Magnesium Hydroxide:
The Gentle Mineral for Natural
Deodorant & Skincare
Milk of magnesia reimagined for modern cosmetics — aluminium-free odour control, oil-absorbing masks, sensitive skin soothing, and oral care. A 200-year-old mineral with a very modern application.
Magnesium hydroxide — Mg(OH)₂, better known as milk of magnesia — has been a trusted ingredient in medicine and wellness for over two centuries. Today it's experiencing a significant resurgence as one of the most effective and gentle natural alternatives to aluminium-based antiperspirants. As Australian consumers increasingly scrutinise what they apply to their underarms, magnesium hydroxide has emerged as the science-backed answer to a very common question: can natural deodorant actually work?
What Is Magnesium Hydroxide?
Magnesium hydroxide is a white, odourless, slightly soluble inorganic compound formed from magnesium and hydroxide ions. It occurs naturally as the mineral brucite, and is also commercially produced from seawater — making it a truly mineral-origin ingredient with exceptional purity credentials.
Cosmetic-grade magnesium hydroxide — ultra-fine white powder, odourless, and non-irritatingBody odour is not caused by sweat itself — sweat is largely odourless. The smell is produced when bacteria on the skin metabolise fatty acids and proteins in sweat, releasing volatile acidic compounds (including butyric and propionic acids). Magnesium hydroxide interrupts this process chemically: Mg(OH)₂ + 2H⁺ → Mg²⁺ + 2H₂O — it neutralises the acidic metabolites while simultaneously creating a mildly alkaline skin pH environment that is inhospitable to the odour-causing bacteria themselves. This is fundamentally different from aluminium-based antiperspirants, which block sweat glands entirely.
Magnesium Hydroxide vs Aluminium — The Honest Comparison
The debate around aluminium in antiperspirants has grown substantially among Australian consumers. Here's a factual, science-grounded comparison of the two approaches.
- Blocks sweat glands via aluminium salt plugs
- Stops both sweat and odour
- Ongoing research into aluminium absorption
- Can cause irritation, contact dermatitis
- Stains fabric yellow (aluminium + sweat)
- Not suitable for broken or recently shaved skin
- Neutralises odour at the bacterial level
- Allows natural sweating — no pore blocking
- Zero absorption concern — not bioavailable in this form
- Gentle on sensitive and recently shaved skin
- No fabric staining
- Safe for pregnancy and post-mastectomy use
| Property | Baking Soda (bicarb) | Magnesium Hydroxide |
|---|---|---|
| pH | ~8.3 | ~10 (more effective against bacteria) |
| Skin irritation | Common — causes rash in many users | Rare — gentle on sensitive skin |
| Texture in formulas | Gritty, can feel scratchy | Ultra-fine, smooth, non-gritty |
| Deodorising mechanism | Acid neutralisation | Acid neutralisation + antibacterial environment |
| Suitable for underarms | Yes, but with caveats | Yes — widely tolerated |
Baking soda (sodium bicarbonate, pH ~8.3) is widely used in natural deodorants but notoriously causes contact dermatitis in a significant proportion of users — particularly after repeated application to freshly shaved skin. The irritation occurs because the skin's natural pH is around 4.5–5.5, and bicarb disrupts this balance aggressively. Magnesium hydroxide operates at a higher pH (~10) but paradoxically causes far less irritation because it is only sparingly soluble in water — meaning it doesn't fully ionise on skin contact. Instead it acts as a buffered, sustained-release pH modifier, which is far gentler than the rapid alkaline shift from bicarb.
What Else Can It Do?
Magnesium hydroxide's usefulness extends well beyond deodorant. Its unique combination of mineral purity, gentle alkalinity, and fine particle structure makes it valuable across several cosmetic categories.
Cosmetic Applications & Usage Rates
🢐 Natural Deodorant Cream/Stick 5–15%
The primary cosmetic application. Combine with shea butter, coconut oil, and arrowroot for a smooth, effective underarm cream. Outperforms bicarb for sensitive skin. Can be enhanced with zinc ricinoleate for additional odour-locking action.
🏒 Face Masks & Cleansers 10–30%
Used as a gentler alternative to kaolin clay. Absorbs excess sebum without over-drying. Blend with French green clay, aloe vera gel, and a hydrosol. Particularly effective for oily, acne-prone, and sensitive combination skin.
🧋 Natural Toothpaste 5–10%
Functions as a pH buffer (neutralises mouth acid that causes enamel erosion), mild abrasive for whitening, and antibacterial agent. Combine with coconut oil, xylitol, bentonite clay, and peppermint essential oil for a complete natural toothpaste.
🫕 Soaps & Body Washes 1–3%
Small additions contribute mild pH buffering, gentle cleansing action, and a skin-soothing effect. Particularly useful in shaving soaps and post-shave balms where skin is sensitised and reactive.
🌞 Setting Powder & Dry Shampoo 10–20%
Ultra-fine grade works as a natural oil-absorbing setting powder in cosmetics. Blends seamlessly with arrowroot, rice starch, and mica for a dry, weightless finish. Also effective in dry shampoo formulations for sebum absorption.
💐 Eczema & Sensitive Skin Balms 2–5%
Low concentrations in emollient balms help neutralise irritating acid metabolites on inflamed skin while providing a calming mineral buffer. Pair with colloidal oat, zinc oxide, and calendula-infused oil for a complete barrier-support balm.
Magnesium hydroxide integrates into a wide range of cosmetic formats — from powder masks to cream deodorantsDIY Magnesium Hydroxide Deodorant Cream
This gentle, effective underarm cream is suitable for sensitive skin and those who have reacted to bicarb-based deodorants. No aluminium, no bicarb, no synthetic fragrance.
Magnesium Deodorant Cream
Yield: ~110 g (1 standard tin) · Shelf life: 6–12 months · Suitable for sensitive skin
- 30 g magnesium hydroxide powder
- 40 g refined shea butter
- 20 g coconut oil (refined)
- 10 g arrowroot powder
- 10 drops lavender essential oil
- Optional: 5 drops tea tree EO
- Double boiler or heatproof bowl
- Silicone spatula
- Small whisk or stick blender
- Sterilised tin or glass jar (120 mL)
- Digital scale (0.1 g accuracy)
- Sterilise your tin with isopropyl alcohol. Allow to dry completely.
- Gently melt shea butter and coconut oil together in a double boiler over low heat. Do not overheat — remove from heat as soon as melted.
- Allow to cool to approximately 40°C (warm to touch, not hot).
- Whisk in magnesium hydroxide and arrowroot powder in three additions, whisking well between each to prevent lumps.
- Add essential oils and stir thoroughly to distribute.
- Pour or spoon into your sterilised tin. Allow to set at room temperature (2–3 hours) or refrigerate for 30 minutes.
- Cap and label with the date.
Other Uses & What to Look for When Buying
Magnesium hydroxide's versatility extends beyond personal care. Understanding its full application range helps formulators appreciate why grade and particle size matter when choosing a supplier.
💊 Pharmaceutical antacid Oral use
The original "milk of magnesia" use — neutralises excess stomach acid for heartburn and indigestion relief. The same acid-neutralising chemistry that works in deodorant works in the gut. Requires pharmaceutical-grade material for oral consumption.
💉 Gentle laxative Oral use
Acts osmotically — draws water into the bowel, softening stool. Standard treatment for occasional constipation. Again requires pharmaceutical grade for internal use; cosmetic grade is for topical application only.
🔥 Flame retardant Industrial
When heated, releases water molecules, absorbing heat and suppressing combustion. Used in polymer compounds and building materials. Demonstrates the thermal stability that also makes it safe in slightly-heated cosmetic formulations.
🌿 Water treatment Industrial
Neutralises acidic industrial wastewater before discharge. The same buffering capacity that makes it useful in oral care helps industrial processes maintain safe pH levels without harsh chemicals.
Not all magnesium hydroxide is the same. For cosmetic use, specify cosmetic or USP grade (not industrial), with a particle size of <10 microns (ultra-fine) for smooth skin feel — coarser grades feel chalky and don't disperse well in creams. Check that the supplier provides a Certificate of Analysis (CoA) confirming heavy metal limits (especially lead and arsenic), microbial testing, and assay purity (>95% Mg(OH)₂). Soapmaid's magnesium hydroxide meets cosmetic-grade specifications and is available with a CoA on request.
Shop Cosmetic-Grade Magnesium Hydroxide
Ultra-fine powder · Deodorant & skincare grade · Australian stock
Click & Collect at Springvale South · Fast Australia-wide shipping · Bulk available