde. Due to the high temperatures (over 800°C or 1400°F), the burning end of a cigarette is like a miniature chemical factory. It churns out many more noxious chemicals than are found in unlit tobacco or taken in by use of smokeless tobacco (for example, snuff, which contains no tar or gases). Altogether more than 4,000 chemical compounds have been identified in tobacco smoke.
The chemicals that cause cancer are mainly in the tar. Tar, together with some of the irritant gases, may also be partly responsible for chronic bronchitis and emphysema. Nitrogen oxides are suspected, but the main agents responsible are not yet known. Neither nicotine nor carbon monoxide causes cancer, but they probably work together as causes of the heart diseases associated with smoking.
It is easy to understand why the main cancers caused by smoking are at sites having direct contact with the smoke, specifically the lungs, mouth, and throat. However, some cancer-producing chemicals are absorbed into the blood and transported to other parts of the body. This is how smoking causes cancer of the bladder, kidney, pancreas, and uterus.
The way in which smoking causes heart attacks, strokes and other cardiovascular diseases is quite complex.
After absorption through the lungs, carbon monoxide combines with hemoglobin in the red blood cells and reduces the amount of oxygen they can carry around the body.
Carbon monoxide and nicotine both appear to play a part in accelerating the deposition of cholesterol in the inner lining of arteries which over many years leads to arteriosclerosis, a kind of hardening and furring up of arteries which reduces blood flow.
Cigarette smoking also makes the blood clot more easily, making episodes of thrombosis more likely.
Impairment of blood flow, and of oxygen-carrying capacity due to carbon monoxide, all reduce the supply of oxygen. This happens at the same time that the heart's need for oxygen is increased by the stimulant effect of nicotine on the rate and force of the heart's contractions.
The lack of oxygen is damaging to the heart and increases the severity of a heart attack.
Nicotine can cause further problems by upsetting the regular rhythm of the heart.
Nicotine and carbon monoxide are also important factors in peripheral vascular disease, which can lead to gangrene of the feet. Nicotine causes constriction, or narrowing, of the small blood vessels. This, combined with carbon monoxide's oxygen-reducing effect, tips the balance in people with narrowed leg arteries.
Likewise, nicotine constriction of blood vessels in the placenta (which provides nourishment to an unborn baby), combined with the effects of carbon monoxide, reduces oxygen supply to the unborn babies of pregnant women who smoke.
In these various ways both nicotine and carbon monoxide are involved in the effects of smoking on coronary heart disease, other vascular diseases, and on the development of the unborn child. Although stopping smoking may not reverse arteriosclerosis, a disease in which plaque builds up in the arteries, it will progress less quickly.
However, the other negative effects from smoking are reversed within 24 hours of stopping, when nicotine and carbon monoxide have cleared from the body.
Nice To Know:
Within 48 hours after quitting smoking, blood pressure decreases, pulse rate drops, body temperature of hands and feet increases, the carbon monoxide level in the blood returns to normal, the oxygen level in the blood increases to normal, the chance of a heart attack decreases, nerve endings start regrowing, and the ability to taste and smell is increased.
Within the first year after quitting smoking circulation and lung function increase, and coughing, sinus congestion and shortness of breath decrease.
About Low-Tar Cigarettes
The average yield of U.S. cigarettes is about 12 mg tar, .88 mg nicotine, and 14 mg carbon monoxide.
Cigarette brands having tar yields below 10 mg are labeled low-tar, and their yields of nicotine and carbon monoxide also tend to be low.
Only one in five smokers regularly smokes a low-tar brand. Many smokers find them unsatisfying at first and do not persist long enough to get used to them. A few ultra-low yield brands exist (tar below 3 mg, nicotine below 0.3 mg).
Due to continuous changes in cigarettes over the years and the time taken for smoking-related diseases to develop, it has been difficult to prove that low-tar cigarettes are less harmful. This remains controversial.
Despite the tendency for smokers to compensate for lower yields by puffing and inhaling harder, the compensation is usually incomplete. On average, blood nicotine and carbon monoxide levels are reduced by at least 10 to 15 percent after switching to low-tar cigarettes. It is therefore likely that they are also less harmful.
Pipe And Cigar Smoking
Pipe and cigar smokers who have never smoked cigarettes tend to be non-inhalers and their health risks are not as great as those of cigarette smokers. Due to the stronger, more alkaline smoke and longer periods of puffing, satisfying amounts of nicotine are absorbed slowly through the lining of the mouth and throat. However, their risk for cancers of the mouth and throat are significantly higher than that of nonsmokers.
Cigarettes, in contrast, provide pharmacological doses of nicotine only if they are inhaled. Cigarette smokers unfortunately become so addicted to the rapid absorption of nicotine through the lungs that they usually continue to inhale after switching to a pipe or cigars. Their health risks are therefore not reduced after switching and may even be increased. By providing smaller and milder cigars, the tobacco industry has made it easier for smokers to continue to inhale when they switch to cigars.
Passive smoking is the breathing in of air that has been polluted by other people's smoke. The smoke and the chemicals it contains remain in the air of a room for many hours, especially if it is poorly ventilated. They can also spread to other rooms.
The concentrations of some cancer-producing nitrosamines are much higher in the side-stream smoke from the burning end of a cigarette than in the mainstream smoke inhaled directly by the smoker.
Passive smoking is difficult to avoid completely, and most nonsmokers who are exposed to it have measurable quantities of smoke products in their body fluids. Many nonsmokers find other people's smoke unpleasant and irritating. It may give them headaches and feelings of hangover.
Passive smoke also carries significant health risks for nonsmokers:
The amount of nicotine absorbed by a nonsmoking child whose father smokes is equivalent to the child himself smoking about 30 cigarettes a year; 50 cigarettes a year from a mother who smokes, and 80 cigarettes a year if both parents smoke.
A nonsmoker who spends about four hours in a smoky room may absorb the equivalent of one cigarette.
Nonsmoking women whose husbands smoke have a 50% increase in their risk for lung cancer.
Secondhand smoke causes about 3,000 lung cancer deaths each year in nonsmokers.
Young children are especially vulnerable and have an increased risk of coughs and chest and ear infections if their parents smoke.