Passive smoking can seriously damage the health of pets like dogs and cats. Smoke irritates their respiratory systems and carries toxic and carcinogenic substances that pets ingest. Certain dogs that have flat faces have an increased risk of lung cancer if they live with a smoker. Studies have shown passive smoking can cause cancer of the nasal passages in cats and dogs. Tobacco companies also fund experiments on animals to study tobacco, but these have not provided useful insights into how smoking causes cancer in humans. Cigarette butts are a visible form of pollution that ends up in oceans and beaches, and can be ingested by animals, posing health risks. People are encouraged to quit smoking to protect their own health and that of their pets and wildlife.