Sodium Hydroxide (NaOH) is a water soluble white which occur in flakes, pellets, granules and powders. Sodium Hydroxide is commonly used in the formulation of bath products, cleansing products, shampoos and shaving products. Sodium Hydroxide is also used to hydrolyze fats (as in saponification) and form soaps. It is also known as caustic soda and soda lye.

Sodium Hydroxide is created via electrolysis of sodium chloride.  Sodium Hydroxide is a strong alkaline substance that dissociates completely in water to sodium and hydroxyl ions. This creates a strong exothermic reaction when it is added to water.

Sodium Hydroxide is an inorganic base, which means it is an alkali containing no carbon atoms. Sodium Hydroxide separates into cations (positively charged sodium) and hydroxide anions (negatively charged) when added to water and the hydroxide anions decrease the acidity of the water (increasing the pH).  This is why Sodium Hydroxide is commonly used as a pH adjuster in formulas.

Concentrated Sodium Hydroxide is a strong irritant and corrosive to the skin, eyes, respiratory tract and gastrointestinal system if ingested. The severity of effects caused by Sodium Hydroxide is a function of the concentration, the pH, the length of tissue contact time and local conditions and skin type.  Protective equipment such as rubber gloves, safety clothing, face mask and eye protection should always be used when handling Sodium Hydroxide or its solutions.  Proper ventilation should always be used when handling or reacting Sodium Hydroxide.  Sodium Hydroxide should be stored in airtight containers because it readily absorbs the water in the air.

Consumers won’t come in contact with dangerous unreacted lye in cosmetics and soaps.  In the case of soap the Sodium Hydroxide is a reagent. A reagent is a substance that is used in a chemical reaction to produce other substances.  Sodium Hydroxide is used to cause a reaction called saponification to create soap. Sodium Hydroxide is completely safe after it has been combined with other constituents to create an effective, safe, and diverse cleaning agent known as soap. There isn’t un-reacted Sodium Hydroxide in the finished soap because a new product has been formed.

The FDA includes Sodium Hydroxide on its list of substances affirmed as GRAS for direct addition to food.  The Joint FAO/WHO Expert Committee on Food Additives has not limited the Acceptable Daily Intake of Sodium Hydroxide.  Sodium Hydroxide is listed in the Cosmetics Directive of the European Union (see Annex III), and may be used at the specific concentrations, pH values and warning labels when it is used in nail cuticle solvents, hair straighteners and in depilatories.  It can be up to pH 11 for other uses as a pH adjuster.

You should always have a current Material Safety Data Sheet (MSDS) on hand when using Sodium Hydroxide

Author

From the UK, Colin Sanders has been a formulator of cosmetic and topical pharmaceuticals for 27 years. Over that time he has formulated nearly every category of product including shampoos, cosmetic skin creams, pharmaceutical skin creams, face masks, lip balms and so on. Colin has been an active member of the Society of Cosmetic Scientists since 1985, and in 1999, organized the first of the Formulate shows. His degree is in environmental science, and he continues to take a keen interest in the impact of human activities on the planet. Colin regards himself as an environmental activist and all round green. When not in the lab, he writes a blog, Colin’s Beauty Pages, with the intention of entertaining and hopefully informing users of cosmetic and personal care products with some insider insights, a bit of science and his own opinions.

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