Smoking and cancer: What's in a cigarette?
A cigarette may look harmless
enough - tobacco leaves covered in classic white paper. But when it burns, it
releases a dangerous cocktail of about 4,000 chemicals including:
at least
80 cancer-causing chemicals
hundreds
of other poisons.
nicotine,
a highly addictive drug, and many additives designed to make cigarettes taste
nicer and keep smokers hooked.
This page has more information
on the various poisons in cigarette smoke. You can also read about where these
come from and how concentrated they actually are.
Cancer-causing chemicals in
tobacco smoke
Tar - a mixture of dangerous chemicals
Arsenic - used in wood preservatives
Benzene - an industrial solvent, refined from crude
oil
Cadmium - used in batteries
Formaldehyde - used in mortuaries and paint
manufacturing
Polonium-210 - a highly radioactive element
Chromium - used to manufacture dye, paints and alloys
1,3-Butadiene - used in rubber manufacturing
Polycyclic aromatic hydrocarbons - a group of
dangerous DNA-damaging chemicals
Nitrosamines - another group of DNA-damaging chemicals
Acrolein - formerly used as a chemical weapon
Other chemicals
Other poisons in cigarette
smoke
Hydrogen cyanide - used as an industrial pesticide
Carbon monoxide - found in car exhausts and used in
chemicals manufacturing
Nitrogen oxides - a major component of smog
Ammonia - used to make fertilisers and explosives
More poisons
Tar
Tar is a term that describes a
collection of solid particles that smokers inhale when they light a cigarette.
It is a mixture of lots of chemicals, many of which can cause cancer. When it
settles, tar forms a sticky, brown residue that can stain smokers’ teeth,
fingers and lungs.
Because tar is listed on packs,
it is easy to believe that it is the only harmful part of cigarettes. But some
of the most dangerous chemicals in tobacco smoke are present as gases, and do
not count as part of tar. This means that cigarettes with less tar still
contain all the other toxic chemicals.
Arsenic
Arsenic
is one of the most dangerous chemicals in cigarettes. It can cause cancer as
well as damaging the heart and its blood vessels.
Small amounts of arsenic can
accumulate in smokers’ bodies and build up to higher concentrations over months
and years. As well as any direct effects, it can worsen the effect of other
chemicals by interfering with our ability to repair our DNA.
Fish and seafood can be major
sources of arsenic, but in a form that is less toxic and more readily removed
from the body. In contrast, tobacco smoke contains arsenic in a more dangerous
form.
Benzene
Benzene is a solvent used to
manufacture other chemicals, including petrol. It is well-established that
benzene can cause cancer, particularly leukaemia. It could account for between
a tenth and a half of the deaths from leukaemia caused by smoking.
Tobacco smoke contains large
amounts of benzene and accounts for a big proportion of our exposure to this poison.
The average smoker inhales about ten times more benzene than the average
non-smoker.
And some studies have estimated
that the amount of benzene that a person inhales through second-hand smoke over
their lifetime could increase their risk of cancer.
Cadmium
Cadmium is a metal used mostly
to make batteries. The majority of cadmium in our bodies comes from exposure to
tobacco smoke. Smokers can have twice as much cadmium in their blood as
non-smokers.
Studies have found that the
amounts of cadmium present in tobacco smoke are capable of affecting our
health. It is a known cause of cancer, and can also damage the kidneys and the
linings of the arteries.
Our bodies have proteins that
mop up harmful chemicals like cadmium, but the amounts in smoke can overload
these proteins. Cadmium can also prevent our cells from repairing damaged DNA.
Because of this, it can make the effects of other chemicals even worse.
Formaldehyde
Formaldehyde is a smelly
chemical used to kill bacteria, preserve dead bodies and manufacture other
chemicals. It is one of the substances in tobacco smoke most likely to cause
diseases in our lungs and airways.
Formaldehyde is also a known
cause of cancer. It is believed that even the small amounts in second-hand
smoke could increase our lifetime risk of cancer.
Tobacco smoke is one of our
major sources of formaldehyde exposure. Places where people smoke can have
three times the normal levels of this poison.
Polonium-210
Polonium is a rare, radioactive
element and polonium-210 is its most common form. Polonium strongly emits a
very damaging type of radiation called alpha-radiation that can usually be
blocked by thin layers of skin.
But tobacco smoke contains
traces of polonium, which become deposited inside their airways and deliver
radiation directly to surrounding cells. The lungs of smokers can be exposed to
four times more polonium than those of non-smokers and specific parts may get a
hundred times more radiation. One study estimated that someone smoking one and
half packs a day receives the equivalent amount of radiation as someone having
300 chest X-rays a year.
Chromium
Chromium is a metal used to
make metallic alloys, dyes and paints and comes in different types. Chromium
III or ‘trivalent chromium’ is most commonly used. It is available as dietary
supplements and is harmless.
On the other hand, chromium VI
or ‘hexavalent chromium’ is very toxic, is found in tobacco smoke, and is known
to cause lung cancer. It allows other cancer-causing chemicals (such as
polycyclic aromatic hydrocarbons) to stick more strongly to DNA and damage it.
1,3-Butadiene
1,3-butadiene or BDE is an
industrial chemical used in rubber manufacture. Some scientists believe that of
all the chemicals in tobacco smoke, BDE may present the greatest overall cancer
risk. It may not be as good at causing cancer as some of the other chemicals
listed here, but it is found in large amounts in tobacco smoke.
Polycyclic aromatic
hydrocarbons
Polycyclic aromatic
hydrocarbons or PAHs are a group of powerful cancer-causing chemicals that
candamage DNA and set cells down the road to becoming tumours.
One of these chemicals -
benzo(a)pyrene or BAP - is one of the most widely studied of all tobacco
poisons. BAP directly damages p53, a gene that normally protects our bodies
against cancer.
Nitrosamines
Nitrosamines are a group of
chemicals that can directly damage DNA, like polycyclic aromatic hydrocarbons
(PAHs).
They are found in small amounts
in food. But tobacco products, including those that are chewed rather than
smoked, are by far our largest source of exposure to these chemicals. Even
though they are found in relatively small amounts in cigarettes, they are very
strong cancer-causing chemicals.
Acrolein
Acrolein is a gas with an
intensely irritating smell and is one of the most abundant chemicals in
cigarette smoke. It belongs to the same group of chemicals as formaldehyde and
acetaldehyde, both of which can cause cancer.
Until now, it wasn’t clear if
acrolein causes cancer as well, but recent experiments suggest that it can. We
now know that acrolein can cause DNA damage that is similar to the damage seen
in lung cancer patients. Since smoke contains up to 1,000 times more acrolein
than other DNA-damaging chemicals, it could be a major cause of lung cancer.
Acrolein also stops our cells
from repairing DNA damage, like arsenic and cadmium. And like hydrogen cyanide,
it kills the hairs that normally clean our lungs of other toxins.
Other chemicals
Some of the other
cancer-causing ingredients of tobacco smoke include:
metals, such as nickel, lead, cobalt and
beryllium. While you may be exposed to some of these metals through
domestic items or food, inhaling them in tobacco smoke is worse, because they
are easily absorbed by the lungs.
acetaldehyde,
which is also formed in your tissues when you drink alcohol - it is responsible
for many nasty hangover symptoms
hydrazine, a
very toxic chemical used mainly in rocket fuel
Hydrogen cyanide
Hydrogen cyanide is a poisonous
gas. Of all the chemicals in tobacco smoke, it does the most damage to the
heart and blood vessels.
Hydrogen cyanide does not cause
cancer, but it increases the risk of other chemicals causing cancer by damaging
cilia. These are tiny hairs lining the airways that help to clear toxins away.
By killing cilia, hydrogen cyanide causes other dangerous chemicals to be stuck
in the lungs and airways.
Carbon monoxide
Carbon monoxide is a colourless
gas with no smell. It is formed when we burn carbon-based fuels, such as gas in
cookers or petrol in car engines. It can make up as much as 3-5% of tobacco
smoke.
Carbon monoxide sticks to our
red blood cells in place of oxygen. This lowers our blood’s ability to
transport oxygen and deprives our tissues and organs of this vital gas.
Like hydrogen cyanide, it kills
cilia and reduces our lungs’ ability to clear away toxins. This means that
while carbon monoxide does not cause cancer directly, it makes it easier for
other chemicals to do so.
Nitrogen oxide
Nitrogen oxide is a gas found
in car exhaust and tobacco smoke.
Our bodies use it in very small
amounts to carry signals between cells. But in large amounts, it is a major air
pollutant. It directly damages lung tissue and causes inflammation in the
lungs.
Normally, our bodies produce
small amounts of nitrogen oxide, which causes our airways to expand. The large
amount of nitrogen oxide in tobacco smoke changes things in two ways:
When smokers are smoking, it expands their airways
even further, making it easier for their lungs to absorb nicotine and other
chemicals.
When they are not smoking, it shuts off their internal
nitrogen oxide production line, causing their airways to constrict. This is one
reason why regular smokers often have difficulty breathing.
Ammonia
Ammonia is a gas with a strong,
irritating smell, and is used in some toilet cleaners. Some studies have found
that ammonia enhances the addictive power of nicotine. It changes nicotine into
a gas that is more readily absorbed into the lungs, airways and bloodstream.
Like carbon monoxide and
hydrogen cyanide, ammonia also kills cilia.
More poisons
Tobacco smoke also contains
many other poisons that produce harmful effects. These can be carried
throughout the body via our blood vessels. As well as hydrogen cyanide and
ammonia, gases like sulphur dioxide also kill cilia (protective hairs)
in our lungs. This stops them from being able to clear away other harmful chemicals.
Chemicals like hydrogen
sulphide and pyridine irritate our airways.
Toluene can damage brain cells and interfere
with their development.
