There are different levels of severity of smoke injury. Acute injury results from smoke inhalation when an animal is trapped in a house or brush fire, or otherwise inhales large amounts of smoke over a short period. Secondly, chronic injury resulting from low-grade exposure to smoke can occur, as in situations where the pet lives with heavy smokers (termed side-stream or second hand exposure) or they are exposed to indoor combustion sources (coal or kerosene heaters). The response of the pet to smoke is very similar to the responses humans have to this toxic mix.

Smoke Inhalation

Exposure to a large intake of smoke results in increased breathing efforts due to swelling in the upper airway, and faster and deeper breaths to try and increase the uptake of oxygen across the injured lung lining cells. The bronchi tend to spasm, and the irritation results in production of a lot of mucus, leading to cough. Sometimes tissue fluid also builds up in the lungs. Damaging components include the heat itself, the irritating particles, and carbon monoxide inhalation. Once the initial damage occurs, the abnormal lung environment is often colonized by bacteria, leading to secondary bronchitis or pneumonia. If damage is extensive, airways may be permanently dilated, there may be scarring, and there may be a chronic cough due to difficulty clearing the mucus. Sometimes the little hairs that act as elevators to clear secretions, (called cilia) are stripped away and this can lead to permanent accumulation of secretions in the lower airways.

Second Hand Low-grade Smoke Inhalation

Cigarette smoke has many carcinogenic compounds (e.g., nitrosamines and polycyclic aromatic hydrocarbons) and these can settle in the airways, and be absorbed particularly easily through the delicate membranes in the alveoli (breathing sacs). Chronic exposure to smoke has been proven to increase the incidence of lung and throat cancer in humans. A weak relationship between dogs living with a smoker, and increased risk of lung cancer was found in a case control study almost 10 years ago. A recent case control study did find that household exposure to coal or kerosene heaters increased risk for sinonasal cancer in dogs. Sinonasal refers cancer of the nose/sinus cavities. Another case control study a few years ago established that if exposure to cigarette smoke over time is equal between dogs, long nosed dogs (dolichocephalic) like collies are at a higher risk for nasal cancer.

It is wise to minimize the exposure of dogs and cats to smoke, both direct exposure and indirect exposure.