Health
effects of smoke
The effects of smoke range from eye and
respiratory tract irritation to more serious disorders, including reduced lung
function, bronchitis, exacerbation of asthma, and premature death. Studies have
found that fine particles are linked (alone or with other pollutants) with
increased mortality and aggravation of pre-existing respiratory and
cardiovascular disease. In addition, particles are respiratory irritants, and
exposures to high concentrations of particulate matter can cause persistent
cough, phlegm, wheezing, and difficulty breathing. Particles can also affect
healthy people, causing respiratory symptoms, transient reductions in lung
function, and pulmonary inflammation. Particulate matter can also affect the
body’s immune system and the physiological mechanisms that remove inhaled
foreign materials from the lungs, such as pollen and bacteria. As noted
earlier, particulate matter exposure is the principal public health threat from
short-term exposures to wildfire smoke.
Carbon monoxide (CO) enters the bloodstream through the lungs and reduces
oxygen delivery to the body’s organs and tissues. CO concentrations typical of
population exposures related to wildfire smoke do not pose a significant
hazard, except to some sensitive individuals and to firefighters very close to
the fire line. Individuals who may experience health effects from lower levels
of CO are those who have cardiovascular disease: they may experience chest pain
and cardiac arrhythmias. At higher levels (such as those that occur in major
structural fires), CO exposure can cause headache, weakness, dizziness,
confusion, nausea, disorientation, visual impairment, coma, and death, even in
otherwise healthy individuals.
Wildfire smoke
also contains significant quantities of respiratory irritants, which can act in
concert to produce eye and respiratory irritation and potentially exacerbate
asthma. Formaldehyde and acrolein are two of the principal contributors to the
cumulative irritant properties of smoke.
One concern that may be
raised by members of the general public is whether they run an increased risk
of cancer or of other chronic health conditions (e.g. heart disease) from
short-term exposure to wildfire smoke. People exposed to toxic air pollutants
at sufficient concentrations and durations may have slightly increased risks of
cancer or of experiencing other chronic health problems. However, in general,
the long-term risks from short-term smoke exposures are quite low. Short-term
elevated exposures to wildfire carcinogens are also small relative to total
lifetime exposures to carcinogens in diesel exhaust and other combustion
sources. Epidemiological studies have shown that urban firefighters exposed to
smoke over an entire working lifetime have about a threefold increased risk of
developing lung cancer (Hansen 1990). This provides some
perspective on
the magnitude of potential risks from short-term wildfire events. The major
known carcinogenic components of smoke are polycyclic aromatic hydrocarbons
(PAHs). Although other known carcinogens, such as benzene and formaldehyde, are
also present in smoke, they are thought to present a lesser risk.
Not everyone who is
exposed to thick smoke will have health problems. The level and duration of
exposure, age, individual susceptibility, including the presence or absence of
pre-existing lung or heart disease, and other factors play significant roles in
determining whether someone will experience smoke-related health problems.
Sensitive populations
Most healthy adults and
children will recover quickly from smoke exposure and will not suffer long-term
consequences. However, certain sensitive populations may experience more severe
short-term and chronic symptoms. Much of the information about how particulate
matter affects these groups has come from studies involving airborne particles
in cities, though a few studies examining the effects of exposure to smoke
suggest that the health effects of wildfire smoke are likely to be similar
(Naeher et al. 2007). More research is needed to determine whether particles
from wildfires affect susceptible subpopulations differently.
Individuals with asthma and other respiratory diseases. More than 35 million people in the US suffer from chronic lung
diseases such as asthma and chronic obstructive pulmonary disease (COPD)
(American Lung Association 2008). Levels of pollutants that may not affect
healthy people may cause breathing difficulties for people with asthma, COPD,
or other chronic lung diseases. Asthma is a condition characterized by chronic
inflammation of the bronchi and smaller airways, with intermittent airway
constriction, causing shortness of breath, wheezing, chest tightness, and
coughing, sometimes accompanied by excess mucus production. During an asthma
attack, the muscles tighten around the airways and the lining of the airways
becomes inflamed and swollen, constricting the free flow of air. Because
children’s airways are narrower than those of adults, irritation that might
create minor problems for an adult may result in significant obstruction in the
airways of a young child. However, this disease affects all age groups: the
highest mortality rates from asthma occur among older adults.
A significant fraction
of the population may have airway hyperresponsiveness, an exaggerated tendency
of the large and small airways (bronchi and bronchioles, respectively) to
constrict in response to respiratory irritants, cold dry air, and other
stimuli. While airway hyperresponsiveness is considered a hallmark of asthma,
this tendency may also be found in many individuals without asthma as well; for
example, during and following a lower respiratory tract infection. In such
individuals, smoke exposure may cause asthma-like symptoms.
Individuals with COPD,
which is generally considered to encompass emphysema and chronic bronchitis,
may also experience worsening of their conditions because of
exposure to
wildfire smoke. Patients with COPD often have an asthmatic component to their
condition, which may result in their experiencing asthma-like symptoms.
However, because their lung capacity has typically been seriously compromised,
additional constriction of the airways in individuals with COPD may result in
symptoms requiring medical attention. Researchers have reported that
individuals with COPD run an increased risk of requiring emergency medical care
after exposure to particulate matter or forest fire smoke. Exposure to smoke
may also depress the lung’s ability to fight infection. People with COPD may
develop lower respiratory infections after exposure to wildfire smoke, which
may require urgent medical care as well. In addition, because COPD is usually
the result of many years of smoking, individuals with this condition may also
have heart disease, and are potentially at risk from both conditions.
Individuals with cardiovascular disease. Diseases of the circulatory system include
high blood pressure, cardiovascular diseases, such as coronary artery disease
and congestive heart failure, and cerebrovascular conditions, such as hardening
of the arteries (atherosclerosis) that bring blood to the brain. These chronic
conditions can render individuals susceptible to attacks of angina pectoris
(transient chest pain), heart attacks, sudden death due to a cardiac
arrhythmia, acute congestive heart failure, or stroke. Cardiovascular diseases
are the leading cause of mortality in the United States: about 30 to 40 percent
of all deaths each year. The vast majority of these deaths occur in people over
age 65. Studies have linked urban particulate matter to increased risks of
heart attacks, cardiac arrhythmias, and other adverse effects in those with
cardiovascular disease. People with chronic lung or heart disease may
experience one or more of the following symptoms: shortness of breath, chest
tightness, pain in the chest, neck, shoulder or arm, palpitations, or unusual
fatigue or lightheadedness. Chemical messengers released into the blood because
of particle-related lung inflammation may increase the risk of blood clot
formation, angina episodes, heart attacks, and strokes.
The elderly. Researchers have
estimated that tens of thousands of elderly people die prematurely each year
from exposure to particulate air pollution, as older adults are more likely to
have pre-existing lung and heart diseases, and therefore are more susceptible
to particle-associated effects. The elderly may also be more affected than
younger people because important respiratory defense mechanisms decline with
age. Particulate air pollution can compromise the function of cells involved in
immune defenses in the lungs, potentially increasing susceptibility to
bacterial or viral respiratory infections, which may carry a worse prognosis in
older adults.
Children. Children, even
those without any pre-existing illness or chronic conditions, are considered a
sensitive population because their lungs are still developing, making them more
susceptible to air pollution than healthy adults. Several factors lead to
increased exposure in children compared with adults: they tend to spend more
time outside; they engage in more vigorous activity; and they inhale more air
(and therefore more smoke constituents) per pound of body weight. These are all
reasons to try to limit children’s vigorous outdoor activities during smoky
conditions. Studies have shown that particle pollution is associated with
increased respiratory symptoms and decreased lung function in children,
including symptoms such as episodes of coughing and difficulty
breathing. These can
result in school absences and other limitations of normal childhood activities.
Pregnant women. While
there have not been studies of the effects of exposure to
wildfire smoke on
pregnancy outcomes, there is substantial evidence of adverse effects of
repeated exposures to cigarette smoke, including both active and passive
smoking.
Wildfire smoke
contains many of the same compounds as cigarette smoke. In addition, recent
data suggest that exposures to ambient air pollution in cities may result in
low birth weight, preterm birth, and possibly other more serious adverse
reproductive effects, including infant mortality. Therefore, it would be
prudent to consider pregnant women as a potentially susceptible population as
well.
Smokers. People who smoke,
especially those who have smoked for many years, have compromised lung
function. However, due to adaptation of their lungs to ongoing irritation,
smokers are generally less likely to report symptoms from exposure to irritant
chemicals than are nonsmokers. Nevertheless, they may still be injured by
wildfire smoke. Therefore, because they may not experience the same degree of
irritation from wildfire smoke as nonsmokers, some smokers may unwittingly put
themselves at greater risk of potentially harmful wildfire smoke exposures.
