Additives Chemical substances are often mixed with food to ease their processing and storage or increase their appetizing. In manufactured foods Food additives are only permitted in quantities well tolerated proved in laboratory tests. It is often complicated to outweigh the benefits of additives (eg. As reduced waste, increased food diversity, or protection against food poisoning) against the associated risks. For example prevented. As nitrite, which is used for cured meat, the growth of Clostridium botulinum and improves the flavor. However, nitrite converts to nitrosamines, which proved in animal studies to be carcinogenic. On the other hand, the amount of nitrite, which is applied to cured meat, small compared to the amount of nitrate which is naturally present in foods and is converted by the salivary glands in nitrite. Vitamin C can prevent the formation of nitrite in the gastrointestinal tract. In rare cases, additives such as sulfite solve from a food allergy. Most of these reactions caused by the use of common foods. Arrears Sometimes limited amounts of residues in food allowed because they can not be completely removed without damaging the food. Among the common residues include pesticides, heavy metals such as lead, cadmium or mercury, nitrates in leafy green vegetables, aflatoxins in nuts and milk, growth-promoting hormones in dairy products and meat, also animal hair and feces and body parts of insects. By the US Food and Drug Administration (FDA) limits were estimated at a level in which they did not cause any diseases or adverse effects in individuals. but it is difficult to prove a causal relationship between extremely low values ??and harmful effects in the long run possible, but are unlikely. Reliable values ??are often determined in accordance with generally accepted views as based gapless evidence.