One of the best parts of summer, in my opinion, is barbecue. See that marshmallow? It's perfect. Brown all the way around, gooey all the way to the center. You know it will melt in your mouth. I didn't take the photo. That's because my marshmallows inevitably burst into flame and end as cinders with cold, white centers. I imagine either type of toasted marshmallow contributes to your cancer risk. So does anything charred, like seared steak or hamburgers from the grill or even burnt toast.

The carcinogen (cancer-causing agent) is mainly benzo[a]pyrene, though other polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs) are present and can cause cancer, too. PAHs are in smoke from incomplete combustion, so if you can taste smoke on your food, expect it contains those chemicals. Most of the PAHs are associated with smoke or char, so you can scrape them off your food and reduce your risk from them (though that kind of defeats the point of a toasted marshmallow). HCAs, on the other hand, are produced by a chemical reaction between meat and high or prolonged heat. You'll find these chemicals in fried meat as well as barbecue. You can't cut or scrape away this class of carcinogens, but you can limit the amount that is produced by cooking your meat just until it's done, not blackening it into oblivion.

Just how dangerous are these chemicals? The truth is, it's very hard to quantify the risk. There is no established "this amount will cause cancer" limit because the genetic damage that leads to cancer is complex and affected by many other factors. For example, if you drink alcohol with your char, you further increase your risk, since alcohol, though it doesn't cause cancer, acts as a promoter. This means it increases the likelihood a carcinogen will be able to induce cancer. Similarly, other foods may lessen your risk. What is known is that PAH's and HCA's definitively cause cancer in humans, but they are also a part of everyday life, so your body has mechanisms for detoxifying them. What you want to do is try to limit your exposure. I guess that means you should take the time to toast the perfect marshmallow rather than go for the quick sugary fireball, but that's just so hard... You can also try to eat your greens to help cure cancer and learn about the most poisonous chemicals.