Concentrated Sodium Hydroxide, Calcium Hydroxide, Magnesium Hydroxide and Potassium Hydroxide are strong irritants and corrosive to the skin, eyes, respiratory tract and gastrointestinal system if ingested. The severity of effects caused by Sodium, Magnesium and Potassium Hydroxide is a function of the concentration, the pH, the length of tissue contact time, and local conditions and skin type.

The Joint FAO/WHO Expert Committee on Food Additives has not limited the Acceptable Daily Intake of Sodium Hydroxide, Magnesium Hydroxide or Potassium Hydroxide.
http://www.inchem.org/documents/jecfa/jeceval/jec_2154.htm
http://www.inchem.org/documents/jecfa/jeceval/jec_1302.htm
http://www.inchem.org/documents/jecfa/jeceval/jec_1982.htm

Link to FDA Code of Federal Regulations for Sodium Hydroxide
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRS...

Magnesium Hydroxide
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRS...
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRS...

Potassium Hydroxide
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRS...
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRS...

Potassium and Sodium Hydroxide
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRS...

Sodium, Calcium, Magnesium and Potassium Hydroxide
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRS...

Sodium Hydroxide and Potassium Hydroxide are listed in the Cosmetics Directive of the European Union (see Annex III) and may be used at the following concentrations and pH values: 5% by weight in nail cuticle solvents, 2% by weight in hair straighteners for general use, 4.5% by weight in hair straighteners for professional use, up to a pH 12.7 in depilatories, and up to pH 11 in other uses as a pH adjuster. The nail cuticle solvents and the general use hair straighteners containing these ingredients must be labeled "contains alkali, avoid contact with eyes, can cause blindness, keep out of reach of children." The professional hair straighters must be labeled "for professional use only, avoid contact with eyes, can cause blindness." Depilatories containing these ingredients must include the following on the label: "Keep out of reach of children, avoid contact with eyes."

Calcium Hydroxide may be used at a maximum of 7% in hair straighteners that also contain a guanidine salt. It is also permited in depilatories as a pH adjuster if the pH does not exceed 12.7, and in other products if the pH does not exceed 11. Hair straighteners and depilatory products containing this ingredient must be labeled "Contains alkali, avoid contact with eyes, keep out of reach of children", hair straighteners must also be labeled "can cause blindness" (see Annex III).

Magnesium Hydroxide may be used in cosmetics and personal care products marketed in the Europe according to the general provisions of the Cosmetics Directive of the European Union.
Link to the EU Cosmetics Directive: http://ec.europa.eu/consumers/sectors/cosmetics/documents/di...

Sodium Hydroxide, Calcium Hydroxide, Magnesium Hydroxide and Potassium Hydroxide are inorganic bases. Inorganic bases are alkalies which contain no carbon atoms. When placed in water, Sodium, Calcium, Magnesium and Potassium Hydroxide separate into cations (positively charged sodium, calcium, magnesium or potassium) and hydroxide anions (negatively charged). The hydroxide anions serve to decrease the acidity of water (increase pH).

In cosmetics and personal care products, Sodium Hydroxide, Calcium Hydroxide, Magnesium Hydroxide and Potassium Hydroxide function as a pH adjusters. Magnesium Hydroxide also functions as an absorbant.