First, when you use hot coals to cook protein foods such as meat, pork, chicken or fish, mutagens get formed as the food is charred. Then, during cooking, as fat drippings hit the hot coals, the potent carcinogen benzopyrene is formed. It rises in the smoke and is carried back to the food. Mutagens are so named because they have the ability to cause mutations, or changes, in a cell's genetic material. The danger is not so much that a mutation does occur, it's what the result of the changes might be.
Some mutations are harmless, but others can lead to cancer and birth defects.
A carcinogen such as benzopyrene, on the other hand, is a substance that has been shown to cause cancer. This tells us what CAN occur without saying anything about the chances that it actually will. To answer this we need to know about barbecue's relative risk. Now this isn't the danger that your in-laws will drop by, it is a convenient way of viewing one hazard in relation to others. Traveling 300 miles by car.