Secondhand smoke and third-hand smoke -- the toxic residue left behind on walls, carpets, and clothes long after a cigarette is extinguished -- are bad news, especially for children, pregnant women, people with chronic illnesses, and the elderly, Winickoff and his colleagues note.

CNN: Should public housing projects go smoke-free?

They found that while 95% of non-smokers and 85% of smokers agreed that direct inhalation of second-hand smoke was harmful to children, just 65% of non-smokers, and 43% of smokers believed the same for "third-hand" smoke.

BBC: Warning over 'third-hand smoke'