Magnesium hydroxide is an inorganic base valued in cosmetics for two core performance attributes: acid neutralization (pH buffering) and lipid/aqueous absorption. In skincare, dispersed Mg(OH)₂ particles bind and mop up surface sebum while moderating the microenvironmental pH of a formula or deposition film. That combination makes it a workhorse for mattifying primers, oil-control lotions, masks, and body/foot powders, where it reduces shine without the draggy feel associated with higher-load clays. Because Mg(OH)₂ is only sparingly soluble, it tends to act as a reservoir buffer, neutralizing acidic odorants or by-products as they appear, while contributing to consistent rheology and opacity in emulsions.
In hair-care and scalp-care, magnesium hydroxide can be leveraged indirectly: as a formulation buffer and absorbent in dry shampoos, scalp powders, and rinse-off cleansers designed for oily scalps. It aids sebum pick-up on hair fibers and scalp, supports fragrance longevity by limiting malodor acids on the skin’s surface, and stabilizes pH-sensitive systems during manufacturing.
Quick Insights
Ingredient Rating:
GOOD
Type of Ingredient:
Texture Enhancer, Cleansing Agent, Astringent, Microbiome Balance Agent, Barrier Support, Oil Control Agent, Solvent and Preservative
Intended Function:
Neutralize acidic odorants and buffer formula/skin-surface pH while absorbing excess sebum and moisture.
Common Applications:
Aluminum-free deodorants, cream/solid deodorants, talc-free body & foot powders, mattifying primers, clay masks, and oily-skin lotions.
Target Audience:
Brands building gentle, aluminum-free odor control and oil-control systems for sensitive, combination, or oily skin types.
Also Known As:
Milk of Magnesia, Brucite (mineral form), Mg(OH)₂.
Safety Analysis
Regulatory & use profile: Magnesium hydroxide is listed for cosmetic use with recognized functions of pH adjustment and absorbency. It is widely used across categories (bath, cleansing, hair color, skin care, deodorant) under general cosmetic regulations without special concentration limits, provided products are formulated to be non-irritating.
Toxicology: Safety assessments of inorganic hydroxides conclude cosmetic uses are safe when formulated to appropriate pH and with standard precautions. Mg(OH)₂ shows low dermal irritation and sensitization potential relative to stronger, more soluble alkalis. Its poor solubility limits ion release, moderating causticity in finished products.
Irritation risk management: As an alkaline base, over-neutralization or excessive in-use pH (e.g., ≥10) can disrupt the acid mantle and increase irritation potential, especially in compromised skin or with high-friction underarm use. Deodorant systems should buffer to skin-compatible pH targets and avoid unnecessary co-alkalizers.
Not a UV filter: Mg(OH)₂ does not function as an approved sunscreen active; any opacity it imparts is aesthetic, not a tested photoprotective claim.
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