Background: In recent years, fragrance pollution triggered by common household items has become a global concern, contributing to the increasing prevalence of Multiple Chemical Sensitivity (MCS) worldwide [1]. Despite the rising prevalence, there is a lack of researchers and diagnostic criteria for MCS, hindering effective diagnosis and treatment.

Purpose: This study proposes several investigations and experimental methods to elucidate the factors contributing to MCS and discusses the current status of diagnostic criteria for MCS, which remain unidentified.

Methods: We estimated the number of individuals affected by MCS based on existing studies [2] and identified fragrance ingredients commonly used in everyday products. Additionally, we explored methods to visualize invisible fragrances and considered how physicians should diagnose MCS.

Conclusions: At present, more than 16 million people in Japan (about 1 in 7) are estimated to suffer from “MCS” or have “High Sensitivity” or “Semi-High Sensitivity” to Chemical Substances. Recent developments in microencapsulation technology suggests that sustained fragrance release may contribute to the increase in MCS prevalence by continuously emitting hazardous substances [3], similar to allergic reactions seen in individuals with pollen allergies. Therefore, MCS should be recognized as a condition that anyone can develop, similar to pollen allergies. To prevent MCS, essential measures such as refraining from releasing fragrances in shared spaces are indispensable.