Wood burning smoke is a source of particulate pollution both indoors and outdoors. Wood burning smoke can worsen asthma and exacerbate allergic conditions. It is not usually a threat to people without asthma, allergies or other respiratory conditions.

Wood burning smoke can come from wood stoves, fireplaces, forest fires or agricultural fires. Wood stoves and fireplaces are the primary source of wood smoke pollution indoors, though large smoky forest fires can affect indoor areas in some regions. Forest and agricultural fires are the primary source of wood smoke pollution outdoors.

Wood smoke is made up of a complex mixture of gases (carbon monoxide, nitrogen dioxide and carbon dioxide, among others) and fine particles produced when wood and other organic matter burns. The health threat from smoke comes from these gases and fine particles. The microscopic particles can get into the eyes and respiratory system. Wood smoke exposure can depress immune system activity and cause damage to the cells that protect and cleanse the airways.

The seasonality of exposure to wood burning smoke varies with the source. Wood stoves and fireplaces are used inside and tend to be used during colder months. Forest and agricultural fires tend to occur in the spring and summer months.

The health effects of wood smoke can lead to the worsening of allergy and asthma symptoms. Wood stoves and tobacco smoke are the primary indoor pollutants linked to the development and aggravation of respiratory conditions. In addition to the particles released, combustion always produces water vapor. Water vapor can result in high humidity and wet surfaces. These conditions encourage the growth of other indoor allergens such as dust mites and molds.

Wood smoke can make it more difficult for people to breathe deeply or vigorously, and create coughing, wheezing, chest tightness, irritated sinuses, stinging eyes, runny nose and shortness of breath.

People with respiratory conditions are not the only population affected by wood burning smoke. Children may be more susceptible to smoke because their respiratory systems are still developing. Children breathe more air per pound of body weight than adults, and tend to be more active indoors and outdoors. Research has shown that children who grow up in wood burning households have a significantly higher chance of developing asthma. The elderly and people with preexisting heart conditions are also more susceptible.