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The Haze You See Is Only Part of the Problem

August 13, 2026

A smoky skyline may be the most visible sign of haze, but it is not the part health experts watch most closely. The greater concern is what is floating in the air and how much of it you breathe.

For many people in Southeast Asia, haze has become familiar.

The skyline fades. The air smells burnt. Air-quality screenshots begin circulating in group chats, and anyone planning a run wonders whether to move it indoors.

If you can still see the buildings across the road and your throat feels fine, the situation may not seem particularly serious.

Health experts look at it differently.

They do not judge haze only by how the sky looks or whether symptoms appear immediately. Singapore’s National Environment Agency, or NEA, notes that neither visibility nor smell is a reliable measure of air quality. Humidity can obscure the view, while a burning smell does not always rise and fall in step with particulate pollution. 

The pollutant of greatest concern during haze is something far harder to see: fine particulate matter, commonly called PM2.5.

Why haze keeps returning

The haze affecting Singapore and neighbouring countries is often linked to smoke from forest and peatland fires in the region.

Dry weather, low rainfall and changing winds can allow the smoke to travel across national borders. Singapore is especially alert during the Southwest Monsoon season, when prevailing winds may carry smoke from fires elsewhere in the region towards the island. 

Not every dry season leads to a severe haze episode. Rainfall, wind direction, the number of active fires, and broader climate patterns all influence what ultimately reaches each country.

That uncertainty is why haze is monitored as a recurring regional risk rather than treated as a predictable annual event.

The particles that matter are too small to see

PM2.5 refers to particles measuring no more than 2.5 micrometres across.

Their small size allows them to travel deeper into the lungs than larger particles. Some may even pass into the bloodstream. This helps explain why fine-particle pollution is not viewed only as a cause of coughing or throat irritation. It may also affect the cardiovascular system. 

The amount of exposure matters too.

A short journey outdoors is different from spending hours exercising, commuting by bicycle or working in the open air. During strenuous activity, you breathe more deeply and rapidly, potentially drawing more polluted air into the lungs.

What this means for you: the skyline alone cannot tell you whether it is a good time for a long run. Official air-quality readings are more useful than appearance or smell.

What can haze do to your health?

Short-term exposure to high levels of haze particles may cause:

  • Irritated or watery eyes
  • A dry or sore throat
  • Coughing or nasal irritation
  • Wheezing or breathlessness
  • Worsening asthma or other existing respiratory symptoms

For many healthy people, mild irritation improves once exposure falls. Symptoms can be more serious for someone with asthma, chronic obstructive pulmonary disease, heart failure or another long-term heart or lung condition.

The effects are not always immediate. NEA notes that symptoms may sometimes appear one to three days after exposure.

Local research also shows why respiratory health receives particular attention during haze episodes. A Singapore study examining nearly 5.8 million emergency-department visits found that every 30-point rise in the Pollutant Standards Index, or PSI, was associated with a 2.3% increase in respiratory emergency visits and a 2.7% increase in respiratory hospital admissions. It did not find a significant rise in total visits or admissions across all conditions.

This was an observational study, so it shows an association rather than proving that haze caused every additional case. Even so, it provides useful local evidence that poorer air quality can place added pressure on respiratory health services.

What about the long-term risks?

This is where careful wording matters.

Large international studies have linked continuous, long-term exposure to fine-particle pollution with heart disease, stroke, chronic respiratory illness, respiratory infections and lung cancer. The World Health Organization considers ambient air pollution a major environmental health risk.

Singapore’s haze pattern, however, is usually intermittent. Exposure may last several days and vary considerably from one year to another.

NEA states that there is limited robust evidence on the long-term effects of this particular pattern of short, episodic haze exposure. Most long-term studies involve people exposed to elevated air pollution continuously over several years. 

So a few hazy days do not mean that someone will inevitably develop a chronic illness.

The immediate concern is clearer: high particulate levels can irritate healthy people, worsen existing heart or lung conditions and contribute to respiratory problems. The broader research on long-term PM2.5 exposure helps explain why health authorities take fine particles seriously and seek to reduce unnecessary exposure.

Who needs to be more careful?

Anyone may experience symptoms when pollution levels rise, but some people are more susceptible:

  • Children
  • Older adults
  • Pregnant women
  • People with chronic heart or lung conditions
  • People who work or exercise outdoors for extended periods

A healthy adult may tolerate a short outdoor journey without difficulty. Someone with asthma may experience symptoms much sooner.

Risk depends on several factors working together: the pollution level, time spent outside, intensity of activity and the person’s underlying health. 

Should you check the PSI or PM2.5 reading?

In Singapore, the 24-hour PSI and 1-hour PM2.5 concentration serve different purposes.

The 24-hour PSI reflects average air quality over a longer period. It is useful for planning the next day, for prolonged outdoor work, or for activities that may last several hours.

The 1-hour PM2.5 reading gives a more immediate picture of current conditions. Check it now when deciding whether to go for a walk, run, or outdoor workout.

Readings can fluctuate as weather and wind conditions change, so a morning check may not reflect the air quality later in the day. 

What should you do when the air worsens?

The aim is not to eliminate every trace of exposure. That is rarely possible. The practical goal is to reduce unnecessary exposure.

Adjust outdoor activity

When the 24-hour PSI reaches the unhealthy range, healthy people should reduce prolonged or strenuous outdoor exertion. Vulnerable groups are advised to take additional precautions in line with the official health advisory. 

Moving a hard workout indoors, shortening an outdoor session or choosing a gentler activity may be enough.

Keep indoor air cleaner.

When outdoor conditions worsen:

  • Close doors and windows
  • Avoid smoking, candles and other sources of indoor particles
  • Use wet wiping or mopping instead of dry dusting
  • Reopen the home when outdoor air improves

A portable air purifier may further reduce indoor particle levels. NEA recommends highly efficient filters such as HEPA filters and choosing a purifier suited to the room’s size. For haze, the unit’s smoke Clean Air Delivery Rate is the most relevant rating. 

Understand when an N95 mask may help.

An N95 respirator can filter fine particles when it fits the face properly, but it is not necessary for every brief trip outdoors.

NEA advises that healthy people generally do not need one for short exposures such as commuting. A person who must remain outdoors for several hours during hazardous air quality conditions may benefit from wearing a well-fitting N95 mask. 

N95 masks also make breathing more difficult. Older adults, pregnant women and people with serious heart or lung conditions should speak with a doctor if they are unsure whether wearing one is suitable.

When the air is very unhealthy, reducing time outdoors is usually more important than relying on a mask to continue as normal.

Keep medication accessible

People with asthma or other chronic heart and lung conditions should continue their prescribed treatment and keep necessary medication nearby.

Seek medical care if you experience:

  • Significant difficulty breathing
  • Severe or worsening wheezing
  • Chest pain
  • Symptoms that continue after exposure has been reduced

The bottom line

The most noticeable part of haze is not always the most important.

A grey skyline may prompt concern, but the real health question is how much fine particulate matter is in the air, how long you are exposed and whether your health makes you more vulnerable.

Check the official readings. Adjust prolonged outdoor activity when needed. Keep indoor air as clean as reasonably possible, and pay attention to symptoms.

Because when it comes to haze, what you cannot see may matter more than what you can.

Sources

Editorial Note

This article is intended for general information and should not replace personalised medical advice. The effects of haze vary with pollutant levels, exposure duration, activity level, and individual health. Speak with a qualified healthcare professional if you are concerned about breathing symptoms, an existing heart or lung condition, or whether an N95 respirator is suitable for you. Seek prompt medical attention for chest pain, significant breathlessness or severe or worsening symptoms.

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