Hi Karin,   This was an interesting question. I know from many existing studies that secondhand smoke significantly impacts the onset of early asthma in children under the age of 4. And we also know that smoke can be a powerful asthma trigger in those already suffering from the disease. But I wasn't sure of the answer to your question about adult asthma risk, so I went on the hunt and found this article: http://ajrccm.atsjournals.org/cgi/content/abstract/172/1/61?etoc   The article, from an April 2005 issue of the American Journal of Respiratory and Critical Care Medicine, describes a research study done in Norway that looked at the effects of pre- or postnatal passive smoking on the adult incidence of asthma in 3,786 people  aged 15 to 70 years over an 11 year period.   What researchers found was that adult asthma risk was raised by as much as 17% by maternal smoking during childhood and slightly less when other members of the household smoked. Experts concluded that, "Exposure to pre- and postnatal smoking carries a substantial risk for developing adult asthma and respiratory symptoms."   Hope that answers your question...   To your health, Kathi