1. Genetic factors Asthma is a disease with complex traits and a polygenic genetic predisposition. It is characterized by: (1) episodic incompleteness, (2) genetic heterogeneity, (3) polygenic inheritance, and (4) synergistic effects. 2. Allergens The most important triggering factor for asthma is probably inhalation of allergens. (1) Indoor allergens
House mites are the most common and harmful indoor allergens, and are an important factor in the development of asthma worldwide. More than 90% of the mites are found in house dust, and house dust mites are the predominant mite in persistent humid climates. The main antigens are DerpI and DerpII, and the main component is cysteine protease or tyrosine protease. House pets such as cats, dogs and birds release allergens in their fur, saliva, urine and fecal secretions. Cats are the most important allergens among these animals, and their main allergen component, feldl, is present in their fur and sebum secretions and is the main risk factor for acute asthma attacks. Cockroaches are common indoor allergens in Asian countries; cockroaches American cockroach, German cockroach, Oriental cockroach and black-breasted cockroach are commonly associated with asthma, with the black-breasted cockroach being the most common in China. Fungi are also indoor air allergens, especially in dark, humid and poorly ventilated areas, such as Penicillium, Aspergillus, Streptomyces, Mycosphaerella and Candida. Among them, Streptomyces has been identified as a risk factor for asthma. Common outdoor allergens: Pollen and grass pollen are the most common outdoor allergens that cause asthma attacks. Woody plants (tree pollen) often cause asthma in the spring, while grasses and atrazine pollen of grassy plants often cause asthma in the fall. In the eastern part of China, ragweed pollen is the main type of pollen; in the north, artemisia is the main type. (2) Occupational allergens
Common allergens that can cause occupational asthma include grain flour, flour, wood, feed, tea, coffee beans, silkworms, pigeons, mushrooms, antibiotics (penicillin, cephalexin) isocyanates, phthalic acid, rosin, reactive dyes, persulfates, ethylenediamine, etc. (3) Drugs and food additives
Aspirin and some non-corticosteroid anti-inflammatory drugs are the main allergens of drug-induced asthma. Food additives such as salicylates, preservatives and coloring agents can also cause acute asthma attacks. Royal jelly oral solution is a food widely used as a health supplement in China and in countries and regions in Southeast Asia. It has been confirmed that royal jelly can cause acute asthma attacks in some patients as a result of IgE-mediated allergic reactions. (1) Air pollution Air pollution (SO2, NO) can cause bronchoconstriction, increased transient airway reactivity and enhanced response to allergens. (2) Smoking
Cigarette smoke (including passive smoking) is a major source of indoor triggers and is an important asthma trigger, especially for children with asthma whose parents smoke, often causing asthma attacks due to smoking. (3) Whistling viral infections
Whistling viral infections are closely related to asthma attacks. Bronchial viral infections in infants have received particular attention as an initiating cause of asthma onset. Common viruses of the whistle tract infections include whistle syncytial virus (RSV), adenovirus, rhinovirus, influenza virus, parainfluenza virus, coronavirus, and some enteroviruses. The viruses associated with adult asthma are predominantly rhinoviruses and influenza viruses; whistle syncytial virus, parainfluenza virus, adenovirus, and rhinovirus are closely associated with asthma attacks in children. Syncytial viruses are the main pathogens in the first year of life and account for 44% of infectious asthma in children under 2 years of age and also more than 10% of asthma in older children associated with their infection. It has been reported that nearly 100% of patients with asthma or capillary bronchitis after RSV infection have IgE attachment to epithelial cells. Asthma occurred in 42% of children hospitalized for acute RSV infection after 10 years. (4) Perinatal fetal environment
The fetal thymus at 9 weeks of gestation can already produce T lymphocytes, and at weeks 19-20, B lymphocytes are already produced in various fetal organs. If the mother is already atopic and is exposed to a large number of allergens during pregnancy (e.g., lactoglobulin in milk, ovalbumin in eggs, or DerpI from mites) or is repeatedly infected with whistling viruses, especially syncytial viruses, her Th2-regulated allergic reactions may be exacerbated, increasing the likelihood of postnatal allergic reactions and asthma development. In addition, the amount of polyvalent unsaturated fatty acids consumed in the body during late pregnancy will affect the production of prostaglandin E, which may be relevant for Th2 cell-regulated allergic reactions. Maternal smoking during pregnancy will certainly affect fetal lung function and susceptibility to later onset of wheezing. (5) Other strenuous exercise, climate change and various non-specific stimuli such as inhalation of cold air, distilled water droplets, etc. In addition, psychological factors can also trigger asthma.