Skin disorders of different etiology, such as dermatitis, atopic dermatitis, eczema, psoriasis, wounds, burns, and others, are widely spread in the population. In severe cases, they require the topical application of drugs, such as antibiotics, steroids, and calcineurin inhibitors. With milder symptoms, which do not require acute pharmacological interventions, medications, dietary supplements, and cosmetic products of plant material origin are gaining greater popularity among professionals and patients. They are applied in various pharmaceutical forms, such as raw infusions, tinctures, creams, and ointments. Although plant-based formulations have been used by humankind since ancient times, it is often unclear what the mechanisms of the observed beneficial effects are. Recent advances in the contribution of the skin microbiota in maintaining skin homeostasis can shed new light on understanding the activity of topically applied plant-based products. Although the influence of various plants on skin-related ailments are well documented in vivo and in vitro, little is known about the interaction with the network of the skin microbial ecosystem. The review aims to summarize the hitherto scientific data on plant-based topical preparations used in Poland and Ukraine and indicate future directions of the studies respecting recent developments in understanding the etiology of skin diseases. The current knowledge on investigations of interactions of plant materials/extracts with skin microbiome was reviewed for the first time.

Ethnopharmacological relevance Comfrey root (Symphytum officinale L., Boraginaceae) has been used in folk medicine for a long time to treat different diseases. It is recommended for swellings, phlebitis , contusions, gastro-duodenal ulcers, respiratory diseases , and metrorrhagia. Currently, preparations from S. officinale are only topically used due to its wound-healing effects, and for reducing inflammation and the treatment of broken bones, tendon damage, painful joints and muscles. Although it is a widespread plant material, little is known about the interaction of externally applied preparations of comfrey with the human skin microbiome. Aim of the study: The study aims to determine the interaction between human skin microbiota and the comfrey root extracts, by monitoring the biotransformation of the constituents present in the extract and evaluating changes in the population of the skin microbiota in an ex vivo setting. Material and methods The comfrey root extract was incubated with the human skin microbiota from ten healthy donors. The UHPLC-DAD-MSⁿ analysis determined the composition of the raw extract and the microbial metabolites. Bacterial genomic DNA was extracted and examined by amplification sequencing of the 16S rDNA to determine changes in the bacterial composition. Results: The hydroethanolic extract of comfrey root primarily consists of phenolic acids, pyrrolizidine alkaloids , and their derivatives, and lignans. The natural products present in the extract underwent biodegradation by the skin microbiota, leading to the formation of smaller molecules. It was observed that the skin microbial metabolism primarily focused on modifying the derivatives of pyrrolizidine alkaloids. It resulted in the production of deacetylated and deesterificated compounds. However, it did not lead to the conversion of these compounds into free alkaloids. Conclusions: The microbiota-triggered biotransformation of the comfrey root extract was observed. A few N-oxides were metabolized to deacetylated and deesterificated forms in ex vivo conditions. It suggests that the intermittent external applications of comfrey preparations perchance are unlikely to pose a substantial risk. While it even may serve as a potential factor influencing the extract activity in treating skin diseases.

The skin represents a complex ecosystem where host cells and microbiota coexist in dynamic equilibrium. Disruption of this balance contributes to inflammation and diseases, while natural compounds may help restore it. For centuries, marigold and chamomile have been among the most valued medicinal plants in traditional herbal medicine, widely used for treating wounds, skin inflammation, and irritations. Their long-standing therapeutic reputation is supported by rich phytochemical profiles – triterpenoids, flavonoids, phenolic acids in marigold, and sesquiterpene lactones, flavonoids, and coumarins in chamomile – known to exert anti-inflammatory, antioxidant, and soothing effects. In this study, Calendula officinalis and Matricaria recutita flower extracts’ effects were investigated on human skin microbiota and dermal cells. Both extracts remained chemically stable under microbial exposure and did not generate new metabolites, highlighting resistance to microbial metabolism. Neither extract disrupted community structure; instead, they selectively modulated microbial taxa, decreasing potentially pro-inflammatory families (Staphylococcaceae, Corynebacteriaceae, and Enterococcaceae) and enriching the Bacillales and Bacillaceae families. On the cellular level, at ≤250 µg/mL, both extracts were biocompatible with fibroblasts and keratinocytes. Marigold flower extract showed no significant anti-inflammatory effect in keratinocytes, as IL-6 and IL-8 secretion remained comparable to the stimulated control. In contrast, Chamomile flower extract markedly reduced IL-6 levels in a dose-dependent manner, with moderate effects on IL-8. In fibroblasts, both extracts had strong suppression of IL-6 and IL-8 at higher concentrations. These findings reveal a dual mechanism – direct cellular modulation and indirect microbiota-mediated rebalancing-supporting the traditional therapeutic efficacy of C. officinalis and M. recutita in skin health.