Air pollution constitutes a significant global health risk, contributing to increased morbidity and mortality. While the detrimental effects of airborne pollutants—such as ozone, particulate matter (PM10, PM2.5), volatile organic compounds (VOCs), and oxides—on internal organs are well-documented, the impact on the skin, the body’s largest organ, has been studied less extensively in vivo. The skin acts as the outermost barrier and is recognized as a direct target for these environmental pollutants, which can cause oxidative stress, impair the skin barrier, and exacerbate existing skin conditions.
Although in vitro studies have demonstrated that individual pollutants can induce inflammation and the production of reactive oxygen species (ROS), ethical constraints severely limit trials that involve direct in vivo exposure to pollution. Consequently, there is a recognized lack of objective tools to measure individual, chronic exposure based on observable skin responses. To enable predictive in vivo trials, especially those supporting cosmetic claims like “antipollution,” researchers need a method to reliably characterize subjects based on their chronic, daily environmental exposure. This study, authored by Perugini, Grignani, and Bleve, addresses this gap by introducing the Exposure Intensity Index (EII), a novel, lifestyle-based framework designed to correlate individual pollution exposure with measurable biophysical changes in the skin.
Methods
The study was a prospective observational trial conducted on 250 Caucasian women residing in the highly polluted Lombardy region of Northern Italy. The methodology consisted of two phases: first, subjects completed a comprehensive, 18-question survey detailing socio-demographic features and daily habits (including living area, proximity to traffic/industry, and smoking habits), from which a non-weighted numerical EII score (ranging from 4 to 18) was derived. Second, eligible subjects (193 for hydration, 209 for inflammation) underwent instrumental evaluation of skin parameters on the cheekbone area. Specific non-invasive techniques utilized were Corneometry to assess Stratum Corneum (SC) water content (hydration) and reflectance spectrophotometry (Mexameter) to measure the erythema index (EI, reflecting inflammation). Statistical analysis, including Spearman’s rank correlation, was applied, adjusting for age (stratified at 50 years old) due to its significant influence on the measured skin parameters.
Key Findings
The results of the correlation analysis provided crucial insights into how lifestyle-derived pollution exposure relates to cutaneous changes:
• Correlation with Inflammation: A strong positive correlation emerged between higher EII scores (indicating greater pollution exposure) and higher erythema index values in both age groups studied (under 50 and 50+), suggesting a link between chronic exposure and subclinical cutaneous inflammation.
• Erythema Sensitivity: The erythema index appeared to be a more sensitive marker of pollution-related exposure compared to SC water content. The positive trend relating EII score to increased erythema intensity was clearly discernible when combining data from both age groups.
• Hydration Variability: Although previous research links pollution to dryness, the relationship between EII and Stratum Corneum (SC) water content values was complex and inconsistent. The variability observed, particularly among older women, suggests that factors like regular beauty routines (e.g., moisturizing practices) may compensate for or mask any subtle effects pollution has on skin hydration.
• EII Validity: The EII successfully demonstrated its capability to capture differential exposure patterns, showing that scores differed significantly among subjects residing in distinct geographical areas (urban vs. rural/countryside) within the study region.
This research successfully introduces the Exposure Intensity Index (EII), providing an exploratory framework that moves beyond isolated environmental measurements or in vitro models by offering an integrated, real-life model of exposure-response dynamics.
The primary novelty of the EII lies in its non-invasive, cost-effective nature and its ability to differentiate individuals based on lifestyle-related exposure, correlating self-reported data with inflammation-related skin biophysical parameters, specifically erythema. This correlation aligns with existing evidence that airborne toxicants can induce irritation and inflammatory responses.
The future implication of this research is significant for both basic scientific investigation and the cosmetics sector. EII holds substantial potential as a preliminary tool for subject selection in in vivo efficacy studies, especially for products making anti-pollution claims. By recruiting subjects with a well-established chronic exposure background defined by the EII score, the reliability and clarity of efficacy results in cosmetic testing could be enhanced. Further validation is needed, however, through larger and more diverse cohorts, while recognizing the inherent limitation introduced by the subjective nature of self-reporting.
Link to the study: https://www.mdpi.com/2079-9284/12/5/215
