Secondhand smoke is not only harmful to humans, it may also cause cancer in household pets such as dogs, cats and birds, Oklahoma State University researchers said last week.

"There have been a number of scientific papers recently that have reported the significant health threat secondhand smoke poses to pets," said Dr. Carolynn MacAllister, an Oklahoma State University Cooperative Extension Service veterinarian, in a news release. "Secondhand smoke has been associated with oral cancer and lymphoma in cats, lung and nasal cancer in dogs, as well as lung cancer in birds."

Veterinarians from Oklahoma State, including McAllister, authored a paper on the harmfulness of tobacco smoke to pets based on research conducted in 1992 and 1998, and a more recent study conducted by Colorado State University.

MacAllister said that secondhand smoke has been linked to an increased occurrence of cancer in the nose and sinus area among dogs, as well as a "slight" association with lung cancer. She said the Colorado State study shows that there is a higher incidence of nasal tumors in dogs living in a home with secondhand smoke compared to dogs living in a smoke free environment.

Shorter or medium nosed dogs showed higher rates for lung cancer. Cats living with smokers are also twice as likely to develop malignant lymphoma, a cancer that occurs in the lymph nodes and that is fatal to three out of four cats within 12 months of developing it.