Second-hand smoke, also known as environmental tobacco smoke or ETS, is clearly associated with cancer, respiratory and cardiovascular disease in humans. Several studies have shown that up to 20 different carcinogens contained in tobacco smoke can be inhaled by non-smoking bystanders.
Dr. Timothy Fan, veterinary oncologist at the University of Illinois Veterinary Teaching Hospital in Urbana, explains that although associations between ETS and diseases in animals have not been as extensively researched, a handful of studies show a correlation between ETS and certain forms of cancer in pets.
A Tufts School of Veterinary Medicine study found a strong correlation between ETS and an oral cancer, squamous cell carcinoma, in cats. Cats living with smokers had higher incidence of this type of cancer. Cats living with more than one smoker and cats exposed to ETS for longer than five years have an even higher incidence of this cancer.
Why mouth cancer? Since cats groom themselves quite diligently, cats in smoking households can lick up carcinogens that have been deposited on their fur. Daily grooming over a long period of time can expose the delicate skin in the mouth to hazardous amounts of carcinogens.
The University of Massachusetts in Amherst also found that cats exposed to ETS have a slightly elevated risk of developing malignant lymphoma, or cancer of the lymph nodes. Since the lymph nodes filter the blood, inhaled or ingested carcinogens can build up in these structures.
In dogs, ETS is significantly associated with nasal sinus cancer and weakly associated with lung cancer. A study at Colorado State found a higher incidence of nasal cavity tumors in dogs exposed to ETS than in dogs that live in non-smoking households. This higher incidence was specifically found amongst long-nosed breed dogs such as Collies, and there was no significant increase in nasal tumors amongst short- to medium-nosed dogs exposed to ETS.
Dr. Fan explains that longer-nosed dogs may have a higher incidence of ETS-induced tumors for two reasons. "Smokers inhale smoke through their mouths, and it ends up depositing in the lungs. Bystanders, on the other hand, usually inhale ETS through the nose." Long-nosed dogs' nasal passages have a greater surface area on which carcinogens may be deposited before reaching the lungs.
"In addition," says Dr. Fan, "since a longer nose has nasal passages with a greater number of cells, there is a greater chance that one of these cells can be mutated by carcinogens into a cancer cell."
Colorado State also found that although short- to medium-nosed dogs exposed to ETS dont have a greater incidence of nasal tumors than those unexposed, they do have a slightly higher incidence of lung cancer, possibly because their shorter nasal passages are less effective at filtering carcinogens out of inhaled air before it reaches the lungs.
Unlike humans, who can develop bladder cancer as a result of ETS exposure, dogs and cats generally don't run a higher risk of bladder cancer when exposed.
As the human-animal bond becomes stronger, we share more of our lives, our leisure time and our living space with our companion animals, and they become exposed to the same environmental hazards that we do. Many of our habits, including smoking, can affect our pets as they would affect any other member of our household.
Designating a smoking area outside or in a physically separate room of the house may be on way to minimize ETS exposure for pets and other non-smoking family members.
- University of Illinois