Currently, allergens are mostly classified into two categories: inhalational and ingestive. Inhaled allergens: mostly refers to allergens suspended in the air. Inhaled allergens can be divided into indoor and outdoor allergens. The most important indoor allergens are dust mites, molds, pets and insects. In close contact with the human body, bedding, clothing and pants, dust mites and their excretions are more; in a humid, warm, poorly ventilated indoor environment, mold is easy to grow; a variety of insects such as crickets, flies, moths – especially cockroach excrement are common allergens. Outdoor allergens may be present in spring, summer, fall and winter. These include: elm, poplar, acacia, birch, and overhanging trees. In addition, aromatic hydrocarbon particles in oil exhaust and formaldehyde generated by home renovation need attention. Although they are not allergens (allergen is a protein), they are the strongest irritants for seasonal allergic rhinitis attacks. Common inhalation allergens are introduced as follows: 1. Pollen: Research has shown that with the continuous development of industrialization, the concentration of harmful substances such as sulfur dioxide in the air has increased, which can make the surface protein structure of pollen suspended in the air mutate, so that the original non-allergenic pollen also has strong allergenicity, leading to a significant increase in the incidence of allergic diseases. Not all plant pollen can cause morbidity. Often pollen with large pollen volume, extensive vegetation, strong allergenicity and wind-borne pollen are most likely to become allergens. Due to the existence of plant species and regional differences, the distribution of pollen allergens varies. In Northern Europe, birch and timothy are dominant; in North America, ragweed is dominant; in Japan, cedar pollen is dominant; in China, with its vast territory and large latitude and longitude, allergenic pollen is not uniform from region to region, with wild artemisia pollen dominating in the northern region and ragweed appearing in the north and south of the country. There are significant seasonality in the type and content of pollen in the air, and spring and summer and autumn are the peak of pollen dispersal. 2, fungi: nature is very widely distributed, mainly in the soil and decay of organic matter, its mycelium, spores can have allergenicity, with spores as strong. Spores are widely spread by wind, the number in the air is sometimes higher than pollen, rural concentrations are higher. The most common species of fungi is the genus of single-spored mold, cross-streptomycetes, Penicillium, Aspergillus and yeast genus. Among them, Aspergillus and Streptomyces have significant seasonality, and the number of spores in the air peaks more in the summer. Indoor high temperature and darkness and humidity is conducive to fungal growth. Indoor ornamental flower pots in the soil often become a good place for fungal growth. 3, house dust mite: belong to the Arthropoda spider class. Adult mites are generally 300μm-500μm in size and are mainly found in the corners of people’s homes, most often on mattresses, pillows and sofa cushions. The excrement, eggs, debris and disintegrated limbs of mites can all be allergens. 4. Animal dander: Animal dander is one of the common allergens. Susceptible individuals can be sensitized if they have long-term contact with the animal in question. After sensitization, if re-exposure to 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 (dogs, cats), domestic dogs, cattle, horses and sheep. 5, feathers: poultry or bedding, pillows and clothing in the feathers, domestic ornamental birds shed feathers, can be allergens. Ingested allergens: refers to allergenic substances that enter the body from the digestive tract and cause nasal symptoms. The mechanism of its action on the nasal mucosa is still unclear. Milk, eggs, fish and shrimp, meat, fruits and even vegetables can be allergens.