Cigarette smoke is a foul and obnoxious mixture of thousands of chemical compounds. This is generally an undisputed claim and the basis for banning smoking in public locations.
More than 4,000 different chemical compounds have been identified in cigarette smoke.
There are likely many more substances in cigarette smoke but they are beyond detection limits.
More than 300 of these compounds have been identified as poisonous or carcinogenic substances.
For example, approximately 4.5 per cent of cigarette smoke is carbon monoxide. This is the same material generated by automobile exhaust and other forms of combustion. It is generated by the same process - partial or incomplete combustion.
Carbon monoxide poisoning is a consequence of the binding of the molecule to the hemoglobin in blood. It is very efficient, over 250 times more efficient at binding hemoglobin than oxygen. As a consequence, it displaces oxygen in the bloodstream and produces a sense of lightheadedness at the levels in cigarettes.
However, too much carbon monoxide results in too little oxygen in the blood and can lead directly to death. Fortunately for smokers, the body is capable of defending itself against low level carbon monoxide poisoning by building more hemoglobin.
Unfortunately for smokers, this has consequences which can help exacerbate heart disease.
But aside from the poisonous carbon monoxide, cigarette smoke is a potpourri of noxious and dangerous compounds.
A single puff contains a multitude of potential carcinogens. For example, Poly-Aromatic Hydrocarbons or PAHs are large aromatic molecules that can interfere with cellular reproduction and result in mutations in DNA. Compounds such as benzo(a)anthracene and benzo(a)pyrene are capable of inserting into the ladder struck of the double helix and causing errors in replication.
Magnified, these errors can lead to nuclear damage and eventually to uncontrolled cell growth resulting in a tumor.
There are also much simpler molecules found in cigarette smoke such as ammonia, acetone, and naphthalene. Ammonia is a common household cleaning agent. Acetone is better known as nail polish remover. And naphthalene was a common ingredient in moth balls.
One of the simplest of all compounds found in cigarette smoke is hydrogen cyanide. It is extremely poisonous as it is also capable of binding irreversibly to hemoglobin. Fortunately for smokers and those around them, hydrogen cyanide levels average around 500 micrograms per puff. Not enough to kill but certainly hard on the heart.
But the drug component of cigarette smoke - nicotine - is neither a PAH nor a carcinogen. When talking to people about smoking, they often conflate nicotine with the potential harm that comes from cigarettes and look for low nicotine containing brands.
Nicotine is an alkaloid. It is a nitrogen containing compound with a very specific shape or structure.
It is a poison used in insecticides.
Indeed, its lethal dose in humans is around one part per million or about 40 to 60 milligrams for a typical adult.
It is also a mood-altering chemical. The dosage in a typical cigarette is in the microgram range per puff or about three milligrams for a whole cigarette. At this level, nicotine doesn't kill but it can travel through the bloodstream and enter the brain.
The effects of nicotine are paradoxical as it acts as both a stimulant and a relaxant. Users typically report feelings of relaxation and calmness while also feeling more alert and sharp.
Like any stimulant, nicotine also suppresses the appetite and enhances metabolic rates resulting in mild weight loss.
Weight gain is one of the big complaints from people who are trying to quit smoking.
Nicotine causes a release of glucose from the liver, elevating blood sugar levels, and epinephrine from the adrenal medulla.
It also stimulates the nicotinic acetylcholine receptors in the brain resulting in a flood of neurochemicals such as acetylcholine, norepinephrine, serotonin, and dopamine.
Nicotine also enhances the pleasure sensations arising from dopamine release while increasing the sensitivity of the brain's reward system. A little rush accompanies each puff and leads to addiction.
It is not a harmless compound.
Nicotine alters brain chemistry and while it has been demonstrated to enhance memory formation, it is hard on the body as a whole as the excess neurotransmitters tend to overstimulate a number of fundamental processes.
However, it is nicotine which smokers seek and as a consequence nicotine patches are often used as a way to gently help a smoker quit.
Ironically, nicotine's half-life in the body is very short. The chemical itself is purged in less than 12 hours. It is the damage it does which leads to the intense cravings for another cigarette. New methods of administering nicotine - through electronic cigarettes and "vaping" - do not address the fundamental nature of this addiction.
The World Health Organization estimates six million people die every year as a direct result of cigarette smoking.
