Animals may end up needing pet medication if they inhale passive smoke, so owners should take them out of the room before lighting up.
Dr Pete Wedderburn, a vet writing for the Daily Telegraph, had a letter from a reader who said her daughter and step son smoke heavily and had four dogs, one of which recently died from carcinoma of the lung.
The reader wanted to know the link between passive smoke and cancer in dogs and Dr Wedderburn confirmed there is a connection between smoking and “increased concentrations of carcinogenic chemicals in tissue cells".
He wrote: “While there does not seem to be a categorically proven direct link between passive smoking and cancer in pets, this may be because enough research has not been done yet.
"If pet owning smokers refuse to give up, they should at least remove their pets from the room while they are lighting up."
He added that the link between cancer in pets and passive smoke is an area where more research is needed.