People unwilling to quit smoking to improve their own health may consider giving up cigarettes to spare their pets the harmful effects of second-hand smoke, U.S. researchers said on Monday.

Twenty-eight percent of pet owners who smoke said in a survey they would try to quit based on knowledge that second-hand smoke could harm their dogs, cats and other pets, the researchers wrote in the journal Tobacco Control.

Another 11 percent said they would think about quitting.

"It's not necessarily that people love their pets more than they love themselves or their children, it's just another motivational factor for people to consider quitting smoking," Sharon Milberger of the Henry Ford Health System in Detroit, who led the research, said in a telephone interview.

Milberger said asking smokers to quit for the sake of their pets may be an appealing new way to get them to throw away their cigarettes. Of the 71 million pet owners in the United States, about a fifth are smokers, Milberger estimated.

Just under 20 percent of Americans smoke, according to the U.S. Centers for Disease Control and Prevention.

Just as second-hand smoke can harm people, studies indicate it can raise a pet's risk of lung cancer and other forms of cancer, allergies, eye and skin diseases and respiratory problems, the researchers said.

The findings were based on a Web-based survey of 3,293 U.S. pet owners, mostly from Michigan.

Among the nonsmokers who owned pets and lived with someone who did smoke, 16 percent said they would ask that person to quit and 24 percent said they would tell the smoker to light up outside instead of indoors, the study found.

"It would be hard to believe that there's any smoker out there now who doesn't know that smoking is bad for them and the people around them," Milberger said.

"For tobacco control advocates, on our team we can now have vets and kennels and pet supply stores. So, for example, when someone takes Fluffy in to the vet, the vet can ask them about their smoking behavior and whether they allow smoking in their home," added Milberger, a nonsmoker with a 1-year-old cat.