Bushfires and asthma

Bushfires (also known as known as wildfires, forest fires and wildland fires) have become one of the biggest environmental threats to human health along with climate change (Johnston et al. 2012, Xu et al. 2020). In Australia, fire has always been integral to the landscape. Large vegetated areas of the continent burn every year, and episodic severe bushfire disasters have been documented since European colonisation. In the context of climate change, more extreme and highly polluting fires are becoming more common and the duration of fire seasons is lengthening. The escalation in severe bushfires was illustrated by the Australian ‘Black Summer’ of 2019-20 (Cowie et al. 2021, Xu et al. 2020).  During this period, more than 10 million Australians were exposed to bushfire smoke for periods ranging from weeks to months (Johnston et al. 2021, Walter et al. 2020).

Bushfire smoke is made up of a mixture of particulate matter (PM), and a range of gases such as carbon monoxide, nitrogen dioxide and volatile organic compounds (Reid et al. 2016), which have adverse impacts on human health. A study reported that bushfire-related fine particulate matter (PM_2.5) can be more detrimental to human health than other sources of PM_2.5 (Aguilera et al. 2021) although there is still much research being undertaken to determine the relative toxicity of different sources of PM_2.5. Moreover, toxicological studies have indicated that bushfire-related PM is more toxic to the lungs than equal doses of PM from other sources (Kim et al. 2018, Wegesser et al. 2009). 

Pregnant women and their offspring, and people with asthma, are particularly vulnerable to the health risks associated with bushfire smoke exposure (Vardoulakis et al. 2020). Pregnant women with asthma may be even more vulnerable to the effects of bushfire smoke due to physiological changes during pregnancy such as increased oxygen consumption and an increase in the amount of blood pumped by the heart.

The association between bushfire smoke exposure and asthma-related outcomes in non-pregnant people has been reported in multiple studies (Borchers Arriagada et al. 2019, Bui et al. 2021, Gan et al. 2020). A study of the impact of 2019/2020 bushfires in people with asthma has shown that people with asthma were more likely to report respiratory symptoms and healthcare service utilisation including hospitalisation, emergency department visits and use of medications during the bushfire period compared to people without asthma (Bui et al. 2021); however, no published study has looked specifically at the effects in pregnant women with asthma.  

There is strong evidence in the general population demonstrating that exposure to bushfire smoke increases the risk of poor pregnancy outcomes (Abdo et al. 2019, Amjad et al. 2021, Heft-Neal et al. 2022). Exposure to bushfire smoke has been shown to increase the risk of adverse health outcomes for the mother (Abdo et al. 2019) including:  

• Stress and depression (Beyene et al. 2022)
• Diabetes during pregnancy (Abdo et al. 2019)
• Increased blood pressure during pregnancy (Abdo et al. 2019)
• Miscarriage (Xue et al. 2021)
• Respiratory and non-respiratory symptoms (Willis et al. 2020)

Exposure to bushfire smoke during pregnancy has also been shown to increase the risk of adverse health outcomes for the fetus/newborn (Abdo et al. 2019, Heft-Neal et al. 2022, Park et al. 2022, Requia et al. 2022) including:

• Preterm birth (Abdo et al. 2019, Heft-Neal et al. 2022, Requia et al. 2022)
• Low birth weight (Abdo et al. 2019)
• Child death in low and middle income countries (Li et al. 2022, Xue et al. 2021)

View Infographic: Impact of bushfire smoke on pregnancy outcomes, here.

• Ensure asthma is well controlled

If smoke is a known trigger for people with asthma, it is recommended that they use a preventer during bushfire season or if they live near an area where hazard reduction burns are planned. Reinforce medication adherence in patients, and check inhaler technique.

•  Stay indoors

The effectiveness of staying indoors depends on how well the house/building seals to reduce smoke from coming indoors. Advise people with asthma to close all windows and doors in their homes, seal large gaps as much as possible, and if available, use a HEPA filter and an air-conditioner that re-circulates inside air. This will reduce the amount of particles entering the building from the outdoors. If doors and windows are open, the amount of particulate matter indoors and outdoors might be the same. Foam tape and draft strips (available from hardware stores) can be used to seal around doorframes and windows to prevent smoke seeping in. Wet towels can also be used to block drafts under doors and bigger gaps around windows. No building can keep outdoor air pollution out completely, so people should open the doors and windows again once the outdoor air quality has improved.

Staying indoors can be unrealistic when severe smoke pollution persists over long periods.  Keeping the windows closed can result in higher levels of indoor humidity, PM_2.5, carbon dioxide (CO₂) and overheating due to a lack of air circulation (ventilation) (Vardoulakis et al. 2020, Reisen et al. 2019). During prolonged and localized bushfire periods, it is recommended that people with asthma relocate to a different area that has better air quality where possible. People with asthma who do not have air conditioning at home could also be encouraged to visit other buildings with air conditioning and good air filtration, such as libraries and shopping centres or other homes.

People with asthma living in bushfire risk areas should be encouraged to have a ‘Fire Emergency plan’ and be prepared by having a sufficient supply of essential items like food and medicines, including asthma puffers and/or oral corticosteroid tablets on hand to last for a number of days to minimise the need to go outdoors. Foods that have a long shelf life or can be stored in the freezer are recommended, to reduce the need to leave the house for groceries. For example, bread can be frozen to extend its shelf life, ultra-heat treatment milk can be purchased and stored in the fridge when opened. Fruits and vegetables provide good nutrition and many are shelf/fridge stable. Wholegrain crispbreads, crackers and nuts and nut spreads can also be stored in the pantry. Alternatively, if available home delivery could be used.

• Minimise or avoid additional sources of indoor air pollution

Other sources of indoor air pollution include candles, wood fires, vacuums without a filter, incense sticks, and cigarette smoke. These sources can increase the levels of potentially harmful substances such as particulate matter (PM), carbon monoxide, polycyclic aromatic hydrocarbons and nitrogen oxides.

• Air conditioning or air purifiers

There is good evidence to show that High-Efficiency Particulate Absorbing (HEPA) filters reduce exposure to poor quality and improve health (Jia-Ying et al. 2018, Vardoulakis et al. 2020). If available, people with asthma should use an air purifier with HEPA filter that is appropriately sized for the intended room, in a room that is well sealed. The filters should be cleaned regularly and must be replaced every 12 to 18 months. Household air conditioners are not made to filter out particles, but they may still help in improving air quality. It is recommended people with asthma only use air conditioners that circulate indoor air, where outdoor air quality is poor.

• Avoid exercising outdoors

During bushfire smoke events, outdoor activity should be avoided to minimise exposure (Vardoulakis et al. 2020).  People with asthma should avoid outdoor exercise or strenuous physical activity when outdoor air quality is poor. During exercise, people can increase their air intake 10 to 20 times over their resting level and as a result more pollutants may enter deep into the lungs. Minimising physical activity reduces the amount of inhaled air pollutants and lessens adverse health risks during a bushfire smoke event.

Encourage people with asthma to check air quality in their local area before exercising outdoors. If outdoor air quality is poor, alternative options include exercising indoors in air conditioned gyms, which are likely to have better air quality, or at-home, with online exercise classes for example.

• Use a P2/N95 facemask

It has been reported that face masks (P2/N95) are effective in guarding against bushfire smoke exposure (Kodros et al. 2021). A case study of the 2012 Washington state wildfire season in the US, showed the use of P2/N95 facemasks decreased respiratory hospitalisations attributable to bushfire smoke by 22% – 39% (Kodros et al. 2021).

Face masks might be appropriate for those who cannot avoid being outdoors during periods of poor air quality. However, they must be fitted well and maintain a tight seal to be effective. Wearing a face mask may make breathing more difficult and result in discomfort. If people with asthma have difficulty breathing or are facing other symptoms whilst wearing a facemask, they should remove it, and seek a place with cleaner air.

P2 masks should be removed and disposed of when they become moist or after about four hours of continuous use since the seal will not be as effective.

View NSW Health guide on how to place P2/N95 face masks correctly.

• Recirculate air inside vehicles

Put air conditioners in recirculate mode and close windows and vents when inside a vehicle during bushfire periods to avoid drawing smoky air into the car.

• Follow local air quality data

Evidence suggests that real-time air quality data can provide useful information on air pollution to assist people to plan their daily activities. Therefore, people with asthma should check local air quality information and public health messages. Australian state health departments and environmental protection agencies provide up-to-date information on air quality data (See Websites- Air quality, below). This information can be used to make informed decisions to reduce peoples’ exposure to bushfire smoke, such as minimising/rescheduling outdoor activities or seeking alternative low air pollution areas. People can also follow their local mass media for air quality reports.

• Use digital technology

In Australia the following Apps and websites can be used to observe air quality/bushfires:

• Bushfire smoke and your health: translated information about health and wellbeing via Health Translation
• NSW Health Bushfire response and recovery page – advice and fact sheets
• Aust. Dept Health & Aged Care – Bushfire Smoke – Vulnerable groups fact sheet
• Air Pollution and Pregnancy information leaflet – from the The Royal Australian & New Zealand College of Obstetricians and Gynaecologists