Background: Multiple Chemical Sensitivity (MCS) is a rising concern worldwide, particularly in Japan, where the number of individuals with high chemical sensitivity has increased by 500% over the past decade, with the current prevalence estimated to be 1 in 7 people. The exposure to fragrances in households continues to rise, as fragrance chemicals are found in nearly every household product. Limonene, an ingredient common to 77% of fragrance products, converts to formaldehyde in the air, which potentially implicates it in MCS pathology due to the generation of oxidative stress.[1][2]

Purpose: This study aims to investigate the relationship between a fragrance ingredient, formaldehyde generation, oxidative stress, and MCS pathology.

Methods: Over 40 Japanese detergents and fabric softeners were assessed for common ingredients, with limonene identified as the most prevalent. Gas detection methods were employed to measure the amount of formaldehyde generated from limonene.

Results: Heating limonene to 37°C produced formaldehyde concentrations exceeding indoor air quality standards, when the concentration of limonene was around 400 ppm (in the range of an easily detectable to strong odor). The concentration of formaldehyde surpasses permissible regulatory indoor standards and could increase oxidative stress in airway tissue and the blood.[3] This toxic effect potentially suggests a pathological mechanism for triggering MCS symptoms.

Conclusions: These findings highlight the potential role of common fragrance ingredients in formaldehyde generation in households. The formaldehyde concentration reached exceeded indoor safe standards, which presents a necessity to investigate the relationship with MCS pathology further, mediated by changes in oxidative stress levels in airway tissue and blood.[4]

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.