如果孩子活泼好动,每天疯得一身泥回家,你会不会限制孩子去接触泥土?如果孩子喜欢从地上捡起什么东西就往嘴里放,你会不会因此而很烦恼?的确,泥土中含有很多细菌,孩子吃含有致病细菌的东西就会生病。然而你有没有注意到这样一个事实,一般来说,发达国家的医疗卫生条件要好于发展中国家,因此理论上说,孩子患病的可能性也比发展中国家小。然而事实是,发达国家的孩子更容易受到哮喘和过敏性疾病的困扰,而发展中国家的孩子患这些疾病的概率则小得多。此外,在人口较多的家庭中生活的儿童似乎也更健康,他们患花粉热、湿疹等过敏性疾病的概率都小很多。理论上说,人口越多、儿童被传染的概率就越大,更容易得病。可为什么会出现这样反常的情况呢? If the child is lively and energetic, going crazy every day to go home, will not you limit the children to soil contact? If your child likes to pick up anything from the ground and put it in your mouth, will you be so annoyed? Indeed, The soil contains a lot of bacteria, children eat things that contain pathogenic bacteria will get sick. However, have you noticed the fact that, in general, developed countries have better medical and health conditions than developing countries, so in theory the children are less likely to be sick than the developing countries. However, the fact is that children in developed countries are more susceptible to asthma and allergic diseases, while children in developing countries are much less likely to suffer from these diseases. In addition, children living in more populous households appear to be healthier and have less risk of allergic diseases such as hay fever and eczema. In theory, the larger the population, the greater the probability of children being infected and the more likely they are to get sick. Why can such unusual circumstances arise?