Background: Magnesium hydroxide has attracted interest as an ingredient in aluminum-free axillary deodorants because of its alkaline properties, availability, and potential effects on odor-associated microorganisms. In addition to purpose-designed cosmetic formulations, commercially available oral magnesium hydroxide suspensions, commonly known as milk of magnesia, are reportedly applied directly to the axillae for odor control. However, the experimental evidence supporting these applications remains fragmented, and laboratory antimicrobial findings have not been adequately distinguished from clinically demonstrated deodorant efficacy.
Objective: To critically map experimental evidence concerning magnesium hydroxide-containing deodorants, evaluate microbiological and physicochemical findings, and examine the scientific rationale and evidence gaps associated with the topical repurposing of oral milk of magnesia.
Methods: An exploratory evidence-mapping review was conducted using five full-text experimental investigations from Brazil, Malaysia, and India, supplemented by relevant scientific and documentary literature. Studies were classified according to whether magnesium hydroxide was directly investigated or whether they provided indirect methodological evidence concerning alternative deodorants. Formulation composition, antimicrobial outcomes, physicochemical characteristics, clinical measurements, and methodological limitations were narratively synthesized.
Results: Three studies directly investigated magnesium hydroxide-containing formulations, whereas two evaluated alternative deodorants without magnesium hydroxide. A Brazilian study reported a 7-mm bacterial inhibition zone for a multicomponent magnesium hydroxide deodorant, compared with 15 mm for a vancomycin control. Another Brazilian investigation demonstrated formulation feasibility, with a final pH of approximately 6.0, but did not establish clinical odor reduction. A Malaysian study reported weaker antibacterial activity for magnesium hydroxide than for the essential oils tested. An Indian investigation involving nine participants demonstrated a 65.0% reduction in mean axillary bacterial counts after four hours, although its formulation did not contain isolated magnesium hydroxide. None of the five studies established the clinical efficacy or long-term dermatological safety of oral milk of magnesia applied to the axillae.
Conclusions: Magnesium hydroxide is a feasible ingredient for experimental deodorant formulations, but its independent clinical effectiveness remains unproven. The topical repurposing of oral milk of magnesia represents a relevant, insufficiently investigated practice. Controlled clinical studies are required to establish odor reduction, duration of action, comparative efficacy, microbiological effects, and repeated-use safety.