Sodium Hydroxide – What Is Lye? How Is Lye Used In Skincare?



What Is Sodium Hydroxide?

Sodium hydroxide is a highly alkaline ingredient that is used in small amounts in cosmetics and skincare products to establish and hold the pH of a product.

Sodium hydroxide, also known as lye or caustic soda, is a white solid compound that is used for its basic or alkaline properties, think opposite of acidic. Sodium hydroxide has a pH value of 13, which means that it is highly basic, or alkaline and is mainly used in the manufacturing of soaps and cleansers.

If you are familiar with lye you may have heard some scary things. As sodium hydroxide is highly basic it is caustic, making it a great product to clean drains and strip away grease and grime. I understand if you are concerned about using such an ingredient in your skincare but sodium hydroxide has a little hidden talent. Sodium hydroxide is used to saponify oils, meaning that it allows oils to lather and foam in soaps and cleansers. During this process, the sodium hydroxide is actually completely used up in the reaction and isn’t present in the final product. 

Sodium Hydroxide

the good: Soaponifies oils so that they can be used in soaps and cleansers.

the not so good: Sodium hydroxide is highly caustic but it is usually fully used up in the process.

Who is it for? All skin types except those that have an identified allergy to it.

Synergetic ingredients: Works well with most ingredients

Keep an eye on: There are many other uses of sodium hydroxide, including dye, drain cleaner, soaps, nail products and makeup. It is good to keep in mind that sodium hydroxide is a versatile ingredient.

What Products Contain Sodium Hydroxide?

Sodium hydroxide was historically used in the formulation of soaps but is also found 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, skincare products.

Why Is Sodium Hydroxide Used?

The main function of sodium hydroxide in cosmetics and personal care products is to establish and hold the pH of a product. In chemistry, pH stands for ‘potential hydrogen’ and it refers to the level of acidity or alkalinity in a given solution. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.

The skin’s normal pH is slightly acidic, typically between 4.5 and 5.75. This acidity of the skin is termed the skin’s ‘acid mantle’ and is maintained by sebaceous glands, sweat glands, and normal skin flora. The acid mantle provides a film of amino/lactic acids and oils that effectively protect skin from environmental factors such as bacteria, allergens, and pollutants that contribute to premature aging and irritation.

The pH of cosmetics and skincare products is important to maintain the skin’s normal pH as closely as possible. On one hand, if a product is too acidic it may irritate the skin or cause a stinging sensation. On the other hand, a product that is too alkaline is detrimental because it depletes your skin of vital, natural fats or lipids. Additionally, a disrupted acid mantle will not allow for products to absorb into the skin as well.

Even though typical formulations only use a small amount of sodium hydroxide in order to adjust the pH, which is usually used up in the chemical reaction, if a product is too alkaline it can damage your skin. This is why knowledgable formulators are so important. In fact, a study on skin products found that using an alkaline cleanser, even once, can do significant damage to the skin as an alkaline cleanser disrupts the skin’s acid mantle. Consequently, this alters the bacterial flora composition on the skin and the activity of the enzymes in the upper layers of skin, as these have an optimal pH level. And the damage is cumulative: the longer you use it, the more damage it does to your skin. Most dermatologists don’t recommend alkaline cleansers despite their growing popularity. 

Is Sodium Hydroxide Safe?

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. 

Sodium hydroxide 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. In most cases, the sodium hydroxide is not present in the final product. In cases where it is, the pH is usually carefully managed so as to not disrupt the skin. 

The United States Food and Drug Administration has approved sodium hydroxide as GRAS (Generally Recognized as Safe) as a direct food additive. However, it is primarily used in the washing and chemical peeling of produce.

Other Uses

In addition to its presence in cosmetics and personal care products, sodium hydroxide is used in many different industries, for instance, 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 tons, while demand was 51 million tons.

Cosmetic Ingredient Review, 2015. ‘Safety Assessment of Inorganic Hydroxides as Used in Cosmetics, Cosmetic Ingredient Review Expert Panel.



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