Really? And what studies would that be?  My father suffers from COPD and never smoked but out of 50 plus years of marriage my mother smoked 30 of those years.  Doctors emphatically recognize my father's COPD is from second hand smoke.  Also the athletically induced asthma both my sister and I have suffered from since high school is from growing up breathing second hand smoke.  All the research I have ever read clearly supports the dangers of second hand smoke and my own family respiratory issues prove it as well.