Sodium hydroxide, known as lye or caustic soda, is a versatile ingredient in the hair care industry, especially for curly hair. It not only acts as a chemical relaxer to straighten curls but also helps maintain the pH balance of hair products, preserving hair health and preventing damage. Despite its benefits, the potent nature of sodium hydroxide calls for careful use, particularly in its role as a hair relaxer.
To ensure the accuracy and depth of our exploration into sodium hydroxide in hair care products, I’ve enlisted the expertise of a friend who is not only a seasoned cosmetic formulator but also holds a PhD in Chemistry. With his extensive knowledge in the science of hair care formulations and a keen understanding of chemical interactions, he provides a balanced overview of sodium hydroxide’s chemical properties, its applications in hair care, and the precautions to consider, helping us make informed decisions about the products we use on our hair.
What is Sodium Hydroxide?
Sodium hydroxide, commonly known as “Lye” or “Caustic Soda,” is an essential inorganic chemical compound with widespread applications in various industries, including cosmetics and personal care products. As an alkali or base, it readily dissolves in water, creating a high pH solution. This characteristic makes it valuable for adjusting the pH of formulations in cosmetic products.
In soap making (including shampoo bars), sodium hydroxide is a key ingredient, combined with vegetable oils to initiate the saponification process, creating soap. Additionally, its cleansing and solubilizing properties make it an integral component in both household and industrial detergents.
Overall, sodium hydroxide’s versatility and significance make it a crucial ingredient with diverse uses in numerous applications.1
Physical and Chemical Properties
| Chemical Name: | Sodium Hydroxide |
| Common Name: | Caustic Soda |
| Chemical Formula: | NaOH |
| Molecular Weight: | 40.0 g/Mol |
| Physical Appearance: | Crystalline Solid |
| Nature: | Alkaline, Basic |
| Solubility in Water: | Highly Soluble at Room Temperature |
| pKa (Acidity): | 15.7 (Strongly Basic) |
| pH of 1.0% Solution | 13.0 |
Role of Sodium Hydroxide in Hair Products
The role of sodium hydroxide in hair care products can be classified into two main applications. Firstly, it serves as a buffering agent, responsible for adjusting and maintaining the desired pH level of the finished product. Secondly, sodium hydroxide acts as an active ingredient in hair straightening products.
pH Adjustment
Hair care products have diverse pH requirements depending on their main function. For instance, the pH levels of a shampoo and rinse-off conditioner typically falls within the range of 4.00 – 5.00, achieved by adding either an acid or a base.
In this case, sodium hydroxide is employed as a strong base to raise the pH level to the desired range on the pH scale. Due to its high pKa value, only a small amount of sodium hydroxide is needed for effective pH adjustment.2,3,4
On the other hand, hair styling gels necessitate a neutral pH level of 6.50 – 7.50. These gels often contain carbomer, a strongly acidic thickening and styling polymer. To neutralize the carbomer and achieve the desired pH, sodium hydroxide is a preferred choice due to its cost-effectiveness.
When examining the ingredient lists of these formulations, sodium hydroxide is typically found listed towards the end, indicating that only a small quantity is required for pH adjustment. This highlights the precise and economical usage of sodium hydroxide in hair care product formulation.
Active Hair Straightening Ingredient
Hair straightening products, commonly known as hair relaxers, are powerful alkaline creams that incorporate inorganic alkalis such as sodium hydroxide, lithium hydroxide, or guanidine hydroxide. These relaxers have gained immense popularity among individuals with Afro-American hair, as they provide a means to straighten excessively curly or coily hair.
Specifically, hair relaxers containing sodium hydroxide are referred to as “Lye Relaxers,” while those containing other hydroxides are known as “No-Lye Relaxers.” These products originated in the early 1940s and have since undergone significant research and development efforts to enhance their efficacy and safety, resulting in a continuous growth in demand and popularity.5
Chemistry of Hair Straightening
Chemically straightening curly hair fibers involves breaking the existing disulfide chemical bonds within the hair protein structure. Sodium hydroxide plays a crucial role in this process by providing hydroxide ions that target the disulfide bonds.
Subsequently, under alkaline conditions, a chemical rearrangement occurs, leading to the formation of new lanthionine bonds. This transformation of the keratin protein’s chemical structure results in the straightening of coily, curly hair.
The level of straightening achieved depends on the amount of sodium hydroxide present in the relaxer cream formula. In essence, the more sodium hydroxide, the greater the extent of straightening.5
Impact of Using Sodium Hydroxide Relaxer
Sodium hydroxide is a potent and corrosive chemical compound, making it a risky choice for chemical hair straightening. The process can lead to considerable damage to the hair fibers, causing them to become weak, brittle, and highly porous.
A typical sodium hydroxide cream relaxer boasts a pH of 13.0 and contains approximately 2.00 – 3.00% active sodium hydroxide. Consequently, the hair fibers may undergo significant swelling, physical rupture along the hair shaft, and removal of cuticles from the outer layer. As a result, the hair becomes dry, rough, and frizzy.
Maintaining healthy hair after chemical straightening requires a tailored care routine to revive its natural appearance, texture, and luster.
Hydration, emollience, and fiber softening become crucial aspects addressed by hair care products designed for chemically treated hair. It is essential to exercise caution and provide appropriate aftercare to maintain the health and appearance of chemically straightened hair.6,7,8
Is Sodium Hydroxide in Hair Products Safe or Harmful?
Sodium hydroxide, being a potent base, can cause severe irritation and skin burns upon direct contact with the skin. However, in hair care formulations, its safety depends on the intended use and adherence to regulations. When used within the permissible concentration range as set by regulations, it becomes safe and does not harm the skin or hair fibers.
Hair straightening products may contain higher concentrations of sodium hydroxide (ranging from 2.00% to 3.00%). As a result, careful handling and safety measures are necessary during their application.
Direct contact with the scalp should be avoided, as this sensitive area may react quickly to topically applied sodium hydroxide. Nevertheless, when used according to instructions and in appropriate concentrations, sodium hydroxide is considered safe and can be used effectively in hair straightening products.
What Should You Do If a Hair Product Contains Sodium Hydroxide?
No need to worry. To determine the safety of a product containing sodium hydroxide, examine the ingredient listing on the back of the product label.
For shampoos, conditioners, or hair styling gels, the amount of sodium hydroxide used is typically small and does not pose any threat to the scalp or hair fibers. In such cases, sodium hydroxide will be listed toward the end of the ingredients list.
For hair straightening products, manufacturers usually mention the name of the active ingredient and the concentration level used. Regardless of the product, there is no need to fret about sodium hydroxide in your hair care product. Just make sure to read and follow the instructions provided.
However, if you experience any discomfort or irritation, discontinue use of the product and consider reaching out to the manufacturer or a dermatologist for further guidance. Your safety and satisfaction are of utmost importance.
Summary
Sodium hydroxide is a common ingredient in hair care products, serving either as a pH adjuster or an active component in hair straightening products.
Rest assured, it is always used within regulatory limits and does not pose any threat when used as intended. In shampoos, conditioners, or hair styling gels, sodium hydroxide is utilized in small, safe amounts that do not harm the scalp or hair.
However, for hair straightening products, it is advisable for consumers to conduct a patch test before applying the relaxer cream to ensure individual tolerance and safety.
References
- Schumann, K.; Siekmann, K., Soaps. In Ullmann’s Encyclopedia of Industrial Chemistry, Ullmann, F.; Bohnet, M., Eds. Wiley-VCH: 2003. ↩︎
- Corbett, J. F., The Chemistry of Hair-care Products. Journal of the Society of Dyers and Colourists 1976, 92 (8), 285-303. ↩︎
- Zviak, C., The Science of Hair Care. Taylor & Francis: 1986. ↩︎
- Corporation, A. P., Hair Care: From Physiology to Formulation. Allured Publishing Corporation: 2008. ↩︎
- Johnson, D. H., Hair and Hair Care. Taylor & Francis: 1997. ↩︎
- Ruetsch, S. B.; Yang, B.; Kamath, Y. K., Cuticular damage to African;American hair during relaxer treatments; A microfluorometric and SEM Study. Inter. J. of Cosmet. Sci 2009, 31 (3), 244-245. ↩︎
- Khumalo, N. P.; Stone, J.; Gumedze, F.; McGrath, E.; Ngwanya, M. R.; de Berker, D., Relaxers’ damage hair: Evidence from amino acid analysis. J. Am. Acad. Dermatol. 2010, 62 (3), 402-408. ↩︎
- Syed, A. N.; Habib, W. W.; Kuhajda, A. M., Water-soluble polymers in hair care – Prevention and repair of damage during hair relaxing. In Water Soluble Polymers: Solution Properties and Applications, Amjad, Z., Ed. Plenum Press Div Plenum Publishing Corp: New York, 1998; pp 231-244. ↩︎
