Magnesium hydroxide in water (milk of magnesia) are used as an antacid to neutralize stomach acid, and a laxative.
Magnesium hydroxide is also used as a non-antiperspirant armpit deodorant.
According to MedlinePlus Medical Encyclopedia, milk of magnesia is useful against canker sores (aphthous ulcer) when used topically.
Milk of magnesia is also used as a folk remedy, applied and massaged in (a few minutes before washing), to relieve symptoms of seborrhea and dandruff.
An additional folk use is for the treatment of acne or oily skin by applying topically, allowing to dry, and washing it back off of the face.
It is also said to be used for seborrheic dermatitis, which is a drying and flaking of the skin similar to dandruff but often occurring on the face.
Magnesium hydroxide powder is used industrially as a non-hazardous alkali to neutralise acidic wastewaters.
Solid magnesium hydroxide has also smoke suppressing and fire retarding properties