Little holes in your aluminum foil can occur and develop during the cooking process due to acids eating away at the aluminum foil.
It's normal and also common to see those little holes when you use foil to cover foods that are high in acid, particularly tomatoes or tomato sauces.
It can leave dark spots on lasagne as well as holes in the foil. Other things can cause the reaction, too, particularly salt and citrus fruit.
Reynold's says a reaction happens when aluminum foil comes in contact with salt, vinegar, highly acidic foods -- such as tomatoes -- or highly spiced foods.
The aluminum foil seems to dissolve or get eaten away, but what happens is it turns into an aluminum salt.
While it is true that some aluminum gets into food when cooked in aluminum foil or with aluminum cookware, and that this is enhanced in acidic foods, it is not true this causes any health effects in healthy adults.
Most people think it matters whether aluminum foil is used shiny side up or down, but the surprising truth is that it doesn't make a difference.
The variation is a result of the manufacturing process—the shiny side comes in contact with highly polished steel rollers, and the matte side doesn't.
At home, people use aluminum foil for food storage, to cover baking surfaces and to wrap foods, such as meats, to prevent them from losing moisture while cooking.
People may also use aluminum foil to wrap and protect more delicate foods, like vegetables, when grilling them.