Magnesium hydroxide is one of many naturally occurring salts of magnesium and is a common compound found in antacids and laxatives. You may have heard of milk of magnesia which is a mixture of magnesium hydroxide and water that has been used for years to relieve occasional heartburn due to excess stomach acid, indigestion, and constipation.
Magnesium hydroxide is used in a natural deodorant for the same reason as baking soda, it alters the pH of the skin to make it more alkaline. This higher pH results in an environment that is too alkaline for odor-causing bacteria to live happily in your armpit. This antibacterial property is what makes it effective against underarm odor. Less bacteria means less odor.
Magnesium Hydroxide vs Baking Soda (Sodium Bicarbonate)
As I mentioned above magnesium hydroxide gets its antibacterial properties from its high pH (it is actually more alkaline than baking soda). So why does magnesium hydroxide usually cause less irritation than baking soda? They differ in how they react with water (in this case sweat). Magnesium hydroxide is less water-soluble which means it takes longer to fully dissolve in the sweat. Think of it as a “slow-release” antibacterial which allows the armpit a bit more time to adjust to the increase in pH.
It is believed that since the pH of your underarm skin changes more slowly, there is less potential for irritation when compared to baking soda.
Baking soda and magnesium hydroxide are both great bacteria-fighting ingredients used in natural deodorants. In general, baking soda tends to perform better in fighting odors and absorbing wetness, while magnesium hydroxide is gentler on the skin and comes with less risk of irritation.
Although magnesium hydroxide seems to be less irritating than baking soda since it raises the pH of underarm skin, it may still cause skin irritation for those with very sensitive skin.
