* A pH adjuster

* Considered a strong irritant

* Also known as lye, caustic soda, soda lye or sodium hydrate

Functions of Sodium Hydroxide:

Sodium Hydroxide is an inorganic compound used to control the pH levels or serve as a buffering agent in cosmetics and personal care products. It was historically used in the formulation of soaps, but is currently seen in a variety of formulas, including bath products, cleansing products, fragrances, foot powders, hair dyes and colors, makeup, nail products, personal cleanliness products, shampoos, shaving products, depilatories, skin care products, and suntan products, as well as chemical hair straighteners and hair wave sets (CosmeticsInfo.org and CosmeticsCop.com). It is also a popular ingredient in industrial solvents as a chemical base for soaps, oven cleaners, detergents and drain cleaners because of its ability to dissolve grease, oils, fats and protein based deposits, according to Wikipedia. Less frequently, Sodium Hydroxide is seen as an ingredient in toothpastes.

Sodium Hydroxide is FDA approved, and has received the GRAS (Generally Recognized as Safe) rating as a direct food additive. However, it is primarily used in the washing and chemical peeling of produce. It is approved for use in cosmetics and personal care products in varying concentrations: 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.

Safety Measures/Side Effects of Sodium Hydroxide:

Sodium Hydroxide is considered a moderate hazard ingredient by the Cosmetics Database, which notes concerns regarding cancer, and moderate concerns regarding neurotoxicty, organ system toxicity and irritation. It is classified as "expected to be toxic or harmful" and one or more animal studies show brain and nervous system, metabolic, and sense organ effects at very low doses and there are warnings regarding using this ingredient around the eyes or mouth.

Although Sodium Hydroxide has been linked to cancer, specifically of the esophagus, the CDC found that these cases were after 15 - 40 years of exposure, and were caused by corrosion induced by Sodium Hydroxide and "were most likely the result of tissue destruction and scar formation rather than a direct carcinogenic action of sodium hydroxide itself."

Sodium Hydroxide is, however, a known irritant. Studies by the National Institute for Occupation Safety and Health found that this ingredient causes "Irritation eyes, skin, mucous membrane; pneumonitis; eye, skin burns; temporary loss of hair" and recommends that consumers prevent skin and eye contact. The CDC reports that "Skin contact with sodium hydroxide can cause severe burns with deep ulcerations. Pain and irritation are evident within 3 minutes, but contact with dilute solutions may not cause symptoms for several hours. Contact with the eye may produce pain and irritation, and in severe cases, clouding of the eye and blindness." Solutions as weak as .12% have shown to destruct healthy skin cells within one hour. Other studies acknowledge Sodium Hydroxide as a strong irritant that is corrosive to the skin, eyes, and respiratory tract, but that the severity of the effects are related directly to concentration and pH levels, as well as the length of exposure and skin type.