A member asked:

How did we prove secondhand smoke was harmful?

A doctor has provided 1 answer

Observational study: We gain such data examining the frequency of health impairment in those exposed to 2nd hand smoke, compared to that of the unexposed. It is well documented that 2nd hand smoke increases crib death risk and doubles ear and bronchial infections in infants. These studies have been repeated many times with the same results.

Answered 3/24/2014

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