Cooking is a complex process involving several different types of reaction including oxidation, pyrolysis and the Maillard reaction which is associated with browning. Cooking also leads to phase-changes, where solids become liquids and liquids become gases. Phase-changes differ from reactions in that they are reversible e.g. if animal fat turns from the solid phase to the liquid phase due to an increase in temperature, it will revert back to the solid phase when it cools down.
The type of fumes released during cooking also depends on what is being cooked, with fats, proteins and carbohydrates emitting different chemical compounds. Especially unpleasant fumes, including polycyclic aromatic hydrocarbons (PAHs) and carbon monoxide, are emitted when fats and oils undergo pyrolysis, which requires temperatures higher than those normally used for cooking. However, these conditions can occur when fat drips onto a barbeque for example, and also during the cleaning cycle of a pyrolytic self-cleaning oven, where the oven temperature may be raised to 500°C.