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Are the effects of second hand cigarette smoke as harmful to cats and dogs as it is to humans? I have never seen this discussed anywhere.

            This is a variation of one of the most commonly asked questions by pet owners once they are given a diagnosis of cancer in their family pet – how did this happen? Unfortunately, this is a very complicated question and there is rarely a single cause of cancer. Although it is very difficult to establish a clear cause and effect between something like second hand smoke and cancer in pets, the evidence for environmental factors being involved is mounting in veterinary medicine.

            One study revealed only a slight increase in the development of lung cancer in dogs living with a smoker and this risk did not increase with greater second hand smoke exposure. There is actually more evidence linking second hand smoke with other types of cancers in pets. Cats living in a household with a smoker have been shown to have an increased risk of developing both lymphoma and cancer of the mouth (squamous cell carcinoma). Regarding lymphoma, the risk became even greater with increased time and amount of exposure to the smoke. It is suspected that cats are at greater risk of problems from second hand smoke because the smoke settles on their fur which is then ingested during their fastidious grooming habits. This results in ingestion of the carcinogens with high concentrations in the oral cavity.

            Along with these findings in cats, there is concern over environmental factors being linked to cancer in dogs. There is some evidence of a potential increased risk of bladder cancer in dogs that have been exposed to certain types of herbicides and pesticides. There is also a reported increased incidence of lymphoma, cancer of the tonsils, and cancer of the nasal passages in dogs that live in urban areas as opposed to rural settings.

            Despite all of these reports of possible environmental causes of cancer in pets, there have been no definitively proven links. Cancer takes time to develop; often extended periods of exposure to a carcinogen are needed in order for the damage to be done that can ultimately result in cancer. This means that pets may be less affected by these situations compared to humans who can potentially have decades of exposure to second hand smoke and other dangerous substances. However, it does make sense for pet owners to take any precautions possible to try to limit their four-legged family members’ exposure to potential carcinogens. This preventative strategy combined with regular examinations by your veterinarian is the best way to try to ensure your pets stay healthy.  

Stephen Brenn, DVM, DACVIM (Oncology)

Dr. Brenn received his DVM degree from the College of Veterinary Medicine at North Carolina State University. He then completed an internship at the New Haven Central Hospital for Veterinary Medicine and remained in Connecticut to live and practice general medicine. He recently completed a three year residency in oncology at the Animal Medical Center in New York City. Dr. Brenn enjoys music, sports, and spending time with his two sons.