FAQ: Impact of Haze on Health

1. What are the main air pollutants emitted into the environment?

The main air pollutants are sulphur dioxide, oxides of nitrogen, carbon monoxide, organic compounds and particulates. Photochemical reactions involving oxides of nitrogen and organic compounds upon emission produce ozone which is also a key air pollutant in the environment.

2. What are the key air pollutants of concern during the haze period?

The key air pollutant of concern during the haze period is particulate matter (PM). Short term exposure (i.e. continuous exposure to unhealthy daily average PSI levels over a period of a few days) to these air pollutants can cause respiratory symptoms and aggravate existing heart or lung disease. Exposure to particulate matter may also cause irritation of the eyes, nose and throat in healthy individuals.

3. What are the effects of haze on my health?

Short-term effects of haze:

Among healthy individuals, short term exposure (i.e. continuous exposure to unhealthy daily average PSI levels over a period of a few days) to high levels of haze particles may cause irritation of the eyes, nose, and throat in healthy individuals. Such irritation resolves on its own in most cases.

Haze particles can affect the heart and lungs, especially in people who already have chronic heart or lung disease e.g. asthma, chronic obstructive pulmonary disease (COPD), or heart failure.

There may be up to 1-3 days of time between exposure to haze and health effects/symptoms.

Long-term effects of haze:

Singapore is not affected by the haze throughout the year. Any exposure is short-term in nature (i.e. continuous exposure to unhealthy daily average PSI levels over a period of a few days) and such exposure may vary from year to year. As international studies are based on long-term exposure to air pollution, there is little robust data on the longer-term effects of short-term exposure to haze like the pattern seen in Singapore.

Studies have shown that persons living overseas with continuous exposure over several years to high ambient pollution from fine particles (i.e. particulate matter 2.5 (PM 2.5); particles smaller than 2.5 micrometers), may have a higher risk of;

cardiovascular effects, such as heart attacks,

reduced lung development, as well as

the development of chronic respiratory diseases, such as asthma, in children.

4. Since Singapore experiences short-term exposure to haze, what local studies have been conducted to assess and quantify the short-term effects?

MOH has conducted studies to assess the short-term effects of air pollution on the health of the general population, using air quality data from 1994-2012. One study found that an increase of 10g/m3 daily concentration of PM10 and PM2.5 was associated with a 1.1% increase in hospital admissions for respiratory diseases. Another study on the health effects of previous haze episodes (1994, 1997, 2006 and 2010) showed that a 10-unit increase in 24-hr PSI was associated with 3.1% increase in hospital admissions for asthma. The estimates obtained from the local studies were within the range of estimates from international studies.

5. Although Singapore is not affected by haze throughout the year, it may keep recurring. Will we then be studying the long-term effects of short-term exposure to haze?

There is currently no data both locally or internationally, that looks into the long term health impact of short-term, episodic exposure to haze.

Researching this would be highly challenging. Any results would be based on observational studies only, which would not be able to show a definite cause-and-effect relationship. It would be difficult to study the direct long-term health effects due to the episodic exposure to haze, as there could be many other contributing factors to the long-term health outcome we are measuring. For example, it would be difficult to be sure that intermittent exposure to haze twenty years ago caused the chronic obstructive pulmonary disease (COPD) in a person today, since COPD could also have been caused by other factors such as smoking, previous lung infection, or existing lung diseases.

Although there are overseas studies of long-term health impact, these have been based on long-term exposures, which are different from the pattern of exposure here. These studies showed that continuous, long-term exposure to air pollutants over several years may result in lung function abnormalities in children and subsequently, in adulthood. This could lead to greater susceptibility to the effects of ageing, infection and other pollutants, such as tobacco smoke, in adults.

6. How is the air quality forecasted? Why is the health advisory based on 24-hour PSI forecast?

During haze episodes, NEA will provide an air quality forecast for the next 24 hours. NEA will look at all relevant factors, including weather conditions, in determining this forward projection.

Health impacts are related to concentrations as well as duration of exposure, in addition to the health status and level of activity of the individual. The health advisory issued in the daily haze situation update is based on 24-hour PSI forecast as scientific and epidemiological studies on the health effects of particulate matter have been based on 24-hour PSI.

For more information on MOH haze health advisory, please refer to Annex A.

7. Which groups of people are more sensitive to haze?

In general, children, elderly, and people with chronic lung disease, heart disease are more sensitive to the health effects of haze, and should adopt the preventive measures in the MOH health advisory when air quality is poor. Individuals are advised to consult their doctor should they develop breathing difficulties. In addition, it is advised that pregnant women reduce exposure to haze for the health of their unborn baby.

8. What is MOH's advice to the public?

The public is recommended to adhere to the MOH haze health advisory (Annex A). In most cases, it is still safe to carry on with outdoor activities. However, drinking plenty of water may help symptoms such as a dry or itchy throat.

Individuals with existing chronic heart and lung conditions should ensure that your medications are on hand and readily available.

Each individual's reaction to pollutants may vary, and the amount of physical activity or exertion that can be performed differs according to your health status or physical capacity. Should you encounter symptoms or discomfort, please take additional measures to prevent further exposure.

Although the general advice to the public when the forecasted air quality is good or moderate (PSI?100) is to maintain normal activities, vulnerable persons, especially those with chronic heart and lung conditions who develop symptoms or feel unwell, should seek medical attention promptly.



The health impact of haze is dependent on one's health status (e.g. whether one has pre-existing chronic heart or lung disease), the PSI level, and the duration and intensity of outdoor activity. Reducing outdoor activities and physical exertion can help limit the ill effects from haze exposure. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention.

Source: Ministry of Health, Singapore