Wood Smoke, Indoor Air, and Asthma

February 16, 2012

In many parts of the country-and for people of all ages-a turn of the calendar to the winter months means more time spent indoors. For patients with asthma, however, an evening spent in front of a crackling fire may simply serve as a trigger for an attack.

In many parts of the country-and for people of all ages-a turn of the calendar to the winter months means more time spent indoors. For patients with asthma, however, an evening spent in front of a crackling fire may simply serve as a trigger for an attack.

The results of several recent studies show that, like oil and water, smoke and asthma don’t mix very well. A team of Canadian researchers examined the association between three measures of smoke exposure, physician visits, and hospitalizations occurring in 281,711 persons over a 92-day period.1 Not surprisingly, the number of respiratory and asthma-specific physician visits and hospitalizations among study participants increased directly with the extent of exposure to particulate matter. Rappold and colleagues,2 working out of the US Environmental Protection Agency (EPA), found a similar association between inhalation of peat fire smoke and asthma episodes as well as respiratory hospitalizations among a group of North Carolina residents. Unlike the Canadian researchers, Rappold found that cardiovascular events also increased with exposure to smoke.

The combination of gas and particulate matter released into the air when wood burns is so harmful for respiratory health that the EPA offers a program called Burnwise: Learn Before You Burn (www.epa.gov/burnwise). For example, the EPA advises that you: 

  • Only burn dry wood that has been split, stacked, covered, and stored for at least 6 months.

  • Have stoves and chimneys inspected every year by a certified professional to remove any creosote buildup and to confirm the absence of gaps, cracks, or unwanted drafts in the chimney.

  • Periodically replace old wood stoves with new, more efficient heating appliances.

In addition, all heaters must be vented to the outside to prevent buildup of carbon monoxide. Carbon monoxide detectors should be available and functional in homes equipped with heating appliances.

Smoke is not the only threat for patients with asthma, of course. The EPA notes that indoor air can be up to 100 times more polluted than outdoor air. Sobush and Burrescia,3 writing about indoor air quality, list a plethora of other respiratory assailants:

  • Biological contaminants: Bacteria, molds, mildew, viruses, animal dander, dust mites, cockroaches, pollen, rodent excrement.

  • Chemicals and chemical solutions: Pesticides, carpet-cleaning residues and adhesives, formaldehyde, aerosol sprays, office equipment chemicals (especially those from photocopiers and computers), paint-stripping chemicals.

  • Ion depletion or imbalance in the air: Excess of positive over negative ions.

  • Particulates: Asbestos.

  • Ionizing radiation: Radon.

In an extensive review of the literature, Jie and colleagues4 found a direct connection between poor indoor air quality and asthma morbidity. The worst asthma triggers were fuel combustion, mold growth, and environmental tobacco smoke.

Tools are available to help ensure that indoor air quality is not worsening a patient’s chances of having an asthma attack. The World Health Organization, for instance, offers air quality guidelines to reduce the adverse health effects of pollution, outlined in the Table below.5

PollutantExposure Averaging TimeAQG Value
Particulate Matter (PM1 year

24 hours10 μg/m

Particulate Matter (PM1 year

24 hours20 μg/m

Ozone (O8 hours, daily maximum100 μg/m
Nitrogen Dioxide (NO1 year

40 μg/m3

Source: World Health Organization Air Quality Guidelines for Exposure to Reduce Adverse Health Effects of Pollution.5

Several Internet sites are a ready source of information about air quality. The Web site AIRNow, http://www.airnow.gov/index.cfm?action=aqibasics.aqi explains the Air Quality Index (AQI) and how it relates to health for persons with and without conditions that predispose them to respiratory attacks as a consequence of exposure to pollutants. The site offers a list of helpful publications, a link to an AQI calculator, and an EnviroFlash newsletter for those interested in receiving air quality alerts. State of the Air, http://www.stateoftheair.org, from the American Lung Association, allows site visitors to check the state of their air by geographic location.

Patients who suffer from asthma are often well practiced at avoiding their triggers. But reminders always bear repeating. So a quick conversation during an office visit about indoor air quality during the winter months and how to prevent or minimize exposure to irritants is a good way to keep the physician-patient dialogue open.



1. Henderson SB, Brauer M, Macnab YC, Kennedy SM. Three measures of forest fire smoke exposure and their associations with respiratory and cardiovascular health outcomes in a population-based cohort. Environ Health Perspect. 2011;119:1266-1271.

2. Rappold AG, Stone SL, Cascio WE, et al. Peat bog wildfire smoke exposure in rural North Carolina is associated with cardiopulmonary emergency department visits assessed through syndromic surveillance. Environ Health Perspect. 2011;119:1415-1420.

3. Sobush D, Burrescia M. Perspective paper: assessing air quality as part of a physical therapy plan of care. Cardiopulm Phys Ther J. 2011;22:20-24.

4. Jie Y, Ismail NH, Jie X, Isa ZM. Do indoor environments influence asthma and asthma-related symptoms among adults in homes? A review of the literature. J Formos Med Assoc. 2011;110:555-563.

5. World Health Organization. WHO Air Quality Guidelines for Particulate Matter, Ozone, Nitrogen Dioxide and Sulfur Dioxide: Global Update 2005 Summary of Risk Assessment. Geneva: World Health Organization; 2006.