Sodium hydroxide is a highly corrosive base and alkali that decomposes lipids and proteins at ambient temperatures and may cause severe chemical burns.

[14] Sodium hydroxide is used in many industries: in the making of wood pulp and paper, textiles, drinking water, soaps and detergents, and as a drain cleaner.

Similar to the hydration of sulfuric acid, dissolution of solid sodium hydroxide in water is a highly exothermic reaction[17] where a large amount of heat is liberated, posing a threat to safety through the possibility of splashing.

Concentrated (50%) aqueous solutions of sodium hydroxide have a characteristic viscosity, 78 mPa·s, that is much greater than that of water (1.0 mPa·s) and near that of olive oil (85 mPa·s) at room temperature.

[16] Sodium hydroxide can form several hydrates NaOH·nH2O, which result in a complex solubility diagram that was described in detail by Spencer Umfreville Pickering in 1893.

[13] A hot water solution containing 73.1% (mass) of NaOH is a eutectic that solidifies at about 62.63 °C as an intimate mix of anhydrous and monohydrate crystals.

Such reactions are often used to "scrub" harmful acidic gases (like SO2 and H2S) produced in the burning of coal and thus prevent their release into the atmosphere.

For example, Glass reacts slowly with aqueous sodium hydroxide solutions at ambient temperatures to form soluble silicates.

Flasks and glass-lined chemical reactors are damaged by long exposure to hot sodium hydroxide, which also frosts the glass.

[24] This is due to the lower enthalpy of formation of iron(III) oxide (−824.2 kJ/mol) compared to sodium hydroxide (−500 kJ/mol) and positive entropy change of the reaction, which implies spontaneity at high temperatures (ΔST > ΔH, ΔG < 0) and non-spontaneity at low temperatures (ΔST < ΔH, ΔG > 0).

The following colours are observed: Zinc and lead salts dissolve in excess sodium hydroxide to give a clear solution of Na2ZnO2 or Na2PbO2.

In the United States, the major producer of sodium hydroxide is Olin, which has annual production around 5.7 million tonnes from sites at Freeport, Texas; Plaquemine, Louisiana; St. Gabriel, Louisiana; McIntosh, Alabama; Charleston, Tennessee; Niagara Falls, New York; and Bécancour, Canada.

Poor quality crude oil can be treated with sodium hydroxide to remove sulfurous impurities in a process known as caustic washing.

This process involved placing a carcass into a sealed chamber, then adding a mixture of sodium hydroxide and water (which breaks the chemical bonds that keep the flesh intact).

This eventually turns the body into a liquid with a dark brown color,[35][36] and the only solids that remain are bone hulls, which can be crushed between one's fingertips.

[37] Sodium hydroxide is frequently used in the process of decomposing roadkill dumped in landfills by animal disposal contractors.

If a dilute solution is spilled on the skin, burns may result if the area is not washed thoroughly and for several minutes with running water.

Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications.

Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAlO2, Na3AlO3, Na[Al(OH)4], Na2O·Al2O3 or Na2Al2O4.

This only works with anhydrous sodium hydroxide, because combined with water the fat would turn into soap, which would be tainted with methanol.

[43] Sodium hydroxide is an ingredient used in some skin care and cosmetic products, such as facial cleansers, creams, lotions, and makeup.

Surfactants can be added to the sodium hydroxide solution in order to stabilize dissolved substances and thus prevent redeposition.

Sodium hydroxide used in this manner replaced many solvent-based systems in the early 1990s[citation needed] when trichloroethane was outlawed by the Montreal Protocol.

Water and sodium hydroxide detergent-based parts washers are considered to be an environmental improvement over the solvent-based cleaning methods.

These reactions are sped by the heat generated when sodium hydroxide and the other chemical components of the cleaner dissolve in water.

The standard first aid measures for alkali spills on the skin is, as for other corrosives, irrigation with large quantities of water.

[51] Sodium hydroxide is corrosive to several metals, like aluminium which reacts with the alkali to produce flammable hydrogen gas on contact.

Sodium hydroxide is often stored in bottles for small-scale laboratory use, within intermediate bulk containers (medium volume containers) for cargo handling and transport, or within large stationary storage tanks with volumes up to 100,000 gallons for manufacturing or waste water plants with extensive NaOH use.

Common materials that are compatible with sodium hydroxide and often utilized for NaOH storage include: polyethylene (HDPE, usual, XLPE, less common), carbon steel, polyvinyl chloride (PVC), stainless steel, and fiberglass reinforced plastic (FRP, with a resistant liner).

[16] Sodium hydroxide must be stored in airtight containers to preserve its normality as it will absorb water and carbon dioxide from the atmosphere.