The Human Skin Microbiome Remains Unchanged After 24 Hours of Sunscreen Application

To ensure safe, long-term use, topical products should be investigated to understand how they interact with the resident skin microbiota, to mitigate potential risk. Sunscreens are essential for protecting skin from UV damage, but their effects on skin-resident microbes have not been well characterised. We examined the impact of two sunscreen formulations on both cultured skin bacteria and the skin microbiomes of human volunteers. No loss of viability was observed after a two-hour exposure to either sunscreen in cultures of Staphylococcus epidermidis, Staphylococcus capitis, Staphylococcus hominis, Micrococcus luteus and Corynebacterium tuberculostearicum. The effects of the sunscreens were then studied across the skin microbiomes of 20 human participants. Skin swabs were collected before application and at 1, 6, and 24 hours afterward. DNA was extracted and sequenced at the 16S rRNA V4 region, and sequences were denoised and taxonomically assigned using the nf-core/ampliseq pipeline. Across all time points, alpha diversity (Shannon index, Friedman’s test) and beta diversity (PERMANOVA) remained stable, with no significant differences in beta dispersion. Differential abundance analysis revealed minor fluctuations in some low abundance genera, identified as likely transient due to their low prevalence, but overall resident community composition was not significantly altered. These findings suggest that short-term sunscreen application does not disrupt the skin microbiome, supporting their safe use from a microbial standpoint. Outcomes from both in vitro and in vivo experimentation point to the compositional resilience of the skin microbiota to sunscreens.