A lot of parents cite having kids as one of the reasons why they've quit smoking. Indeed, how many studies have shown just how detrimental smoking is, not just to the health of the smoker, but also to all the other people around him/her breathing in secondary smoke? Here's another one: Swedish researchers say that exposure to secondhand smoke in early infancy can boost a child's risk of developing allergies.

Compared to children of nonsmokers, children exposed to secondhand smoke during early infancy were almost twice as likely to be allergic to inhaled allergens, such as pet dander, and about 50 percent more likely to have food allergies.

Interestingly, the study found no evidence that smoking during pregnancy affected a child's risk of becoming sensitized to certain allergens.