Should you buy an air purifier? Here’s what top pulmonologists in Delhi say

According to Dr G C Khilnani, chairman of Pulmonary, Critical Care and Sleep Medicine at PSRI Hospital, there is no scientific evidence or study which can prove the health benefits of an air purifier. One should not assume that an air purifier kept in one’s living room can clean the air of the entire house.

How should one use an air purifier?

Dr Khilnani says air purifiers have two components – a filter which stops PM 2.5 and PM 10 particles and an adsorbent which adsorbs pollutant gases like NO2, carbon monoxide, etc. An air purifier should have both. It should be of good quality and should be commensurate with the volume of the room.

Air purifiers should be kept on all the time and not just when you enter the room because otherwise the utility is reduced. The direction of the air should be towards the area where you sit or sleep. The room should be kept closed all the time because if you keep opening windows and doors, its efficacy is reduced.

“As a pulmonologist and a person who has been working on air pollution for years, I am also a member of an expert committee on global air pollution’s effects on health. This issue has been discussed in Geneva meetings as well. People who are suffering from asthma, Chronic Obstructive Pulmonary Disease (COPD), heart disease, bronchitis, or immunosuppression, and can afford to stay within closed doors should use air purifiers, particularly in the National Capital Region (NCR) when the AQI is severe,” he adds.

But poor maintenance can lead to harmful effects. Unless the filter is changed periodically, it could imbibe fungi which can cause serious infections.

Will an air purifier be able to tackle the kind of pollution in Delhi?

Not really, says Khilnani. “If you keep an air purifier in the living room and think that it is purifying the air, it is incorrect. It has to be a closed room. When the AQI is 400-500 or on Diwali, perhaps it can reduce the PM 2.5 to 150 after it is run the whole night. They are not 100 per cent efficacious but somebody who is unwell and has breathing difficulties may benefit by using it in the correct way.”

Air purifiers can be especially beneficial during times of high outdoor pollution or for people with respiratory issues, allergies, or asthma. However, it has side effects as well.

How can an air purifier help?

According to Dr Nikhil Modi, senior consultant, Respiratory and Critical Care, Indraprastha Apollo Hospitals, air purifiers with high-efficiency particulate air (HEPA) filters can capture up to 99.97 per cent of particles as small as 0.3 microns. They can reduce the presence of allergens and irritants that trigger respiratory symptoms.

Models with activated carbon filters are also effective in removing odours and VOCs (volatile organic compounds) from cooking, cleaning products, and smoke. Regular use can lead to fewer allergy and asthma symptoms as many airborne triggers are effectively removed. Cleaner air, especially free of allergens, can improve sleep, as respiratory discomfort can disrupt sleep cycles.

What are the potential side effects of air purifiers?

Dr Modi says some air purifiers (especially those with ionizers) emit trace amounts of ozone, which can irritate the lungs and worsen asthma or allergy symptoms. It is recommended to choose models certified by standards like California Air Resources Board (CARB) for safe ozone levels. Extended use can cause dryness in the air, which may dry out skin and mucous membranes, especially during winter.

A humidifier can help balance this if it becomes an issue. Some models can be noisy, especially at higher fan speeds, which might be bothersome at night. Checking for noise levels before purchase can help avoid disruptions. Frequent filter replacements can be costly, but not replacing filters can reduce effectiveness and potentially harbour allergens.

How often must the filter be replaced when the pollution levels are as high as seen in Delhi?

According to Dr Modi, air purifiers can significantly improve indoor air quality in high-pollution environments like Delhi, where AQI often dips to hazardous levels. However, extreme pollution places a heavy load on filters, especially during periods when particulate matter (PM2.5 and PM10) levels are extremely high. In these conditions, a HEPA filter’s lifespan may reduce drastically—potentially needing replacement every 1-3 months instead of the usual 6-12 months.

For optimal performance, regular maintenance and possibly an additional pre-filter layer to capture larger particles are recommended. The high pollution levels may also require air purifiers to run at higher fan speeds, which can further accelerate wear and filter saturation. Regular filter checks are essential, as clogged filters lose effectiveness and may even become sources of trapped pollutants re-circulating into the air if not replaced promptly.

Will keeping indoor plants serve as an alternative?

Dr Vikas Mittal, pulmonologist at the CK Birla Hospital, says indoor plants like peace lilies, snake plants, and spider plants can help absorb some pollutants and improve air quality modestly, especially in terms of CO2 and some volatile organic compounds. Indoor plants supplement air purification efforts but should not replace air purifiers entirely.

However, studies have shown that their effect is relatively limited in comparison to air purifiers, particularly for particulate matter like PM2.5, which is prevalent in polluted cities. Plants need to be in high numbers and placed strategically throughout a home to have any measurable effect, and even then, they don’t eliminate the smallest harmful particles.