The risk is higher possibility of intaking excess alumnium, resulting in alumnium posioning--it is said to be one of the causes of Alzheimer's disease. However, the amount alumnium you ingest from foil in cooking should be extremely small. So don't worry too much about it. NOTICE: do avoid using aluminum foil in cooking tomatoes, fruitjoice, vinegar? etc. they contain acid and will react with the element: bad flavor and evil health damage.