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.