Associations between skin microbiome, skin physiological parameters and dietary intake across adulthood: a cross-sectional observational study

Research exploring the influence of diet on the skin microbiome and its role in skin aging is limited (1,2) . This study aimed to investigate age-related changes in skin microbiome and physiological parameters across adulthood, and to examine associations with habitual diet, anthropometry, demographics, and use of skin care products or medications. Institutional ethical approval was obtained (0617-2025-Apr-HSET). Adults were recruited across 5 age groups through word of mouth, flyers and social media. Exclusion criteria included ongoing intensive medical treatment (e.g., chemotherapy), current or recent smoking (stopped <1 year ago), and allergies to tape strips and/or swabs. Anthropometric measures included weight (kg), body mass index (BMI) (kg/m2), waist circumference (cm) and body fat (%). Habitual dietary intake over the proceeding 4 weeks was assessed using the validated eNutri web app (3) capturing fluid, food, nutrient and supplement intake. Skin physiological measures were conducted on the non-dominant forearm using validated instruments to measure barrier function (indicated by lower trans-epidermal water loss [TEWL]), stratum corneum cohesion (indicated by protein removed from stratum corneum), skin hydration and skin surface pH. Skin swabs from the inner elbow were used for DNA extraction and 16S metagenomic sequencing. Bacterial diversity (observed species, Shannon index), abundance, and phylum level composition were determined. Statistical analysis included Pearson’s or Spearman’s correlation coefficients, Mann–Whitney U and Kruskal–Wallis tests for non-parametric comparisons, and general linear models to identify predictors of skin physiological parameters and skin microbiome. Forty-one adults, aged 20-92 years, 30 female, 11 male (median BMI 24.9kgm2, IQR 6.5) completed the study. There was a significant negative correlation between TEWL and age (r=-0.431, p=0.012), and alcohol intake (% total energy) (r=-0.325, p=0.002) whereas iron intake (mg/d) was positively associated with TEWL (r=0.311, p=0.028). Skin barrier function was significantly higher in females (p=0.008). This indicates that older age, higher alcohol consumption, lower iron intake, and female sex may be associated with improved skin barrier function. There were also significant negative correlations between protein removal from the stratum corneum and both age (r=-0.371, p=0.007) and fruit intake (g/day) (r=-0.480, p=0.013), indicating stronger cohesion in younger individuals and those with higher fruit intake. Skin hydration was negatively associated with body weight (r=-0.343, p=0.020) and positively associated with dietary fibre intake (AOAC g/d) (r=0.468, p=0.001). Additionally, body weight (kg) was positively associated with skin microbiome abundance (r=0.536, p=0.002) and negatively associated with microbial diversity (observed species) (r=-.513, p<0.001). This study shows it is feasible to explore how age, anthropometry, and diet relate to skin physiology and microbiome in healthy adults. Our findings suggest that these factors influence different aspects of skin health in distinct ways. A larger powered cross-sectional study is warranted to validate these findings.