Fresh meat can be cooked for immediate consumption, or be processed, that is, treated for longer-term preservation and later consumption, possibly after further preparation. Fresh meat cuts or processed cuts may produce iridescence, commonly thought to be due to spoilage but actually caused by structural coloration and diffraction of the light. A common additive to processed meats for both preservation and the prevention of discoloration is sodium nitrite. This substance is a source of health concerns because it may form carcinogenic nitrosamines when heated.