Abstract

Background: The axillary microbiome is a major contributor to body malodor generation through bacterial metabolism of apocrine and eccrine secretions. Dysbiosis of this microbial community, particularly through overgrowth of odorigenic species such as Staphylococcus aureus, is associated with increased volatile compound production and local skin inflammation. Heat-treated postbiotics represent a promising class of cosmetic ingredients combining microbiological safety with retained bioactive properties. Objective: We aimed to evaluate the in vitro safety, molecular mechanisms, antipathogen and anti-inflammatory properties of heat-treated Lacticaseibacillus rhamnosus Skinbac™ SB06, and to assess the antiperspirant and deodorant efficacy of a deodorant spray formulation containing 1% SB06 in a controlled clinical study. Methods: In vitro studies assessed cytotoxicity (MTT/LDH assays), Aquaporin-3 (AQP3) expression, reactive oxygen species (ROS) production, antipathogen activity against Staphylococcus aureus (AlamarBlue assay), cytokine modulation (TNF-α, IL-6, IL-8, IL-23) in Normal Human Epidermal Keratinocytes (NHEK) and Peripheral Blood Mononuclear Cells (PBMCs), and axillary microbiome compatibility against Corynebacterium striatum, Staphylococcus epidermidis, and Staphylococcus hominis by viable plate count (CFU/mL). Clinically, a randomized split-body study (n = 20) evaluated antiperspirant effectiveness by gravimetric sweat collection and deodorant efficacy by expert olfactory panel (Likert 1–5) at 24 and 48 h. Results: In vitro testing confirmed the safety of SB06 (MTT and LDH, both non-significant vs. control). SB06 significantly increased AQP3 expression (+20%, p < 0.001) and significantly reduced ROS production (−48%, p < 0.05). Antipathogen testing showed significant reduction in S. aureus planktonic viability (−7%, p < 0.05). Microbiome compatibility testing on selected axillary-associated strains showed a differential compatibility profile, with the strongest inhibitory effect observed for C. striatum (13% residual viability at T24h, corresponding to 87% inhibition), near-complete preservation of S. epidermidis (92% residual viability at T48h), and a mild reduction in S. hominis (−15% at T48h). Cytokine modulation showed significant IL-8 and IL-23 reduction in NHEK (both p ≤ 0.05) and immunostimulatory activity in PBMCs. Clinically, SB06 reduced sweat production vs. placebo by −21.8% at T24 (p = 0.0009) and −10.0% at T48 (p = 0.0495), with significantly lower odor intensity at both timepoints (median score 3 vs. 4, p < 0.0001). Conclusions: Heat-treated L. rhamnosus SB06 showed a multimodal in vitro profile including antipathogen, anti-inflammatory, antioxidant, and AQP3-upregulating activities, and was associated with statistically significant antiperspirant and deodorant effects in a randomized controlled split-body study. These findings are consistent with SB06 being a functional postbiotic ingredient with potential for deodorant and antiperspirant applications, pending confirmation in larger controlled studies.

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