Traffic Pollution: Asthma Trigger?

Traffic-related air pollution is a major cause of childhood asthma. It is estimated that up to 38% of all annual childhood asthma cases in Bradford, UK, may be caused by air pollution. A study found that children exposed to high levels of traffic-related air pollution have a higher risk of developing asthma.

Air pollution can make asthma symptoms worse and trigger asthma attacks. The estimated six million children in the United States with asthma are especially vulnerable to air pollution.

The causal relationship between air pollution and asthma remains controversial, but a large number of studies have provided evidence of the involvement of air pollutants in asthma onset and exacerbations.

Traffic-related air pollution

TRAP is a complex mixture of PM derived from combustion and non-combustion sources, such as road dust, tyre wear, and brake wear. It also includes primary gaseous emissions, such as NOx. TRAP is a significant risk factor for asthma development in children.

TRAP can induce asthma symptoms, exacerbations, and decreases in lung function. It can also increase the risk of sensitisation and the responses to inhaled allergens in individuals with asthma.

TRAP exposure is associated with an increased risk of asthma exacerbations, subsequent emergency room visits, and hospital admissions in children. It is also associated with poorer asthma control, a higher proportion of severe asthma, and worsening of lung function in exposed individuals.

TRAP exposure is associated with more symptoms of asthma, a higher rate of exacerbations, and a negative impact on lung function.

Nitrogen dioxide

NO2 can also form indoors when fuels like wood or gas are burned. It is one of six widespread air pollutants for which there are national air quality standards to limit their levels in the outdoor air.

Scientific evidence suggests that exposure to NO2 could likely cause asthma in children. A 2022 review of multiple studies found that elevated levels of NO2, as well as elevated particulate matter and sulfur dioxide, were strongly associated with heart and lung harm, affected pregnancy and birth outcomes, and were likely associated with increased risk of kidney and neurological harm, autoimmune disorders, and cancer.

NO2 causes a range of harmful effects on the lungs, including:

• Increased inflammation of the airways
• Worsened cough and wheezing
• Reduced lung function
• Increased asthma attacks
• Greater likelihood of emergency department and hospital admissions

People who live near the emission sources of NO2 are at higher risk. Other vulnerable subpopulations at higher risk from nitrogen dioxide exposure include:

• Individuals who are pregnant
• Infants, children, and teens
• Older adults (>65 years of age)
• People with pre-existing medical conditions such as asthma, chronic obstructive pulmonary disease (COPD), cardiovascular disease, diabetes, lung cancer
• Current or former smokers
• People with low socioeconomic status

Second-hand smoking

Second-hand smoke is a mixture of gases and fine particles that includes smoke from burning tobacco products, such as cigarettes, cigars, or pipes, and smoke that has been exhaled by someone who smokes. It contains more than 7,000 chemicals, including hundreds that are toxic and about 70 that can cause cancer.

Second-hand smoke is a common trigger for people with asthma, especially children and babies. Breathing just a small amount of second-hand smoke that contains thousands of chemicals can cause a severe asthma attack.

Second-hand smoke exposure leads to more than 880,000 deaths annually, according to the World Health Organization. Exposure to second-hand smoke for 1 hour has been shown to reduce lung function for the following hour, and prolonged second-hand smoke exposure has been shown to increase wheezing and other respiratory symptoms, and perhaps the susceptibility to asthma and chronic obstructive pulmonary disease (COPD).

Passive smoking has been extensively studied in children, and it has been found that maternal smoking during pregnancy and childhood reduces lung function, and increases the risks of asthma and wheezing in offspring. It has been suggested that the lungs are vulnerable during pregestation and childhood, and that second-hand smoke exposure during these stages may be particularly damaging to the lungs. Studies have also suggested that second-hand smoke exposure in adult life leads to reduced lung function, and maybe increased risk of asthma and COPD, as well as respiratory symptoms such as breathlessness and coughing.

Outdoor air pollution

Traffic-related air pollution (TRAP) is a complex mixture of particulate matter derived from combustion and non-combustion sources, and primary gaseous emissions including nitrogen oxides. TRAP can cause oxidative injury to the airways, leading to inflammation, remodelling, and increased risk of sensitisation.

Children are particularly vulnerable to the adverse effects of air pollution due to their developing lungs, immature metabolic pathways, high ventilation rates per bodyweight, and increased time exercising outdoors.

The impact of outdoor air pollution on asthma could be modified by other individual factors like obesity, as reported in most studies. A large cross-sectional study found that the effect of NO2 and SO2 on asthma was significantly greater in overweight or obese children. Similarly, the exposure to O3 is associated with a poorer lung function for obese adults when compared to people with a normal weight.

Global measures that aim to reduce exposure to air pollutants are highly needed in order to improve the outcomes and management of adult and paediatric asthma in addition to the existing guidelines.

Indoor air pollution

Indoor air pollutants include products of combustion, such as particulate matter (PM) and oxides of nitrogen (NOx), as well as airborne allergens and endotoxins. These pollutants can cause a range of health issues, from minor symptoms like sneezing and coughing to more severe outcomes such as cancer and the exacerbation of chronic respiratory conditions like asthma. The impact of indoor air pollution on asthma is particularly notable in children, who are more susceptible to the effects of these pollutants.

Several studies have found a strong relationship between indoor fine PM exposure and exercise-induced respiratory symptoms in children with asthma. The deposition of coarse PM in the upper airways can lead to bronchial hyperreactivity, triggering asthma symptoms. Additionally, indoor exposure to NO2 and secondhand smoke (SHS) is associated with a higher risk of asthma exacerbations, increased respiratory symptoms, and poorer lung function. The negative effects of indoor air pollution on asthma are more pronounced in individuals with double exposure to both indoor and outdoor pollutants.

To manage asthma and reduce the impact of indoor air pollution, preventive measures are essential. This includes smoking cessation, improving household ventilation, using clean fuels (e.g., methane, liquid petroleum gas, electricity), and employing portable air cleaners. Following asthma management guidelines can help minimize exposure to indoor pollutants and improve asthma outcomes. It is crucial to address indoor air pollution through global measures to protect vulnerable individuals and improve respiratory health for people with asthma.

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