**1. Introduction**

Asthma is a heterogeneous disease characterized by chronic airway inflammation and airway hyperresponsiveness, and the main lesion site is bronchi. It is a threat to public health worldwide and affects people of all ages. According to relevant data, it is conservatively estimated that there are at least 300 million asthma patients in the world, and 380,000 people die of asthma every year. Asthma has become a serious public health problem, bringing great pressure to individuals, families and the society. At the same time, the incidence of asthma is also one of the fastest rising diseases in the world. Data show that the overall prevalence of asthma in both adults and children has been increasing worldwide for the past 20 years. At present, the prevalence of asthma varies greatly among countries in the world, ranging from 0.3–17%, and the incidence of asthma varies in different regions and genders within the same country. Generally speaking, the incidence of asthma is higher in developed countries than in developing countries and higher in urban areas than in rural areas [1, 2].

The mechanism of asthma is complicated, and its pathogenesis has not been fully understood. Currently, asthma is considered to be a heterogeneous disease with the combined effects of gene and environment [3]. Asthma is a polygenic disease, and hundreds of asthma susceptibility gene loci have been found, which are related to the molecular mechanism and pathophysiological manifestations. Epigenetics regulate asthma between environmental and genetic factors through DNA methylation, histone modification, and regulation of non-coding RNA [4]. At the same time, the complex role of airway and gut microbiome in the development and severity of asthma has also been recognized [3].
