Sodium hydroxide, also known as caustic soda is an inorganic compound with formula Na OH.
It is a white solid ionic compound consisting of sodium cations Na and hydroxide anions OH.

Sodium hydroxide is a highly caustic base that decomposes proteins at ordinary ambient temperatures and may cause severe chemical burns. It is highly soluble in water and readily absorbs moisture and carbon dioxide from the air. It forms a series of hydrates Na OH and nH2O.

Sodium hydroxide is used in many industries in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 2004 was approximately 60 million tones , while demand was 51 million tones.