There is an interesting epidemiological trend in the last two decades that the prevalence of asthma, allergies, and obesity is significantly higher in developed Western countries than in developing countries, with an increasing trend year by year, and this increasing trend is positively correlated with improved public health facilities, improved sanitation and quality of life, smaller families, and low infection rates in Western countries; the cause of this phenomenon is difficult to explain by genetic factors alone, because Genetic studies have shown that genetics has remained largely unchanged over the last few decades, so changes in environmental factors may have a greater impact on the increased incidence of obesity than genetic changes. Studies have shown that microbial exposure can influence the occurrence of asthma, allergies, and obesity, and that the main reason for the increased incidence of obesity in Western developed countries may be a reduction in microbial exposure caused by improved medical and environmental conditions, which is the hygiene theory that has become very popular in recent years. Playing in the mud, rolling in the grass, catching tadpoles, building castles, digging caves, catching bugs and other games that modern parents consider “dirty” can keep children away from allergic rhinitis and allergic asthma. Allergic rhinitis accounts for a large percentage of white-collar children in urban areas. Parents are particularly concerned about hygiene, and the toys and fruits that their children touch and eat are strictly disinfected, and the rooms are spotless. They also rarely take their children to play outdoors for fear of transmitting diseases. Doctors believe that these delicate babies are exposed to an environment that is so clean that their bodies lose resistance to the outside world instead. Epidemiological surveys have found that children from large families, children who entered nursery school early, and children who had been infected with tuberculosis or measles have a low incidence of allergic rhinitis, asthma, and other allergic diseases. This is due to the fact that exposure to each other in the nursery or in the extended family gives children a higher chance of getting respiratory infections. Conversely, the less exposure to infectious agents or respiratory infections, the higher the incidence of their allergic diseases. When you see the above, I believe many parents will feel strange, clean is wrong? There is nothing wrong with being clean, but cleanliness should not be a degree, otherwise, it is counterproductive.