The scalp microbiome — dominated by Malassezia, Cutibacterium and Staphylococcus epidermidis — regulates local pH, sebum production, and the cutaneous barrier. Prebiotics (fructooligosaccharides, inulin) selectively feed beneficial bacteria; probiotic lysates (Lactobacillus ferment) act on TLR receptors of the epidermis. Hairswiss analyzes the molecular mechanisms and the limits of these actives in cosmetic formulation.