From October 2000 to March 2021, we examined the clinical features of 349 outpatients with SHS, MCS and EHS (16 years and older) who initially visited our hospital with symptoms. A diagnosis of MCS was made based on the “1999 Consensus”. The average age of the subjects was 47.6 +/-13.3 years, with a male to female ratio of 1:4.82. However, the male-to-female ratio of 34 children aged 15 years or younger was 1:1.15 (p<0.001). A review by disease type indicates that SHS accounted for 22.3% of the cases, decreasing after 2007, with 69.2% thereof progressing to MCS or MCS+EHS. The trend shows that EHS associated with MCS has been on the rise since 2011. There was a significant difference in the male-female ratio between adults and children. The results also suggest that there more females than men develop the disease at an older age. There is a concern that MCS and EHS will increase going forward, so some form of countermeasure is desired.

In recent years, the rapid increase in the number of patients with environmental hypersensitivity has become a worldwide problem, and although it has been pointed out that the condition is closely related to allergic diseases, its pathogenesis remains to be elucidated. Environmental hypersensitivity is a health disorder characterized by a variety of systemic symptoms, including autonomic and endocrine symptoms, immune and allergic symptoms, chronic pain and fatigue, memory and emotional disorders, and hypersensitivity to external environmental stimuli in daily life. Typical examples include sick building syndrome, multiple chemical sensitivity, and electromagnetic hypersensitivity. Over the past 30 years, I have conducted multifaceted epidemiological investigations, including the development of a Japanese translation of the international common questionnaire to evaluate environmental hypersensitivity, the confirmation of its reliability and validity, and the setting of screening thresholds unique to Japan. In this paper, I describe the latest findings on environmental hypersensitivity and introduce some of the epidemiological studies conducted by the authors in Japan using the international common questionnaire.

A questionnaire survey was conducted of elementary school students (6-12 years of age) in Joetsu City for multiple chemical sensitivity-like symptoms (MCS-like symptoms) in July 2005. In July 2010 and July 2017, re-surveys of elementary and junior high school students (6-15 years of age) were conducted to assess any temporal changes. The number of valid responses was 10,348, 14,024, and 7,224 in the 2005, 2010, and 2017 surveys, respectively. The results showed that the number of students with MCS-like symptoms was 979 (9.5%), 1,734 (12.4%), and 874 (12.1%) in 2005, 2010, and 2017, respectively. The results showed that the proportion of elementary and junior high school students with MCS-like symptoms increased with age. In this paper, I describe in detail the content of the questionnaire, the number of students with MCS-like symptoms, and the prevalence rate of each symptom used to evaluate students with and without MCS-like symptoms.

Chemicals released from detergents, shampoos, cosmetics, and other products have caused serious health problems in recent years. Patients complain of distress from fragrances and other substances emitted from the clothing and bodies of those nearby on trains and in the workplace, rendering them unable to engage in normal activities. This article gives basic information related to the problem of chemical sensitivity and discusses the purification of air containing volatile organic compounds released from detergents using an air purification system developed by the authors.

Due to chemical exposure, multiple chemical sensitivity (MCS) has become a severe problem. The mechanism of MCS, however, still needs to be clarified. This paper considers the role of science and policies regarding MCS. The Japanese government has taken measures to prevent and deal with MCS, such as setting guidelines for indoor chemical concentrations and registering the disease name for health insurance claims. However, since MCS patients have differing symptoms, a uniform policy is difficult to implement, so we must act with sympathy and empathy. MCS is no longer a rare disease; like hay fever, it can affect anyone. In the future, it is necessary to prevent patients from becoming severely ill and to prevent the occurrence of new MCS patients.

Multiple Chemical Sensitivity (MCS) is a controversial disorder characterized by a recurrent set of diverse clinical manifestations, involving a broad spectrum of organ systems, that are induced by environmental chemicals at doses far below those usually harmful to most persons. To prevent MCS and other adverse effects on human health from environmental chemicals, concentration thresholds of frequently used chemicals in homes, workplaces, and schools are defined by several legal and administrative regulations. However, only a small percentage of the tens of thousands of environmental chemicals in use have been evaluated for toxicity and accumulation, and recent amendments of laws and regulations are directed toward comprehensive management of chemicals as a whole.

In order to comply with the standard school size required by law, Japanese municipalities have been dividing and consolidating schools as the student population changes. Standard school-size laws require 12–18 classes per school, but lack an empirical basis. In this paper, we examine the adequacy of standard school-size laws from an expenditure perspective and identify the number of schools required to minimize school operating costs. The result shows that there are economies of scale between elementary or junior high school costs and the number of schools or school sizes. Estimations indicate that minimized costs are achieved when there are 103.0 elementary schools and 20.4 junior high schools per municipality, with 521.9 students per elementary school and 555.2 students per junior high school. These results lead us to the conclusion that (1) a shift to a broader education administration area would be desirable for fiscal efficiency and (2) these numbers are coherent with the school-size laws. The confirmation of this point is one of the important contributions of this study.