You no doubt know at least one child who has a food allergy. Understanding why so many kids face this problem is something scientists have been studying and now they've identified another cause: second hand smoke.

A new Swedish study found children exposed to second-hand smoke face a greater risk for developing sensitivities to certain foods. The foods are what you'd predict: cow's milk, eggs, wheat, peanut, and fish.

It was a large study which enrolled more than 3,300 children. They were followed from birth to age 16. Researchers used questionnaires to track the kids' exposure to second hand smoke and their symptoms from food allergies.

The results show a clear relationship between second hand smoke and sensitivity to food starting at age 4. The effects persisted into adolescence. Food allergies can have a tremendous impact on children's lives. The healthcare costs to manage this long term health problem are significant.

Hundreds of chemicals in second hand smoke are toxic and at least 70 are carcinogens. In the US, it's estimated that 2.5 million nonsmokers have died from exposure to second hand smoke since the mid-1960s.

In children, there's strong evidence second hand smoke leads to more severe and frequent asthma attacks, and increases other respiratory and ear infections. During pregnancy, smoking can be deadly. It causes the deaths of one thousand babies each year.

So how can you protect children from the health effects of second hand smoke?

It's easy - don't smoke or allow others to smoke where you live or in your car, and choose a smoke free daycare. Though logical, people often find these decisions hard to make, especially when faced with family members who smoke. But now there's one more reason to say no.