Sodium Hydroxide, commonly known as lye or caustic soda, is a highly versatile inorganic compound used in various industrial and cosmetic applications. It is a strong base that plays a critical role in adjusting pH levels, saponification, and as a cleaning agent. In cosmetic formulations, Sodium Hydroxide is used to neutralize acidic ingredients and to help achieve the desired consistency and stability of products.

Chemical Composition and Structure

The chemical composition of Sodium Hydroxide includes:

• Sodium (Na): An alkali metal that forms a strong ionic bond with hydroxide ions.
• Hydroxide Ion (OH⁻): A negatively charged ion that contributes to the basic properties of the compound.

Structurally, Sodium Hydroxide exists as a white crystalline solid or as a colorless liquid in its aqueous form, readily soluble in water.

Physical Properties

• Appearance: Typically a white solid in the form of flakes, granules, or pellets; in solution, it appears as a clear liquid.

• Solubility: Highly soluble in water, releasing heat during dissolution.

• pH: Strongly alkaline, with a pH typically above 13 in solution.

• Odor: Odorless.

• Stability: Stable under normal conditions; should be stored in a cool, dry place away from moisture and acids.

Production Process

• Synthesis: Sodium Hydroxide is commonly produced through the electrolysis of sodium chloride (table salt) in a process known as the chlor-alkali process, which produces chlorine gas and hydrogen gas as by-products.

• Purification: The produced sodium hydroxide is purified to remove impurities and ensure high quality.

• Formulation: Sodium Hydroxide is incorporated into various cosmetic products to adjust pH and enhance formulation stability.

It appears in the form of a white powder or white, odourless flakes.

What it is used for and where

Cosmetics

It is a restricted ingredient III/15a a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported: Potassium or sodium hydroxide

Product Type, body parts    (a) Nail cuticle solvent (b) Hair straightener (c) pH adjuster for depilatories (d) Other uses as pH adjuster Callosity softener/remover (entry 15d)

Maximum concentration in ready for use preparation    (a) 5% (b) 2% (General use) and 4.5% (Professional use) Entry 15d: 1,5%

Other    (b) 1. General use 2. Professional use (c) up to pH 12.7 (d) up to pH 11 15 d Contains alcakali, Avoid contact with eyes Keep out of reach of chindren ans Read directions for use carefully

Wording of conditions of use and warnings    (a) Contains alkali Avoid contact with eyes Can cause blindness Keep out of reach of children (b) 1. Contains alkali Avoid contact with eyes Can cause blindness Keep out of reach of children 2. For professional use only Avoid contact with eyes Can cause blindness (c) Keep out of reach of children Avoid contact with eyes

Buffering agent. It is an iingredient that can bring an alkaline or acid solution to a certain pH level and prevent it from changing, in practice a pH stabiliser that can effectively resist instability and pH change.

Denaturant. The ionic or polar molecules of this ingredient included in formulations that interact with protein groups, modulate the properties of the solution to suit specific needs.

Medical

Sodium hydroxide, like phenol, is used in the treatment of chemical matricectomy or correction of ingrown nails (1), to eliminate partially occluded vascular access ports (2), 

Safety

Sodium hydroxide is corrosive and contact with sensitive areas of the body such as around the eyes, nose and on the skin should be avoided.

Food

Ingredient listed in the European food additives list as E524, acidity regulator.

Other uses

• Alkaline reagent in lead extraction.
• Desulphurisation of crude oil.
• Cellulose pulp treatment

• Molecular Formula   NAOH
• Molecular Weight   39.997   
• CAS  1310-73-2
• UNII    55X04QC32I
• EC Number   215-185-5 

Synonyms:

• Caustic Soda
• Sodium hydrate

References_____________________________________________________________________

(1) Bostanci, S., Kocyigit, P. and Gürgey, E., 2007. Comparison of phenol and sodium hydroxide chemical matricectomies for the treatment of ingrowing toenails. Dermatologic surgery, 33(6), pp.680-685.

Abstract. Objective: Chemical matricectomy is performed mainly by two agents: phenol and sodium hydroxide. Both agents have excellent cure rates, but there are no data about the comparison of postoperative healing periods. This study was designed to compare the postoperative morbidity rates of sodium hydroxide and phenol matricectomies....Conclusion: Both sodium hydroxide and phenol are effective agents giving high success rates, but sodium hydroxide causes less postoperative morbidity and provides faster recovery.

Tatlican, S., Eren, C., Yamangokturk, B. and Eskioglu, F., 2010. Retrospective comparison of experiences with phenol and sodium hydroxide in the treatment of Ingrown nail. Dermatologic Surgery, 36(3), pp.432-434.

(2) Ter Borg, F., Timmer, J., De Kam, S.S. and Sauerwein, H.P., 1993. Use of sodium hydroxide solution to clear partially occluded vascular access ports. Journal of Parenteral and Enteral Nutrition, 17(3), pp.289-291.

Abstract. Gradual vascular access port or tunneled central venous catheter occlusion during total parenteral nutrition is a common complication of unknown etiology, usually unresponsive to treatment with urokinase, ethanol, or hydrochloric acid. After establishing safety with regard to catheter materials and efficacy in dissolving the occluding substance in vitro, we treated a total of 13 vascular access ports (10 patients) that had occluded gradually during "three-in-one" total parental nutrition by slow perfusion with 10 to 20 mL of 0.1 mmol/mL sodium hydroxide solution. We found a mean increase in flow (results are flow rates under gravity-dependent vascular access port inlet pressure of 1.5 kPa) from 37 microL/s (95% upper confidence limit, 45 microL/s) to 75 microL/s (95% lower confidence limit, 64 microL/s; p < .001). For normal use, a flow of 50 microL/s is sufficient. There were no side effects. Five vascular access ports remained in excellent function during a follow-up period of 9 months. The others had reocclusions, but the partial reocclusions could be treated successfully.