Haze is an atmospheric condition where particles, smoke, dust and moisture suspend in the air obscuring visibility.
Sources of haze include emissions from power plants, industrial activities, traffic as well as farming practices.
Forest fires in countries like the US, Australia and Europe during the hot and dry summer season are also a source of haze.
In Southeast Asia, haze poses a serious and recurring problem every year, particularly between May to October, due to the burning of forests in some countries to clear land.
How Haze Can Affect Your Health
In the 1997 Southeast Asian haze which affected a number of countries in the region, an increase in air pollutants from 50 to 150 μg/m3 is significantly associated with increases of 12% of upper respiratory tract illness, 19% asthma and 26% nasal inflammation (1).
Depending on how sensitive you are, the severity of the haze and the time of exposure, you may experience the following short-term adverse effects:
- Irritated eyes, watering eyes, and/or conjunctivitis (a type of eye inflammation);
- Running nose, stuffy nose, sneezing, and/or post-nasal drip;
- Throat irritation, dry throat, sore throat and/or coughing;
- Headache, dizziness and/or fatigue;
- Decreased lung function, depressed respiratory immune defenses, chest pain, and/or bronchitis (lung inflammation);
- Diarrhea and/or stomach upset, if drinking water sources are contaminated by dense haze and the water is consumed without further treatment;
- Anxiety, stress and/or depression-like symptoms such as insomnia, feelings of helplessness, loss of interest in daily activities and irritability.
These symptoms are usually mild and will subside when you stay indoor and limit your exposure to haze.
However, in susceptible individuals and those suffering from chronic disease, especially respiratory and heart disease (e.g. coronary artery disease, asthma and chronic obstructive pulmonary disease), their condition may be worsened by haze. They are more likely to experience more severe haze-related effects than healthy people.
As much as 94% of the particles in a haze are below 2.5 micrometers in diameter that is, particles that are 30 times smaller than the width of a human hair.
Due to their small size, these ultra-small particles stay in the air longer and are easily carried over long distances, increasing their chances of being inhaled by animals and humans.
Known as PM2.5 or fine particles, those particles emitted by forest fires are toxic to the lungs, and are more harmful than particulate matter collected from ambient air from the same region (2).
Fine particles can also bypass normal body defense mechanisms and penetrate deep into the lungs due to their minute size. When inhaled, they can enter the bloodstream and get absorbed by underlying tissue, potentially interacting with other compounds and substances in the body, such as LDL or ‘bad’ cholesterol, to produce damaging effects such as inflammation.
Below are some of the long-term risks associated with fine particles:
- In a large prospective cohort study of adults without pre-existing cardiovascular disease, individuals with higher exposure to fine particles (measured by PM2.5 readings) experience a faster rate of thickening of the arteries compared to others living within the same city (3). This implies that higher long-term PM2.5 exposures could promote the development of vascular disease.
- Long-term exposure to fine particles increases the risk of death by cardiovascular disease and reduces life expectancy by several months to a few years (4).
- Living in real-world levels of PM2.5 for 10 weeks promotes liver fibrosis, also known as liver scarring, and increases the risk of metabolic disease and liver dysfunction, as suggested by this animal study.
- Long-term exposure to PM2.5 pollutants may induce insulin resistance, inflammation and contribute to the development of diabetes (5, 6). A US epidemiologic study found that for every 10 μg/m3 increase of PM2.5, there could be a resulting increase of about 10,000 diagnosed cases of diabetes, or 1% increase in diabetes prevalence (7). Interestingly, an increase in diabetes risk exists even among areas that are below the US authority’s legal limits for PM2.5 (15 μg/m3). Populations living in areas that are near, but still below, the limits show a more than 20% higher diabetes prevalence compared with those in cleaner areas, an association that persisted after controlling for diabetes risk factors.
- A study comparing the respiratory health of common residents and traffic policemen, who are exposed to higher levels of PM2.5 due to their duties, found that the latter are more likely to suffer from respiratory symptoms and impaired pulmonary function (8). Other studies also linked increased chronic exposures to PM2.5 to population sinusitis in adults (9) and respiratory illness in infants (10).
- Exposure to polluted air by expecting mothers has also been associated with spontaneous abortion, under-weight infants, birth defects and infant death (11).
- A US study published in 2015 found that exposure to air pollution can make the brain age faster. Researchers found that for every 3.49 ug/cm3 increase in cumulative exposure to PM2.5, there is a 6.23 cm3 decrease in white matter. This is equivalent to about 1 ‐ 2 years of brain aging.