Longitudinal analysis of the skin microbiome in association with hand eczema, hand hygiene practices and moisturizer use.

Background: The skin microbiota maintains a physical and immunological barrier to the environment. Little is known about how the microbiome changes over time or the effect of hand hygiene practices and moisturizer use. Objectives: To assess sex‐specific changes in skin bacteria over time, and how the microbiome is related to self‐reported hand eczema, hand hygiene practices and use of moisturizers. Methods: Swab samples from the dorsal hand were collected at baseline and 6.5 years later during the COVID‐19 pandemic, in 168 participants from the RHINESSA study in Bergen, Norway. The skin samples were analysed by 16S rRNA amplicon sequencing. Results: The alpha diversity of the hand microbiome increased from baseline to follow‐up, and beta diversity differed by sex at both time points. The relative abundance increased for several bacteria from baseline to follow‐up, with sex‐specific differences. Current hand eczema and aggravating hand eczema during the COVID‐19 pandemic were associated with an increase in Staphylococcus. High hand washing frequency at home was associated with lower alpha diversity and with higher abundance of Staphylococcus, Corynebacterium, Finegoldia, and Pseudomonas and lower abundance of Propionibacterium and Pelomonas. The alpha diversity increased with increasing time passing between hand washing and sampling, whereas more frequent moisturizer use was associated with significantly lower alpha diversity, and a change in abundance for some bacteria, such as more Pseudomonas. Conclusions: This longitudinal study revealed an overall increase in skin microbial diversity over a 6‐year period, which was unexpected since follow‐up was performed during the COVID‐19 pandemic when vigorous hand hygienic practices were introduced. Sex‐specific differences were identified at both time points. Individuals with hand eczema seem to develop a more dysbiotic skin bacterial community over time. Hand washing and use of moisturizers, with typically gender‐specific habitual patterns, may lead to change in bacterial composition. [ABSTRACT FROM AUTHOR]