Asthma Triggers

An asthma attack can occur when someone with asthma is exposed to things in the environment, such as diesel exhaust, smog, house dust mites, and tobacco smoke. These are called asthma triggers. Asthma triggers cause symptoms in people who already have the underlying disease. One person’s triggers can be very different from those of another person with asthma. It is important to be aware of what your, or your child’s, triggers are.

Important asthma triggers you should be aware of:


Ozone is a common air pollutant created by the chemical interaction between nitrogen oxides (NOx) and volatile organic compounds (VOCs), in the presence of heat and sunlight. Ozone found at the ground level, also called smog, is unhealthy to breathe. (Ozone in the upper atmosphere, however, protects the earth from harmful UV radiation.) The chemical “ingredients” of ozone, NOx and VOCs, are combustion byproducts emitted by power plants, diesel engines, and cars. Hot and sunny days increase ozone levels.

Ozone triggers asthma attacks. People with asthma are more sensitive to ozone than other people and experience lung function changes and respiratory symptoms at lower concentrations or with greater magnitude than people without underlying lung disease. In addition, the injury, inflammation, and increased airway reactivity induced by ozone exposure may worsen a person’s underlying asthma. Source:

Quick facts:

  • Respiratory symptoms and bronchodilator use are increased when ozone concentrations are high
  • Lung function is reduced on days when ozone concentrations are high
  • The numbers of emergency room visits and hospital admissions for asthma are increased on days when ozone concentrations are high
  • Because the prevalence of asthma in children is higher than that of adults, and because children spend more time being active outdoors than adults, they are disproportionately affected by ozone exposure


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There is some evidence that ozone causes the development of asthma, but the research in this area is ongoing.

Diesel exhaust

Diesel exhaust is an example of a pollutant that both triggers asthma attacks and causes asthma.

Diesel exhaust is similar to tobacco smoke in the sense that it is a mixture of tiny particles and gases with many chemical components including nitrogen compounds, sulfur compounds, PAHs, benzene, carbon monoxide, and PM2.5. Collectively these components are known as diesel exhaust particles (DEPs). Diesel exhaust is emitted by trucks, school buses, trains, ships, harbor craft, off-road vehicles, and cargo-handling and industrial equipment with diesel engines.

When inhaled, DEPs can aggravate asthma and cause lung damage as well as premature death. The World Health Organization recently affirmed that DEPs cause lung cancer. See The EPA classifies diesel exhaust as a “likely” (but not definitive) carcinogen. Human epidemiological studies demonstrate an association between diesel exhaust exposure and increased lung cancer rates in occupational settings. Source:

Unfortunately, many diesel emission sources such as heavily traveled roads, ports, and rail yards are concentrated near densely populated areas, which leads to higher exposures and greater health consequences for our children.

Using proximity to traffic as a proxy for diesel exhaust exposure, researchers have found that exposure to traffic emissions is associated with increased risk of adverse respiratory health outcomes, including asthma incidence, severity, and persistence among children. Source:

Additionally, abundant evidence suggests that components of diesel exhaust can cause biologic responses that are related to asthma. Although evidence from research indicates that exposures to diesel exhaust and DEPs are associated with the inflammatory and immune responses involved in asthma, some questions remain regarding the underlying molecular mechanisms. Source:

In light of these findings, public health efforts to reduce exposures to diesel exhaust are warranted. In particular, reducing the exposure of infants and children should be a priority as part of a coordinated effort to improve the prevention and management of childhood asthma.

What Can I Do To Minimize My Risk? (From EPA)

  • Avoid idling if you have a diesel vehicle. This means turn off your engine when your vehicle is not in motion.
  • Keep your diesel vehicle well tuned and maintained.
  • If possible, retrofit diesel engines with pollution control devices.
  • If purchasing trucks or buses, consider buying those that meet EPA’s new standards ahead of schedule.
  • Get involved with your child’s school system. Many school buses run on diesel engines, but retrofitting such bus fleets to reduce diesel pollution is possible. For more information, see


Nitrogen dioxide (NO2) is a gaseous air pollutant composed of nitrogen and oxygen. An asthma trigger, NO2 forms when fossil fuels such as coal, oil, gas or diesel are burned at high temperatures.  NO2 also mixes in the outdoor air to form particle pollution and ozone. It is one of six widespread air pollutants that have National Ambient Air Quality Standards to limit them in the outdoor air. (The other five pollutants are Carbon Monoxide, Lead, Ozone, Particle Pollution, and Sulfur Dioxide or SO2.) NO2 forms quickly from emissions from cars, trucks and buses, power plants and off-road equipment. Source:

NO2 can also form indoors when fossil fuels like wood or natural gas are burned. This means that smoke from your stove or fireplace can trigger asthma.

In people with asthma, exposure to low levels of NO2 may cause increased bronchial reactivity and make young children more susceptible to respiratory infections. Long-term exposure to high levels of NO2 can lead to chronic bronchitis. According to the EPA, current scientific evidence links short-term NO2 exposures, ranging from 30 minutes to 24 hours, with adverse respiratory effects including airway inflammation in healthy people, increased respiratory symptoms in people with asthma and increased visits to emergency departments and hospital admissions for respiratory issues, especially asthma. Source:

Additionally, health studies have shown a connection between breathing elevated short-term NO2 concentrations, and increased visits to emergency departments and hospital admissions for respiratory issues, especially asthma. Source:

NO2exposure concentrations near roadways are of particular concern for susceptible individuals, including people with asthma, children, and the elderly.


Nitrogen oxides (NOx) refers to the sum of nitric oxide (NO) and nitrogen dioxide (NO2). NOx react with ammonia, moisture, and other compounds to form small particles. These small particles penetrate deeply into sensitive parts of the lungs and can trigger asthma attacks, cause or worsen respiratory disease, such as emphysema and bronchitis, and aggravate existing heart disease, leading to increased hospital admissions and premature death. Source:

According to the EPA, most airborne NOx comes from combustion-related emissions sources of human origin, primarily fossil fuel combustion in electrical utilities, high-temperature operations at other industrial sources, and operation of motor vehicles. However, natural sources, like biological decay processes and lightning, also contribute to airborne NOx. Fuel-burning appliances, like home heaters and gas stoves, produce substantial amounts of NOx in indoor settings. Source:

Ozone, or smog, is formed when NOx and volatile organic compounds react in the presence of heat and sunlight. Children, the elderly, people with lung diseases such as asthma, and people who work or exercise outside are at risk for adverse effects from ozone. These include reduction in lung function and increased respiratory symptoms as well as respiratory-related emergency department visits, hospital admissions, and possibly premature deaths. Source:


Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as “oxides of sulfur.”  The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%).  Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment. It is one of six widespread air pollutants that have National Ambient Air Quality Standards to limit them in the outdoor air. Source:

According to the EPA, current scientific evidence links short-term exposures to SO2, ranging from 5 minutes to 24 hours, with an array of adverse respiratory effects including bronchoconstriction and increased asthma symptoms.  These effects are particularly important for asthmatics at elevated ventilation rates (e.g., while exercising or playing.)  Source:

Studies also show a connection between short-term exposure and increased visits to emergency departments and hospital admissions for respiratory illnesses, particularly in at-risk populations including children, the elderly, and asthmatics. Source:

According to the American Lung Association, reducing SO2 levels are linked to an immediate gain in life expectancy, according to evidence from a study that examined the health impact of drops in sulfur dioxide. Source:


EPA’s National Ambient Air Quality Standard for SO2 is designed to protect against exposure to the entire group of sulfur oxides (SOx). SO2 is the component of greatest concern and is used as the indicator for the larger group of gaseous sulfur oxides (SOx).

Emissions that lead to high concentrations of SO2 generally also lead to the formation of other SOx. Control measures that reduce SO2 therefore can generally be expected to reduce people’s exposures to all gaseous SOx.

SOx can react with other compounds in the atmosphere to form small particles. These particles penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease, such as emphysema and bronchitis, and can aggravate existing heart disease, leading to increased hospital admissions and premature death.  EPA’s NAAQS for particulate matter (PM) are designed to provide protection against these health effects.


Particulate Matter

Particulate matter, also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets that can trigger asthma attacks. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

The size of particles is directly linked to their potential for causing health problems. The EPA is concerned about particles that are 10 micrometers in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs.

Particle pollution – especially fine particles – contains microscopic solids or liquid droplets that are so small that they can get deep into the lungs and cause serious health problems—including aggravated asthma and decreased lung function.

EPA groups particle pollution into two categories:

  • “Inhalable coarse particles,” such as those found near roadways and dusty industries, are larger than 2.5 micrometers and smaller than 10 micrometers in diameter.
  • “Fine particles,” such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.


Sources of PM emissions include: cars, trucks, power plants, fires, agriculture, dust, industrial processes. Click to view a summary of PM emissions in your state.

PM10 describes particles with a diameter of 10 micrometers or less (0.0004 inches or one-seventh the width of a human hair). PM10 includes fine particle pollution (PM2.5).

Sources of PM10 emissions include: motor vehicles, wood burning stoves and fireplaces, dust from construction, landfills, and agriculture, wildfires and brush/waste burning, industrial sources, and windblown dust from open lands.

When inhaled, PM10 particles evade the respiratory system’s natural defenses and lodge deep in the lungs. As the body reacts to these foreign particles, PM10 can increase the number and severity of asthma attacks, cause or aggravate bronchitis and other lung diseases, and reduce the body’s ability to fight infections.

Major concerns for human health from exposure to PM10 include: effects on breathing and respiratory systems, damage to lung tissue, cancer, and premature death. The elderly, children, and people with chronic lung disease, influenza, or asthma, are especially sensitive to the effects of particulate matter. Source:

PM2.5, commonly known as fine particle pollution, describes particulate matter that is 2.5 micrometers in diameter and smaller – 1/30th the diameter of a human hair.

Fine particle pollution can be emitted directly or formed secondarily in the atmosphere. There are different types of PM2.5. Sulfates are a type of secondary particle formed from sulfur dioxide emissions from power plants and industrial facilities. Nitrates, another type of fine particle, are formed from emissions of nitrogen oxides from power plants, automobiles, and other combustion sources.

Health studies have shown a significant association between exposure to fine particles and premature death from heart or lung disease. Fine particles can aggravate heart and lung diseases and have been linked to effects such as: cardiovascular symptoms; cardiac arrhythmias; heart attacks; respiratory symptoms; asthma attacks; and bronchitis. These effects can result in increased hospital admissions, emergency room visits, absences from school or work, and restricted activity days. Groups that may be particularly sensitive to fine particle exposure include people with heart or lung disease, older adults, and children. Source:


Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by the oil and gas industry, cars, trains, airplanes, ships, industrial processes, household wood fires, and incineration, as well as by plants and forests. They are also emitted by a wide array of household consumer products numbering in the thousands. Examples include: paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.

EPA studies found levels of about a dozen common organic pollutants to be 2 to 5 times higher inside homes than outside. While people are using products containing organic chemicals, they can expose themselves and others to very high pollutant levels, and elevated concentrations can persist in the air long after the activity is completed. Source:

Children who sleep in bedrooms containing fumes from water-based paints and solvents are two to four times more likely to suffer allergies or asthma, according to a study at Karlstad University in Sweden.


Polycyclic Aromatic Hydrocarbons (PAH) are a group of organic contaminants that form from the incomplete combustion of hydrocarbons, such as coal and gasoline. PAH often are byproducts of petroleum processing or combustion, and are highly carcinogenic at relatively low levels. Although they are relatively insoluble in water, their highly hazardous nature merits their positioning in potable waters and wastewaters. Additional sources of PAH include the burning of coal refuse banks, coke production, automobiles, commercial incinerators, and wood gasifers.

Members of this class of compounds have been identified as exhibiting toxic and hazardous properties, and for this reason the EPA has included 16 PAH on its list of priority pollutants to be monitored in water and wastes. Source:

In addition to anthropogenic sources, PAH are also formed from natural sources, including: forest fires, volcanic eruptions, and decomposition.

Exposure to PAH as a result of ambient air pollution has been associated with increased symptoms among asthmatics. Prenatal exposure to PAH from air pollution has also been linked to increases in cough and wheeze.


Many pesticides are sensitizers or irritants capable of directly damaging the bronchial mucosa, thus making the airway very sensitive to allergens or other stimuli. Pesticides may increase the risk of developing asthma, exacerbate a previous asthmatic condition or even trigger asthma attacks by increasing bronchial hyper-responsiveness. Source:

In addition to being proportionately more heavily exposed to pesticides than adults, infants and children are biologically more vulnerable to them.

Places where children may be exposed to pesticides:

  • Homes
  • Schools
  • Day-care centers
  • Parks and gardens

According to an article about pesticides and inner-city children, approximately 90% of American households use pesticides, and homeowners accounted for the purchase of an estimated 74 million pounds of the pesticides used in the United States in 1995, representing a nearly $2 billion industry. Diet, including drinking water, is a second important source of children’s pesticide exposure. Source:

Pesticide exposure can both cause and trigger asthma.

How do pesticides cause asthma? According to the advocacy organization Beyond Pesticides:

  • Numerous studies have found compelling evidence that exposure to pesticides is correlated with higher rates of asthma. One research focus has been on farmers and pesticide applicators (adults), groups typically exposed to higher levels of pesticides than the average population. Many studies have shown that this population has higher rates of asthma and other respiratory problems due to their use of pesticides. Yet occupational pesticide exposure is only one piece of the puzzle—household and community exposure to pesticides (where children are more prone) can also lead to respiratory problems. An early study done in the 1960s in Hawaii found that frequent household use of insecticides is correlated with an increased prevalence of respiratory disorders, including asthma and chronic bronchitis. The majority of the pesticides used were bug sprays for mosquitoes, flies, and cockroaches.
  • In children without previous respiratory problems, pesticides overwhelm the cells’ ability to detoxify chemicals, or cause immune and muscular effects, all of which can lead to respiratory problems.
  • Timing is crucial–The of over 4000 school-aged children studied in California, researchers discovered that children exposed to herbicides during their first year of life are four and a half times more likely to be diagnosed with asthma before the age of five; toddlers exposed to insecticides are more than twice as likely to get asthma.

How do pesticides trigger asthma? According to the advocacy organization Beyond Pesticides:

  • People with asthma are especially sensitive to pesticides and at risk of attacks when exposed to even small amounts. Most pesticides are small molecules that can exacerbate or aggravate asthma symptoms. Pesticides can trigger asthma attacks by increasing airway hyper-reactivity, which makes the airway very sensitive to any allergen or stimulus. Hypersensitive lungs are a trademark feature of asthmatics. Subsequent exposure to a stimulus can cause an extreme reaction in a hyper-reactive airway. In these situations, researchers at Johns Hopkins University believe that pesticides alter the nerve function controlling the smooth muscle lining of the airway, causing the airway to contract and restrain airflow, which is exactly what occurs during an asthma attack. Pesticides can also trigger asthma attacks by damaging lung epithelial cells directly.

While not all pesticides are associated with asthma, many are.

27 out of 30 commonly used lawn pesticides are sensitizers or irritants, and therefore have the potential to trigger asthma attacks, exacerbate asthma, or lead to a higher risk of developing asthma. Similarly, 39 of the 48 pesticides commonly used in schools are sensitizers or irritants. Many insecticides, herbicides and fungicides are linked to respiratory problems—click here for more info. Source:


High rates of childhood asthma are often attributed to exposure to cockroach allergens. Certain proteins are found in cockroach feces and saliva and can cause allergic reactions or trigger asthma symptoms in some individuals.

In a 2004 study, it was found that, among inner city children, cockroach exposure and sensitivity were predominate in the Northeast and cockroach allergen appears to have a greater effect on asthma morbidity than dust mite or pet allergen in these children.

While cockroaches pose a threat, you should not use toxic pesticides to kill the roaches—this may only make conditions worse for someone suffering from asthma.

Here are some tips from Beyond Pesticides for preventing cockroaches and asthma safely:

  • Remove all food waste and keep food in airtight containers.
  • Limit the spread of food around the house.
  • Eliminate potential water sources, such as leaky faucets and pipes.
  • Caulk and seal all cracks and crevices.
  • Vacuum frequently and intensively.
  • Monitor populations using sticky-traps.
  • In the event of infestation, use boric acid bait stations.

Disclaimer: this is meant to be used as a reference only, not a medical guide. Please consult your physician for any serious medical questions.

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