Exogenous chemicals exist in the external environment of human life, and may contact with the body and enter the body, showing certain biological effects in the body. They are also called "exogenous bioactive substances". It includes not only substances used by human beings in food production and processing, but also substances existing in the growth process of food itself. Pesticide residues on vegetables are harmful, but some exogenous chemicals are beneficial to health, such as allicin in garlic. Exogenous chemicals should not be considered harmful to health. With the rapid development of economic globalization, trade liberalization and international food trade, the importance of food safety is becoming more and more prominent. While the world food trade greatly enriches people's diet and improves their quality of life, there are more and more food safety problems caused by food additives, microorganisms, heavy metals, agricultural and veterinary drugs, epidemics, etc., and food safety has attracted more and more attention and attention. This paper discusses the sources of foreign chemicals in food and drinking water and their harm to human health through some cases. Known poisons are defined as chemicals that cause injury or death after contact with human body. So what? At present, the word "exogenous chemicals" has been used instead of poison. What do foreign chemicals mean? Metabolic pathways that do not occur in organisms? But through external channels into the organism? And has no inherent biological function. The choice of this word means its double meaning? Regardless of contact conditions? No foreign chemical substance is "safe"? When limiting its exposure dose and exposure conditions? No foreign chemical substance is "unsafe" when used. There is no absolute boundary between poison and non-poison? Some foreign chemicals may be harmful under certain conditions? Under other conditions, it may be non-toxic. Like what? Under normal circumstances, fluorine is an essential trace element in human body composition? But what about the excessive fluoride absorbed by the human body? Can be used on bones? The exchange of hydroxyl and bicarbonate ions with bone salt crystals indicates that hydroxyl and bicarbonate ions of hydroxyapatite lime have been exchanged? And form insoluble calcium fluoride by inhibiting phosphorylase or combining with calcium ions in body fluids? So that the body's calcium and phosphorus metabolism is disordered? It leads to a series of pathological changes such as hypocalcemia, dental fluorosis and skeletal fluorosis. And what if fluorine and its compounds come into direct contact with respiratory tract and skin? It will produce strong irritation and corrosion. What does this mean? Distinguish whether a chemical substance is toxic or nontoxic. The dose and route of exposure must be fully considered. Known poisons of exogenous chemicals are defined as chemicals that cause injury or death after exposure. So what? At present, the word "exogenous chemicals" has been used instead of poison. What do foreign chemicals mean? Metabolic pathways that do not occur in organisms? But through external channels into the organism? And has no inherent biological function. The choice of this word means its double meaning? Regardless of contact conditions? No foreign chemical substance is "safe"? When limiting its exposure dose and exposure conditions? No foreign chemical substance is "unsafe" when used. There is no absolute boundary between poison and non-poison? Some foreign chemicals may be harmful under certain conditions? Under other conditions, it may be non-toxic. Like what? Under normal circumstances, fluorine is an essential trace element in human body composition? But what about the excessive fluoride absorbed by the human body? Can be used on bones? The exchange of hydroxyl and bicarbonate ions with bone salt crystals indicates that hydroxyl and bicarbonate ions of hydroxyapatite lime have been exchanged? And form insoluble calcium fluoride by inhibiting phosphorylase or combining with calcium ions in body fluids? So that the body's calcium and phosphorus metabolism is disordered? It leads to a series of pathological changes such as hypocalcemia, dental fluorosis and skeletal fluorosis. And what if fluorine and its compounds come into direct contact with respiratory tract and skin? It will produce strong irritation and corrosion. What does this mean? Distinguish whether a chemical substance is toxic or nontoxic. The dose and route of exposure must be fully considered. 2. Toxicity refers to the exposure of exogenous chemicals to the body or after entering the susceptible parts of the human body? Relative ability to cause damage. The more harmful foreign chemicals are to the body? The more toxic it is. Highly toxic substance? Only a relatively small dose or concentration will cause certain harm to the body? And less toxic substances? Higher doses or concentrations are needed to show toxic effects. Absorption of exogenous chemicals The process of exogenous chemicals entering the blood through various biomembranes is called absorption. Exogenous chemicals are mainly absorbed through respiratory tract, digestive tract and skin in living environment. People eat for the sky? Food and water are the basis of human existence? So what? Digestive tract absorption is the main way for exogenous compounds to enter the human body.