There are three main causes of allergic rhinitis: genetic factors, environmental factors and exposure to allergens. I. Allergies caused by heredity People with a family history of allergic reactions are susceptible to this disease. Patients’ families mostly have a history of asthma, urticaria or drug allergy. Children with a family history of asthma or allergic rhinitis have a 2-6 times higher risk of developing allergic rhinitis and a 3-4 times higher risk of developing asthma than the general population. Previously, this patient was called an atopic individual with a higher than normal ability to produce IgE antibodies. However, in recent years, some authors have found no significant difference in the incidence between twins and the general population. Allergic constitution is genetically related and is usually genetic in origin. Most of the patients with allergic rhinitis have a family history of allergy, but in recent years, due to the accelerated industrialization and increased atmospheric pollution, some people who were originally non-allergic have evolved into allergic. Most of the children first develop rhinitis and then asthma; a few of them have asthma and then rhinitis; or both of them occur simultaneously. It is evident that there is a clear correlation between the development of allergic rhinitis and asthma. Usually, whether a high-risk person develops the disease and its manifestation in the respiratory tract after the disease is related to the genetic susceptibility, the type, duration and intensity of exposure to allergens. The susceptibility of the nasal mucosa arises from the frequent stimulation of antigenic substances (automobile exhaust, cosmetics, decorative materials and food additives), and in recent years, due to the accelerated industrialization and increased atmospheric pollution, some people who were originally non-allergic have evolved into allergic. However, the degree of susceptibility depends on the number of mast cells and basophils in the nasal mucosa and the ability to release chemical mediators. It has been confirmed that the number of these cells in the nasal mucosa of patients with allergic rhinitis is not only higher than that of normal people, but also has a strong ability to release chemical mediators. The antigenic substances that stimulate the body to produce IgE antibodies are called allergens. The allergen substance re-enters the nasal mucosa and binds with the corresponding IgE to cause allergic reaction. Allergens that cause the disease are classified into two categories according to the way they enter the body: inhalation and food: 1. Inhalation allergens are inhaled into the nasal cavity through breathing. These allergens are mostly suspended in the air. (1) Pollen Not all plant pollen can cause disease. Only those pollen with large pollen volume, extensive vegetation, strong allergens and wind-borne are most likely to become allergens. Due to differences in vegetation species, pollen with allergenicity varies from region to region. For example, in Northern Europe, pollen from birch trees and ladder grasses are the main pollen; in North America, ragweed is the main pollen; in Japan, cedar tree pollen is the main pollen; in China, the vast area, allergic pollen is not consistent from region to region, the northern region is dominated by wild artemisia pollen, but ragweed is found in the north and south of the river, which should be taken seriously. In recent years, it is believed that with the continuous development of industrialization, the concentration of sulfur dioxide and other harmful substances in the air has increased, which can cause the protein structure of the pollen surface suspended in the air to mutate, so that the pollen that originally does not have allergic origin also has a strong allergic origin. This may be one of the main reasons for the significant increase in incidence. There is a significant seasonality in the types and levels of pollen in the air, with the peak of pollen dispersal in spring and summer/autumn. (2) Fungi are very widely distributed in nature, mainly in soil and decaying organic matter. Its mycelial spores are all allergic, but the spores are stronger. Spores can be widely spread by wind, the number in the air is sometimes higher than pollen, rural than urban. Indoor high temperature and dark and humid is conducive to fungal growth. Indoor ornamental flower pots in the soil also often become a good place for fungal growth. (3) House dust mites belong to the phylum Arthropoda (spiders). Adult mites are usually 300-500μm in size and are found in all corners of the house, including the dust in mattresses, pillows and sofa cushions. The excrement, eggs, debris and disintegrated limbs of mites can be the source of allergic reactions. (4) Animal dander Animal dander is one of the strongest allergens. Susceptible individuals can be sensitized if they have long-term contact with the animal in question. After sensitization, even a small amount of dander can trigger nasal symptoms. The animal dander that causes respiratory allergic reactions mainly comes from animals in close contact with people, such as domestic pets (ornamental dogs, cats), domestic dogs, cattle, horses and sheep. (5) Feathers Feathers in poultry or bedding, pillows and clothing, and feathers shed by domestic ornamental birds can be sources of allergic reactions. (6) House dust is one of the common allergens that cause perennial rhinitis. Its composition is quite complex, a hodgepodge of substances, including animal, plant and chemical substances. 2. Ingested allergens are allergens that enter the body from the digestive tract and cause nasal symptoms. The way it acts on the nasal mucosa is very complicated and still not very clear. Milk, eggs, fish and shrimp, meat, fruits, and even certain vegetables can become allergens.