Asthma inhalers emit significant greenhouse gases, may worsen climate impact: S'pore scientists

People living with asthma are most vulnerable when taking a breath of air, yet their use of widely prescribed inhalers to help them breathe better contributes to the worsening of air quality.

Doctors say asthma patients should be managing their conditions better instead of turning to the inhalers frequently for treatment, to prevent more damage to the environment.

Scientists from SingHealth Polyclinics (SHP) have found that these inhalers generate a significant amount of greenhouse gases.

"These are the L-shaped metered-dose inhalers that release small puffs to help ease breathing for patients with asthma. But they emit high levels of hydrofluorocarbon (HFC) propellants. The puffs add up," said Clinical Associate Professor Tan Ngiap Chuan, director of research at SingHealth Polyclinics.

"What this means is that when you use (the inhalers) and when the chemicals are released, they trap the heat within the environment, causing the temperature to rise."

HFC propellant is a type of aerosol propellant that uses a synthetic gas that contains hydrogen, fluorine, and carbon in products like hairsprays, deodorants and some inhalers.

Prof Tan and his team conducted two studies to understand the environmental impact of the metered-dose inhalers and assess the effect of the newer therapies in terms of asthma control and environment footprint.

On average, each patient using metered-dose inhalers with propellants in 2023 produced 140kg of CO2 emissions (CO2e) over a year, their studies found.

Based on the studies, The Straits Times calculated that inhalers used by one patient over a year emitted as much greenhouse gas as the average petrol-powered car that has travelled 97km, or from the eastern end of Singapore to the western end and back.

There is another kind of inhaler, a dry powder inhaler, for the treatment of asthma that produces less emissions. In 2023, the average individual patient using dry powder inhalers produced 121kg of CO2e, according to the SHP studies.

A dry powder inhaler depends on the user's "strong, deep inhalation" to suck the medicine into the airways, where it is then broken down for absorption, said Prof Tan.

"This has a significantly smaller carbon footprint and this lowering of environmental impact is a key reason why we recommend better control of the condition and switching (to this kind of inhaler)," he added.

Asthma is a chronic respiratory condition affecting millions worldwide. In Singapore, more than one in 10 people experience asthma at some point in his or her life, and one in 25 adults aged 18 to 69 currently lives with the condition.

"Singapore faces high rates of acute asthma care, with a hospitalisation rate that is three times higher that of the United States," said Prof Tan, who is also a senior consultant and family physician at SHP.

"The inhaled treatment is the best because it delivers the medication directly into the airway and the dose is tiny. These patients need to understand the use of such medication is treatment, and not when they get into trouble when they do not take care of themselves.

"Patients using the reliever inhaler for frequent asthma attacks are the ones who cause more damage to the environment," he added, referring to the studies' findings.

Besides inhalers, other asthma treatments include oral medications like oral corticosteroids for flare-ups and injections for severe asthma.

Also, patients can better manage their condition by paying attention to triggers of their allergies.

Prof Tan and his team looked at the difference between asthma patients whose condition was well controlled and those whose asthma was often triggered and whether turning to the inhaler as a solution would generate more carbon footprint.

The researchers analysed data from more than 23,000 adult patients with asthma who were receiving treatment from the nine polyclinics under the SingHealth cluster between 2015 and 2023.

They also looked at two different groups of patients - those using metered-dose inhalers and those using dry powder inhalers.

Their studies were published in July and August 2025 in Primary Care Respiratory Medicine under peer-reviewed journal Nature, which is the only scientific journal for the management of respiratory diseases in primary care.

The findings were similar to an earlier study by Dr Amanda Zain, a paediatrician in the Department of Paediatrics of Khoo Teck Puat - National University Children's Medical Institute at National University Hospital.

Her study, published in August 2024 in scientific publication Wiley, found that the propellants in asthma inhalers have a significantly disproportionate warming effect.

Inhaler use contributes 0.5 per cent of NUH's total greenhouse emissions, Dr Zain told ST.

"Inhalers can be life-saving medication in times of asthma attacks. But the use of at least three ventolin canisters a year constitutes ventolin overuse, so this is a medical issue much larger than the environmental impact," she said.

"Rather than to have patients worry about the environmental impact while dealing with their own acute physical well-being during an asthma attack, we should be asking, how (as healthcare professionals) we can better help control our patients' asthma so that they have fewer asthma attacks.

"This is better for patients and (incurs) less inhaler-related unnecessary carbon emissions," Dr Zain said.