Topical Zinc Oxide Nanoparticle Formulations for Acne Vulgaris: A Systematic Review of Pre-Clinical and Early-Phase Clinical Evidence.

Abstract

<b>Background and objectives:</b> Antibiotic resistance in <i>Cutibacterium acnes</i> is undermining topical macrolides and clindamycin, prompting renewed interest in zinc oxide nanoparticles (ZnO-NPs) as non-antibiotic alternatives. We aimed to (i) determine the antimicrobial and anti-inflammatory performance of topical ZnO-NP formulations across in vitro, animal and early human models; (ii) identify physicochemical parameters that modulate potency and tolerance; and (iii) delineate translational gaps and priority design elements for randomised trials. <b>Methods:</b> We systematically searched PubMed, Scopus and Web of Science until 1 June 2025 for in vitro, animal and human studies that evaluated ≤100 nm ZnO-NPs applied topically to <i>C. acnes</i> cultures, extracting data on bacterial load, lesion counts, biophysical skin parameters and acute toxicity. Eight eligible investigations (five in vitro, two animal, one exploratory human) analysed particles 20-50 nm in diameter carrying mildly anionic zeta potentials. <b>Results:</b> Hyaluronic acid-coated ZnO-NPs achieved a sixteen-fold higher selective kill ratio over <i>Staphylococcus epidermidis</i> at 32 µg mL¹, while centrifugally spun polyvinyl alcohol dressings reduced <i>C. acnes</i> burden by 3.1 log₁₀ on porcine skin within 24 h, and plant-derived nanogels generated inhibition zones that were 11% wider than benzoyl-peroxide's 5%. In human subjects, twice-daily 0.5% hyaluronic-ZnO nanogel cut inflammatory-lesion counts by 58% at week four and lowered transepidermal water loss without erythema. Preclinical safety was reassuring, zero mortality among animals at 100 µg mL¹ and no irritation among patients, although high-dose sunscreen-grade ZnO (20 nm) delayed rat wound closure by 38%, highlighting dose-dependent differences. <b>Conclusions:</b> Collectively, the evidence indicates that nanoscale reformulation markedly augments zinc's antibacterial and anti-inflammatory performance while maintaining favourable acute tolerance, supporting progression to rigorously designed, adequately powered randomised trials that will benchmark ZnO-NPs against benzoyl peroxide and retinoids, optimise dosing for efficacy versus phototoxicity, and establish long-term dermatological safety.