Magnesium hydroxide is generally safe for skin when used in properly formulated cosmetic products. The Cosmetic Ingredient Review Expert Panel, the independent body that evaluates ingredient safety for the cosmetics industry, concluded that magnesium hydroxide is safe for use in cosmetics when products are formulated to be nonirritating. In lab and animal testing, magnesium hydroxide was not found to be irritating or corrosive. But the details matter, especially if you’re thinking about applying straight milk of magnesia to your face as a DIY skincare hack.
What the Safety Review Found
The Expert Panel’s formal conclusion splits magnesium hydroxide into two use categories. For products like hair straighteners and depilatories, where magnesium hydroxide acts as a pH adjuster at higher concentrations, it’s considered safe under recommended use, but the panel specifically notes that users should minimize skin contact. For all other cosmetic uses (think lotions, primers, foundations), it’s considered safe at the concentrations currently used in the industry, provided the final product is formulated to be nonirritating.
In safety testing, magnesium hydroxide did not cause irritation or corrosion in lab-based skin models, and it was not irritating in animal studies. One notable finding: at concentrations up to 50% in a carrier solution, magnesium hydroxide did trigger a sensitization response in a lymph node assay, which is a screening test for allergic potential. That’s a high concentration you wouldn’t encounter in a finished product, but it’s worth knowing if you’re considering applying undiluted or highly concentrated forms directly to your skin.
The pH Problem
Magnesium hydroxide has a pH around 10, which is solidly alkaline. Your skin’s natural acid mantle sits between pH 4.5 and 5.5, and that slightly acidic environment is critical for maintaining your skin barrier and keeping the right balance of bacteria on your skin. When the skin surface becomes too alkaline, it increases water loss through the skin and can allow harmful bacteria like Staphylococcus aureus to gain a foothold while depleting beneficial species like Staphylococcus epidermidis.
This doesn’t mean a brief application will wreck your skin. Cosmetic formulations buffer the pH so the final product isn’t as alkaline as pure magnesium hydroxide. But if you’re applying pharmacy-grade milk of magnesia straight from the bottle, you’re putting a pH 10 substance directly on your face, which can disrupt your skin’s protective acid layer over time.
Using It for Oily Skin or Acne
Magnesium hydroxide can absorb lipids, which is why some people swear by milk of magnesia as a mattifying primer. It does pull oil off the surface of your skin and reduce shine temporarily. This trick has roots in theatrical makeup, where performers used it to manage heavy, oil-based products under hot stage lights.
What it does not do is reduce oil production. Your sebaceous glands keep producing sebum at the same rate regardless of what’s sitting on the surface. So while your face may look less shiny for a few hours, the underlying oiliness isn’t changing. The evidence for acne treatment is even thinner. A single dermatologist published a letter in 1975 reporting positive outcomes using topical milk of magnesia alongside an oral antibiotic, but no study has replicated those results. Since the antibiotic alone is a standard acne treatment, there’s no way to know whether the magnesium hydroxide contributed anything.
Barrier Creams With Magnesium Compounds
Some formulated barrier creams combine magnesium hydroxide with aluminum hydroxide and stearate to create a protective layer for damaged or irritated skin. These products have been evaluated for managing eczema, allergic contact dermatitis, and irritant contact dermatitis. In cumulative irritation testing on healthy adults over 21 days, one such cream rated as mild, scoring lower than the negative control under semi-occlusive patches. Under fully occlusive conditions (tightly sealed against the skin, which is a more aggressive test), the cream was still classified as “probably mild.”
This is a different situation from applying raw milk of magnesia. These creams are specifically engineered to balance the alkalinity of the magnesium hydroxide with other ingredients, resulting in a product gentle enough for already-compromised skin. The formulation work makes all the difference.
What Happens With Repeated Use
Research on topical magnesium application to skin offers some insight into what repeated exposure looks like. In one study, researchers applied magnesium salt solutions to volunteers’ forearms at 24-hour intervals over 96 hours and measured changes in skin hydration, water loss, and pH. A concentrated magnesium solution nearly doubled skin hydration at the six-hour mark compared to baseline, though hydration returned to normal within 24 hours. No changes to skin pH were observed. However, magnesium treatment also didn’t help restore the skin barrier after it was experimentally disrupted by tape stripping, suggesting it doesn’t actively repair barrier function.
This research used magnesium chloride rather than magnesium hydroxide, so the results aren’t perfectly transferable. But the general picture is consistent with what you’d expect: magnesium compounds can temporarily affect skin hydration without meaningfully improving or worsening barrier integrity in the short term. The bigger concern with magnesium hydroxide specifically is cumulative alkaline exposure rather than the magnesium itself.
Practical Considerations
If you’re using a commercial skincare product that lists magnesium hydroxide as an ingredient, you can feel confident it’s been formulated within safe parameters. These products typically use it as a pH adjuster in small amounts, and the finished formula is balanced to be skin-compatible.
If you’re considering applying milk of magnesia directly to your skin as a primer or oil-control treatment, the risks are low for occasional use on intact skin, but daily application raises concerns. A pH of 10 applied regularly can weaken your acid mantle, increase moisture loss, and shift the bacterial balance on your skin in an unfavorable direction. People with sensitive skin, rosacea, eczema, or a compromised skin barrier are more vulnerable to these effects. For occasional use on oily skin before an event, it’s unlikely to cause problems. As a daily skincare step, there are better options specifically formulated to manage oil without disrupting your skin’s pH.