Closing the doors and windows can reduce exposure to haze, but it does not make a home completely pollution-free. Indoor activities, ventilation and filtration all influence the air we breathe.
During a haze episode, people are commonly advised to remain indoors and keep their doors and windows closed. This is a useful first step, particularly when outdoor air quality is poor, but it does not guarantee clean indoor air.
Fine particles from outdoor haze can still enter a home, while activities such as smoking, cooking and burning incense or mosquito coils can generate additional pollution indoors. Protecting our health therefore requires attention to both outdoor haze and pollution produced inside the home.
What is PM2.5?
PM2.5 refers to airborne particles measuring 2.5 micrometres or less in diameter. A typical human hair is approximately 70 micrometres thick, making a particle at the upper end of the PM2.5 range about 30 times smaller than the width of a human hair.
Because these particles are so small, they can remain suspended in the air and penetrate deep into the lungs. Some of the smallest particles may enter the bloodstream, while those retained in the lungs can trigger inflammation that affects the respiratory and cardiovascular systems.
PM2.5 describes the size of the particles rather than their precise chemical composition. Nevertheless, exposure to elevated concentrations of fine particles is associated with significant health risks.
Can haze enter a closed home?
Yes. Closing doors and windows reduces the amount of outdoor air entering a home, but most homes are not airtight. Fine particles can travel with air through gaps around doors and windows, cracks, ventilation openings and other parts of the building.
The amount entering the home depends on several factors, including:
- the outdoor particle concentration;
- the condition and design of the building;
- how often doors and windows are opened;
- the type of ventilation or air-conditioning used; and
- whether effective particle filtration is available.
A modern building with a well-maintained air-handling and filtration system may offer greater protection than a naturally ventilated home. However, completely sealing a home indefinitely is not desirable either, as adequate ventilation is necessary to prevent the accumulation of carbon dioxide, moisture and pollutants produced indoors.
During severe haze, keep doors and windows closed as much as practicable. When outdoor conditions improve, ventilate the home to allow accumulated indoor pollutants to disperse.
Indoor air can sometimes be worse than outdoor air
Spending most of the day indoors does not necessarily eliminate exposure to PM2.5. Outdoor particles that enter a building may remain suspended indoors, while household activities can produce substantial amounts of additional particulate matter.
Common sources of indoor air pollution include:
- cigarette smoke and vaping aerosols;
- frying, grilling and other high-temperature cooking;
- mosquito coils;
- incense and candles;
- air fresheners and fragranced products;
- paints, solvents and cleaning products;
- emissions from new furniture and carpets;
- dust from renovation work; and
- hobbies and equipment such as 3D printers.
Exposure depends on both the concentration of a pollutant and the amount of time a person spends breathing it. Someone who remains for many hours in a poorly ventilated room containing an active pollution source may receive considerable exposure without going outdoors.
Does household air-conditioning remove PM2.5?
The split-unit air-conditioners commonly used in Malaysian homes mainly cool and recirculate indoor air. Their standard filters are generally designed to capture larger dust particles and protect the equipment, and not to remove PM2.5.
Air-conditioning may make it easier to keep windows closed, but it should not be assumed to provide fine-particle filtration. Filters should still be cleaned or replaced according to the manufacturer’s instructions so that the unit operates properly.
A portable air purifier fitted with a suitable high-efficiency particle filter (HEPA filter) can help reduce airborne particles when it is correctly sized for the room, operated for sufficient periods and properly maintained. Where volatile organic compounds, or VOCs, are a concern, a particle filter alone may not be sufficient; an appropriate gas-phase filter and careful control of the pollution source may also be required.
Everyday ways to reduce indoor pollution
The most effective approach is to prevent pollutants from being released indoors in the first place.
Smoking and vaping: Do not smoke or vape inside the home. Opening a window or moving to another room does not fully protect other household members. People who smoke should be encouraged and supported to stop.
Cooking: Use a kitchen hood or exhaust fan that vents contaminated air outdoors. Keep it clean and confirm that it is working effectively. During severe haze, avoid cooking methods that produce heavy smoke where possible.
Mosquito coils: Avoid burning coils indoors, particularly in closed rooms. Consider non-burning alternatives, while remembering that some electronic or chemical products can release VOCs and should be used according to their instructions.
Incense: Reduce the frequency and amount burned. If its use is important to religious or cultural practice, improve local exhaust ventilation or consider a non-burning alternative.
Paints, furniture and carpets: Choose lower-emission products where possible. Ventilate when outdoor air quality is better, or use filtration designed for the relevant pollutants.
Hobbies and 3D printing: Enclose the process where possible and use an effective exhaust system that releases contaminated air safely outdoors. Appropriate filtration may also be necessary.
Renovation work: Isolate the work area from occupied rooms and control dust at its source. Use local exhaust ventilation rather than allowing particles to spread throughout the home.
Three affordable actions for homes without an air purifier
Households do not necessarily need expensive equipment to make a meaningful difference. The three priorities are:
- Remove indoor pollution sources. Stop smoking and vaping indoors, avoid mosquito coils and incense, and reduce smoky cooking.
- Limit the entry of outdoor haze. When the Air Pollutant Index is elevated, keep doors and windows closed as much as practicable and minimise unnecessary opening of external doors.
- Create a cleaner room. Select one room, preferably away from the kitchen and other pollution sources, where vulnerable family members can spend time. Keep it clean, avoid activities that generate particles and maintain any air-conditioning equipment properly.
Ventilate the home when outdoor air quality improves. Avoid creating overcrowded conditions in a tightly closed room, especially for long periods.
Who is most vulnerable?
Short-term PM2.5 exposure can aggravate asthma and chronic respiratory disease and may increase the risk of cardiovascular events among susceptible individuals. Long-term exposure is associated with heart disease, stroke, chronic respiratory illness and lung cancer.
Those requiring particular protection include:
- babies and children, whose lungs are still developing and who breathe more air relative to their body size;
- older adults;
- pregnant women;
- people with asthma or other respiratory illnesses;
- people with heart disease; and
- individuals who work outdoors.
Outdoor workers, including food-delivery riders, traffic personnel, construction workers and others who must remain on the road, may experience prolonged exposure and should not be overlooked in public-health planning.
Symptoms that require attention
Poor air quality may cause:
- irritated or watery eyes;
- a scratchy or sore throat;
- coughing;
- wheezing;
- chest tightness;
- breathlessness;
- headache; and
- unusual tiredness.
These symptoms may have many possible causes, but vulnerable individuals should seek medical advice if they persist or worsen. Severe breathlessness, chest pain, confusion, bluish lips or difficulty speaking because of breathlessness requires urgent medical attention.
People with existing heart or lung conditions should continue taking their prescribed medication and consult their doctor about an appropriate haze-management plan.
The key question to ask at home
There is no single measure that guarantees completely “safe” indoor air. Risk depends on outdoor conditions, the building, activities inside the home, the health of its occupants and the effectiveness of any ventilation or filtration system.
The most useful question is:
What is polluting this room, and how can we reduce or remove it?
During haze, start by stopping anything producing smoke or fumes indoors. Keep outdoor haze out as far as practicable, protect vulnerable household members and make sure existing ventilation, exhaust and filtration measures are working properly.
Cleaner indoor air begins with controlling pollution at its source.
This public-education article was adapted from an interview with Prof Dr Victor Hoe which was published by The Star on 23 September 2026. Members of the public can monitor local air quality through Malaysia’s Department of Environment and follow current health advice from the Ministry of Health.
You must be logged in to post a comment.