Your Skin Microbiome Ages on a Predictable Clock — and Fungi Are Key

The skin is the body's largest organ and hosts a complex ecosystem of bacteria and fungi, yet it remains understudied as an aging biomarker compared to the gut. This pilot study from Peking University First Hospital set out to comprehensively profile how both the bacterial and fungal components of the skin microbiome evolve across the human lifespan — and to build a predictive model of biological age from microbial signatures.

Researchers collected 160 skin swabs from 80 healthy volunteers divided into four age groups centered at 10, 30, 50, and 70 years. Swabs were taken from two anatomical sites: the sun-exposed forehead and the non-sun-exposed back. DNA sequencing was used to profile microbial communities, and a random forest machine-learning classifier was trained on the resulting data.

Several clear patterns emerged. Fungal diversity was significantly higher in women, while bacterial diversity declined markedly around age 30 in both sexes. The fungus Malassezia dominated skin fungal communities across all groups, but its abundance peaked at age 30 and declined thereafter, with the most pronounced drop seen on the foreheads of women. The dominant Malassezia species also changed with age — M. globosa in children shifting to M. arunalokei in elderly individuals. Bacterial communities transitioned from diverse childhood profiles featuring Pseudomonas and Streptococcus to Cutibacterium dominance in young adulthood, then declined in older people. Sex also influenced bacterial-age associations, with correlations being stronger in men.

The study's most striking finding was a four-marker predictive model — combining the fungus Lactarius with bacteria Chryseobacterium, Gordonia, and Psychrobacter — that classified individuals into age groups with an AUC of 0.97, indicating near-excellent discriminative accuracy.

These results underscore that fungi are a critical but overlooked dimension of skin aging biology. The model's high accuracy hints at real clinical utility for biological age estimation, though the small pilot sample and single-population design require cautious interpretation before any broader application.