Food intolerance is a complex metabolic disease. It occurs when the immune system treats one or more foods that enter the body as harmful substances, thus generating an excessive protective immune response against these substances and producing food-specific IgG antibodies, which form immune complexes with food particles and may cause inflammatory reactions in all tissues and manifest as symptoms and diseases of various systems throughout the body. Food intolerance is currently a research hotspot in various countries, and its application is rapidly spreading worldwide. I. Pathogenic mechanism of food intolerance Although there is still disagreement on the mechanism of food intolerance, the fact of its existence and its consequences are well recognized. According to Dr. Fooke, theoretically, after entering the digestive tract, food should be digested and broken down to the level of amino acids, glycerol and monosaccharides so that it can be fully converted into energy for human needs, but this is not the case. Many foods, including some of our most commonly consumed foods, are not fully digested by the body because they lack the appropriate enzymes and enter the intestine as peptides or other molecules where they are recognized by the body as foreign substances, leading to an immune response that produces food-specific IgG antibodies. the IgG antibodies bind to the food molecules to form immune complexes that are eliminated by the body as waste products from the kidneys. In the kidney, because certain immune complexes cannot pass through the glomerular filtration membrane, they block the filtration structures of the kidney, resulting in increased glomerular filtration pressure, secondary to increased blood pressure, dilated blood vessel walls and cholesterol deposition. Human waste fluid cannot be excreted normally through the kidneys and is retained in the tissues, especially in fat cells, eventually leading to edema and obesity. If the diet is not changed in time, intolerant foods will continue to form complexes and aggravate the existing symptoms. The immune system becomes overloaded, resulting in a series of symptoms and diseases in various systems of the body, including hypertension, obesity, headache or migraine, chronic diarrhea, fatigue, infection and other diseases in various systems. Food intolerance is an IgG-mediated immune response that can occur at all ages, and its main manifestation is long-term chronic symptoms caused by food intolerance. Studies have shown that food intolerance can affect all systems of the body, for example, in the gastrointestinal system, it can occur in all digestive organs from the mouth to the anus, with common symptoms such as bloating, dyspepsia, diarrhea, abdominal pain, etc. The disease is prolonged and the clinical manifestations can be both localized in the digestive tract and in areas far from the digestive tract, and the diagnosis is often delayed due to the lack of effective diagnostic tools that are ignored by the clinic. Food intolerance is also a cause of irritable bowel syndrome IBS, with 33% to 66% of IBS patients considered to have food intolerance. The correlation between food and enterocolitis is also quite high in patients with food-induced enterocolitis. Symptoms or diseases such as these often have a serious impact on the patient’s work and life, and if they are treated with medication for this reason, not only will the source of the disease not be eradicated, but it may also place a heavy financial burden on the patient and family. Patients with food intolerance can develop intolerance to four to five or more foods at the same time. Their symptoms usually appear a few hours to a few days after eating, and long-term consumption can also cause chronic symptoms, and since their symptoms are not specific, it is difficult for patients to diagnose themselves. According to the British Allergy Society, up to 45% of the population has varying degrees of intolerance to certain foods, and the incidence is higher in infants and children than in adults. In a study conducted by the YORK Nutrition Laboratory, 2,567 British people with suspected food intolerances were investigated and approximately 69% of these cases were classified as chronic, and a summary analysis of the patient’s symptomatology in each system was conducted. Table 1 1 Symptom manifestation of patients in each system Systemic symptoms Symptom manifestation Incidence % Digestion Chronic diarrhea, abdominal pain, ulcers, dyspepsia, etc. 44 Skin Rash, erythema, pruritus, etc. 16 Nervous Migraine, poor sleep, etc. 12 Respiratory Asthma, etc. 10 Musculoskeletal Arthralgia, etc. 7 We summarized the possible symptoms as follows: 1. Digestive system: nausea, abdominal pain, diarrhea, halitosis, belching, flatulence. 2. Skin system: eczema, facial blisters, brittle nails and hair, urticaria, dry skin. 3, nervous system: anxiety, confusion, depression, irritability. 4, respiratory system: asthma, chronic cough, sore throat, increased nasal discharge, postnasal mucus secretion, chronic sinusitis. 5, musculoskeletal system: arthritis, joint pain. 6.Genitourinary system: frequent urination, urgent urination, vaginal itching, abnormal vaginal secretions. 7, cardiovascular system: chest pain, arrhythmia, hypertension, rapid heartbeat. 8, other aspects: fatigue, dizziness, headache, sleep difficulties, obesity, teeth grinding. It can be seen that almost all the symptoms may be related to food intolerance. Third, the relationship between food intolerance and some diseases 1, food intolerance and IBS: IBS is the earliest disease that may be related to food intolerance found. It is a power disorder that involves the entire digestive tract and can cause recurrent upper and lower gastrointestinal symptoms, including different degrees of abdominal pain, constipation or diarrhea, abdominal fullness, etc. The cause is still unknown. Many clinicians have long suspected that IBS may be related to diet in some way. In fact, in recent years, many scientific experiments in Europe have confirmed that IBS is a symptom of consumption of specific foods or condiments. The relationship between lactose intolerance and IBS received the earliest attention. Patients are often clinically affected by gastrointestinal reactions such as diarrhea and abdominal pain after consuming milk or dairy products. According to studies, the rate of gastrointestinal reactions after milk consumption is particularly high in the Chinese population, exceeding 10%. An experiment was conducted at Turku University in Finland to study the relationship between IBS and lactose intolerance. They selected 101 lactose intolerant and 326 lactose digestible individuals from a healthy population and observed their symptoms by giving lactose-containing foods. It was found that IBS symptoms occurred in 15% of the total 427 subjects, of which 1/3 were lactose intolerant. Of these lactose intolerant subjects, half were lactose intolerant and half were lactose digestible. In this trial, the rate of lactose intolerant people with IBS was the same as the rate of lactose intolerant people in this subject group 24%, but the rate of lactose intolerant people with IBS was 60%, which was significantly higher than the rate of such people in the subject population 27%, and the prevalence was significantly higher in women and children than in other groups. It is clear from this trial that there is a high correlation between lactose intolerance and IBS in children and women. Attempts have been made to alleviate and treat IBS through selective control of diet, and studies in the United States have confirmed that IBS symptoms in children with periodic abdominal pain can be effectively reduced by avoiding lactose intake as a substitute for medication. Although we have established that IBS symptoms are associated with specific foods, these foods are not limited to lactose and a range of foods that interact with the large intestine may be potential mechanisms for the development of IBS. Therefore, in 2003, after careful discussion, experts from the European IBS Disease Collaboration agreed that no generalized dietary control protocol could be given for IBS patients, although dietary control has a very positive effect on treatment. 2. Food intolerance and dermatitis: The symptoms of food allergy and food intolerance are most often manifested in the skin. Fast-onset reactions include rubella, angioneurotic edema, and erythema. Late-onset reactions can be observed with severe rashes many of which are genetic contact dermatitis,. Because late-onset disease is difficult to diagnose, transoral provocation tests are often performed on suspected patients. Among the many symptoms, the most frequent symptom is acute rash, of which 40% to 60% is IgE-mediated food allergy, and food additives have been found to cause chronic rash. The role of food allergy in the pathogenesis of genetic atopic dermatitis is still controversial. However, scientists agree that food allergens can cause genetic atopic dermatitis or progressive skin lesions in infants and children; in adults, genetic atopic dermatitis caused or provoked by allergenic foods is very rare. However, in patients with genetic atopic dermatitis and a history of food allergy, food ingestion can provoke all the symptoms of IgE-mediated allergy, with severe allergic reactions ranging from oral food allergy to systemic allergy. In sensitive individuals, skin symptoms can be induced by food ingestion or by direct skin contact, as in the case of lipophilic food allergens that can invade the skin through hair follicles or when the skin barrier is compromised. In general, tachyphylaxis skin contact reactions can be divided into several categories: there are immune or non-immune contact dermatitis contact dermatitis syndrome,, and allergic and non-allergic eczema protein contact dermatitis caused by food proteins,, and hereditary atopic dermatitis inspired by direct skin contact should be included in the scope. In addition, very rarely, type IV hypersensitivity reactions caused by food and food additives can also cause allergic contact dermatitis. 3. Food intolerance and migraine: For a long time, many clinicians have found a relationship between food intolerance and migraine. Food intolerance can cause norepinephrine secretion, leading to vasoconstriction or diastole and stimulation of the trigeminal nerve, brainstem and cortical pathways. In a trial in Italy back in 1989, scientists selected 41 migraine patients, 38 of whom were treated with dietary modifications, and the results were significant in 25 cases. Among these 25 cases, 24 cases of migraine were caused by food intolerance and 1 case was caused by food allergy. From this trial, it can be found that dietary modification is very helpful to improve the condition. In recent years, many trials have confirmed the importance of diet for migraine in children and adults. Foods that can cause migraine include cheese, chocolate, hot dogs, citrus fruits, monosodium glutamate, fatty foods, ice cream, caffeine extracts, chocolate drinks, white wine and beer. Alcohol consumption in minors can cause periodic headaches. IV. Food intolerance and diagnostic medicine The discovery of the close relationship between food intolerance and many human diseases has provided a new direction for the determination of the etiology of many diseases. Since food intolerance is an overprotective immune response of the human immune system against one or more foods that enter the body and produce food-specific IgG antibodies, the detection of such specific IgG antibodies can determine whether the human body has developed a pathology due to food intolerance, thus providing a new, rapid and reliable method for the diagnosis of traditional diseases. At present, several companies at home and abroad have been engaged in the research of relevant food intolerance detection kits, and some have mature products on the market, which are known to be able to detect nearly 100 kinds of foods. They generally apply the ELISA method, which is to encapsulate the intolerant original of the specific food, and then calculate the IgG antibody concentration of the specimen by adding the test serum, enzyme standard, color development, and finally colorimetric, according to the absorbance value. This work has been carried out in the Department of Dermatology of our hospital, and 14 kinds of foods can be tested. Understanding the phenomenon of food intolerance and determining the variety of food that produces intolerance may identify the real cause of the disease, so that a food restriction plan can be made. By using the method of abstaining from or eating less intolerant foods, we can avoid allowing inappropriate foods to continue to damage the organism, find the source of disease occurrence, and control the continued development of the disease, thereby significantly improving the quality of life of patients.