What Is Aluminum/Magnesium Hydroxide Stearate?
Aluminum/Magnesium Hydroxide Stearate is a compound created when aluminum hydroxide and magnesium hydroxide react with stearic acid, the fatty acid found in many plant and animal fats. The reaction coats the metal hydroxide particles with stearate, turning them into a fine, white powder that easily blends into creams, lotions and makeup.
Chemists started using this ingredient in cosmetic labs in the 1970s when they needed a plant based way to thicken oil-in-water emulsions without leaving a greasy feel. Over time formulators noticed that the powder also helped keep pigments from separating, so it made its way into color cosmetics.
The manufacturing process is straightforward: aluminum and magnesium salts are mixed with water, converted to their hydroxide forms, then treated with purified stearic acid under heat. After thorough washing and drying the resulting powder is milled to a specific particle size so it spreads smoothly in finished products.
Today you will most often spot Aluminum/Magnesium Hydroxide Stearate in foundations, pressed and loose powders, tinted moisturizers, sunscreens, cream blushes, lipsticks, anti-aging serums, clay masks and even some hair styling creams where it helps keep oil and water phases stable.
Aluminum/Magnesium Hydroxide Stearate’s Cosmetic Benefits/Uses
This versatile ingredient supports both the structure and feel of a formula.
- Emulsion stabilising: By coating tiny oil droplets the powder keeps water and oil from separating, so creams stay smooth and uniform from the first use to the last
- Viscosity controlling: It thickens liquids just enough to give them a rich, cushiony texture without weighing them down which helps foundations resist streaking and lets lotions glide on evenly
Who Can Use Aluminum/Magnesium Hydroxide Stearate
This ingredient works for most skin types. Its light powder texture helps control excess oil without drying so oily and combination skin can enjoy a smoother finish. Dry and normal skin benefit from the creamy slip it gives lotions and makeup. Even sensitive skin usually tolerates it because the particles sit on the surface instead of soaking in, though anyone with a known allergy to aluminum compounds should steer clear.
The stearic acid used today is almost always sourced from plants like coconut or palm, not animal fat, making products that use it suitable for vegans and vegetarians. If you avoid animal-derived ingredients for personal or religious reasons, check the brand’s sourcing statement to be sure.
Formulators consider Aluminum/Magnesium Hydroxide Stearate a low-risk choice during pregnancy and breastfeeding because it stays on the outer skin layers. Still, this is not medical advice and anyone expecting or nursing should show the ingredient list to their doctor before starting a new product.
The powder does not increase photosensitivity, so it will not make skin more prone to sunburn. It also plays nicely with common actives like vitamin C, niacinamide and retinoids since it acts mainly as a stabilizer rather than a reactive ingredient.
Potential Side Effects/Adverse Reactions
Reactions to topical Aluminum/Magnesium Hydroxide Stearate differ from person to person. The following are potential side effects, but most users will not experience them when the ingredient is used correctly in a well-formulated product.
- Mild skin irritation such as redness or itching in people sensitive to aluminum compounds
- Contact dermatitis in rare cases of allergy to stearates or metal salts
- Clogged pores or breakouts if the formula contains other comedogenic ingredients and is not removed thoroughly
- Eye irritation or watering if loose powder containing the ingredient gets into the eyes
- Respiratory discomfort from inhaling large amounts of airborne powder during application
If any of these issues occur stop using the product and consult a healthcare professional.
Comedogenic Rating
Rating: 1/5—Aluminum/Magnesium Hydroxide Stearate is classed as low on the pore-clogging scale. The powder sits on the skin surface and does not melt into pores, while the stearate coating is firmly bound to the mineral core so it releases very little free fatty acid. Most people, even those prone to breakouts, can use it without seeing extra bumps.
Because the ingredient is usually blended with oils, butters or silicones, the finished product’s overall comedogenic potential depends on the full formula. Always look at the entire ingredient list if you struggle with congestion.
Summary
Aluminum/Magnesium Hydroxide Stearate thickens lotions and makeup and keeps oil and water mixed so textures stay silky and pigments do not separate. It does this by coating oil droplets and adding a gentle gel-like body to the formula.
The ingredient is fairly popular in foundations and pressed powders but you will also spot it in sunscreens and skin care creams when chemists want a light, non-greasy feel.
Current research and decades of use show it is safe for most people, with only rare reports of irritation or allergy. Still, skin can be unpredictable so it is wise to patch test any new product that lists this ingredient before applying it all over.