From Brewing Waste to Skin Health: Microbiota-Modulating Potential of Humulus lupulus in Atopic Dermatitis

Atopic dermatitis (AD) is associated with skin microbiota dysbiosis, particularly the overgrowth of Staphylococcus aureus (SA) and Staphylococcus epidermidis (SE), which contribute to inflammation and barrier disruption. Humulus lupulus (hop) extracts contain bioactive compounds with antimicrobial potential. This study aimed to evaluate, in vitro, the antimicrobial and anti-biofilm effects of hop extract, obtained from brewing industry waste, against SA and SE strains relevant to AD. The extract was produced using a food-grade ethanolic extraction, chemically characterised, and tested for antimicrobial activity and biofilm inhibition using standard in vitro assays. The extract contained humulone, lupulone, and xanthohumol and complied with microbiological quality requirements. The MIC was 0.129% (w/v) for both strains; the MLC was 0.515% for SA and 1.030% for SE. Biofilm inhibition was significant for SA at MIC, whereas SE required 5× MIC (p < 0.05). Humulus lupulus extracts obtained from brewing waste demonstrate effective antimicrobial and anti-biofilm activity, supporting their potential as sustainable agents for modulating skin microbiota in AD management.