What Is Magnesium Hydroxide?
Magnesium hydroxide is a mineral‐based compound that occurs naturally as the ore brucite and can also be produced by reacting magnesium salts with alkaline water. Chemically it consists of magnesium ions bound to hydroxide ions, forming a white, odorless powder that is only slightly soluble in water. The beauty industry first noticed this ingredient in the early twentieth century when its oil-absorbing quality made it useful in face powders and early cream formulas. Today manufacturers obtain cosmetic-grade magnesium hydroxide by mixing magnesium chloride or sulfate solutions with sodium hydroxide, then filtering, washing and drying the resulting precipitate to a fine, high-purity powder.
You will most often see magnesium hydroxide in mattifying primers, setting powders, clay masks, deodorants, foundations and some liquid or cream products designed for oily or acne-prone skin. It can also appear in certain color cosmetics where it controls pH and keeps pigments from shifting.
Magnesium Hydroxide’s Cosmetic Benefits/Uses
In topical products magnesium hydroxide contributes in the following ways:
- Absorbent It soaks up excess sebum and sweat helping formulas leave a matte finish, improving wear time and reducing visible shine on the skin
- Buffering It stabilizes the pH of a product so the final formula feels gentle, stays effective and remains compatible with other active ingredients
Who Can Use Magnesium Hydroxide
Thanks to its oil absorbing nature magnesium hydroxide is most helpful for people with oily or combination skin as it cuts down shine and helps makeup last longer. Normal skin can also benefit in humid conditions. Those with very dry or sensitized skin may find it too drying because it can pull natural moisture from the surface and its mildly alkaline pH may disturb an already fragile skin barrier.
The ingredient is mineral based and typically produced without animal by-products so it is considered suitable for vegans and vegetarians. Always check the full product label in case other non-vegan ingredients have been added.
Current research shows no specific concerns for pregnant or breastfeeding women when magnesium hydroxide is used topically in cosmetic amounts. This is not medical advice and anyone who is pregnant or nursing should review any skincare product with a qualified healthcare provider to be safe.
Magnesium hydroxide does not make skin more sensitive to sunlight so it is not regarded as a photosensitizer. It can however reduce the effectiveness of strongly acidic actives if they are layered immediately after each other so allow some time between applications.
Potential Side Effects/Adverse Reactions
Reactions to topical magnesium hydroxide differ from person to person. The points below list potential side effects that could occur though most users will not experience them when the ingredient is correctly formulated.
- Dryness or tightness
- Temporary redness or mild stinging on very sensitive skin
- Disruption of the skin’s acid mantle when used in high concentration leading to flakiness or irritation
- Reduced efficacy of acidic actives applied at the same time due to its buffering action
If you notice any persistent discomfort stop using the product and consult a dermatologist or healthcare professional
Comedogenic Rating
Rating: 0 (non-comedogenic)
Magnesium hydroxide is an inert mineral that sits on the surface of the skin and does not dissolve in oils so it is very unlikely to clog pores. Its primary role is to absorb oil rather than contribute to it which keeps pores clearer instead of blocking them.
Because of this low rating it is generally considered suitable for acne-prone or breakout-prone skin types.
One extra point to keep in mind is that heavy, occlusive ingredients used alongside magnesium hydroxide in a formula could still cause congestion so always look at the product as a whole.
Summary
Magnesium hydroxide acts mainly as an absorbent and a buffering agent. It mops up excess oil and sweat leaving a matte finish and keeps a product’s pH in a skin-friendly range so other actives stay stable and gentle.
The ingredient has never reached superstar status like hyaluronic acid or niacinamide but it keeps showing up in mattifying primers, setting powders and natural deodorants because it simply does its job well.
Topically applied magnesium hydroxide is considered safe for the vast majority of users with only minor risks of dryness or mild irritation in sensitive skin. As with any new cosmetic it is wise to perform a quick patch test to make sure your skin agrees with the formula before using it on a larger area.