摘要
Asthma and allergies have been increasing worldwide during the last 5 decades.Fifty years ago,prevalences of asthma and allergies were less than 1%;compared to today when up to 1/3 of children in some regions have been diagnosed with asthma.The burden on families and the health care system is great.The increase in asthma,rhinitis,and eczema(whether atopic
Asthma and allergies have been increasing worldwide during the last 5 decades. Fifty years ago, prevalences of asthma and allergies were less than 1%; compared to today when up to 1/3 of children in some regions have been diagnosed with asthma. The burden on families and the health care system is great. The increase in asthma, rhinitis, and eczema （whether atopic or not） among children has been demonstrated by the numerous ISAAC studies （International Study on Asthma and Allergies in Children） [1,2]. In some recent studies, the increase has been found to slow or even reverse in some countries. In spite of a large interest from medical and environmental sciences （ambient air）, reasons for the increase in allergic dis eases are not clear. It is acknowledged that the increase cannot be due to genetic changes, as the time period is too short. In stead it appears that environmental changes are responsible. But what environmental changes？ Outdoor air has, in most west ern countries, been radically improved during the time that asthma and allergy prevalences have increased [3]. The ＂hygiene Hypothesis＂ holds that the environment today is ＂too clean＂： children are not exposed to dirt, as they once were, so that the immune system has too little to do, and starts reacting to pollen, cat allergen and other allergens instead of to pathological microbes. However, as of this writing （March 2013） there are 179 reviews of the scientific literature on the ＂hygiene hypoth esis＂ and the general conclusion is that it cannot explain the increase （or decrease） in these diseases or specific allergies, see e.g. [4]. The food hypothesis, a variant on the hygiene hypothesis, holds that changes in food and preparing food have caused changes in intestinal microbial flora in a way that facilitates the development of asthma and allergies. However, no evidence has emerged, even from large scale studies, that changes in food or drink are a major cause. Several other hypotheses have been offered and discussed. The most common is that the increase might simply be due to medical practitioners being updat ed so that they diagnose these diseases more often. However, many studies have shown an increase in symptom prevalence greater than that of doctors＇ diagnoses. Several risk factors have been identified, including exposure to environmental tobacco smoke （ETS） or pets, lack of breastfeeding, caesarian delivery, but no single risk factor can explain the rapid increase. None theless, the cause must be something that has changed in our environment. Exposure （inhalation, ingestion） to indoor air is by far the largest （by mass） that humans experience, especially during ear ly childhood. The home accounts for more than 50% of the exposure during life, and for about 75% during infancy. There have been dramatic changes both qualitatively and quantitatively in indoor air exposure during the last decades, namely, more energy efficient buildings leading to less ventilation; new building and furnishing materials, and new consumer products. In 2000, Swedish researchers started an extended study of small children on both the prevalences of asthma and allergies, and risk factors in the home environment in SwedenThe first author of this editorial is one of the leading researchers. Then, such research continued in Bulgaria, Singapore, USA （Texas）, South Korea, Denmark. We now continue that in mainland of China. Phase I consists of crosssectional studies to estimate prevalences as well as risk and protective factors; and Phase II compares the home environments of sick and healthy （normal） children in casecontrol studies. Phase II has been performed in Sweden, Bulgaria, Singapore and Denmark. The main findings thus far are that risk factors include genetic disposition （family history of allergy and/or asthma）, pres ence of ＂modern＂ chemicals in the home, and a lack of ventilation. Findings differ slightly between countries and regions, and among the cities reported on in this special topic. The strongest risk factors for asthma in small children have been identi fied in Sweden as certain phthalates and glycol ethers [5,6]. These new chemical compounds are used in ＂modern life＂ prod ucts such as plastics, water based paints, hygiene products, toys and skin lotion and have been detected in high concentrations in home environments. Many of these chemicals are also endocrine disruptors （EDCs） that have health outcomes in addition to asthma and allergy [7]. Accordingly, ＂modern＂ health effects like asthma, may be due to ＂modern＂ exposures, rather than to a lack of ＂old expo sures＂ like dirt, microbes, mold nanoparticles or PM2.5, entities which have always been in our environment, but which can now be measured. There were no plasticizers 60 years ago, but today, exposure to such ＂modern＂ materials is inescapable. Initially, asthma and allergy prevalences mainly increased in western developed countries with high GDP/capita countries （e.g. western Europe） but not in countries with lower GDP/capita （e.g. eastern Europe）. Today many developing countries have a high prevalence of asthma, so perhaps it is not how rich a society is, but what ＂modern＂ exposures they have.
