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Sodium Hydroxide is more commonly known as lye. It has a number of industrial uses and you’ve probably used it before to unblock your drains!

This stuff is pretty harsh.

Understandably there are many people reluctant to use it in their shampoos or personal care products. It’s known to cause contact dermatitis in people So we thought this was worth further study to give you the information you need to make your own informed decision on whether you want to use it.

In this article:

What is sodium hydroxide?
A brief history of sodium hydroxide
Why is sodium hydroxide added to shampoo?
What are the risks?
What are the risks?
The best sodium hydroxide free dandruff shampoos
References.

What is sodium hydroxide?

Sodium hydroxide or ‘lye’ is a strong alkali, used in many different industries to reduce the acidity of chemical reactions. It has many uses, from being used as a drain unblocker ‘dissolving’ grease and proteins, to adjusting the pH of injectable medicines that would otherwise damage blood vessels.

Sodium hydroxide is highly reactive and corrosive, with concentrated solutions causing: skin burns, corneal damage, chemical pneumonitis, and perforation of the gastrointestinal tract [1]. Incidents involving sodium hydroxide are among the most common workplace chemical accidents, but is also an ingredient in every commercial shampoo – why?

A brief history of sodium hydroxide

Sodium hydroxide was formally ‘invented’ in the early 1800s when Sir Humphry Davy isolated ‘sodium hydroxide’ from the crude alkali mixture of ash and rainwater [2]. For centuries before this, sodium hydroxide was used by different populations to make soap.

Soap making is a relatively simple chemical process, in which fatty triglycerides react with sodium hydroxide, to produce fatty acids – crude soap, which forms a lather when mixed with water [3]. Sodium hydroxide is still used in the industrial manufacture of modern detergents, but in more complex reactions, producing purer compounds at higher yields.

[Note: Approximately 350million tones of sodium hydroxide are produced each year, mainly through the electrolysis of sodium chloride, known as the ‘chloralkali process’ [4].]

Why is sodium hydroxide added to shampoo?

It’s difficult to imagine an industrially produced shampoo avoiding sodium hydroxide, whether it appears on the ingredient label or not. Depending on the shampoo, sodium hydroxide has three main roles:

As a precursor to the main ingredients (e.g. sodium lauryl sulfate)
To reduce the acidity, so the shampoo doesn’t damage hair
As a ‘relaxer’, to help straighten hair

For points one and two, there is no FDA requirements for the manufacturer to add sodium hydroxide to the ingredient label, as it would be functionally undetectable, exempt under the ‘incidental ingredient’ exception §701.3(1) [5].

For shampoos labeled as ‘straightening’ or ‘hair relaxing’, sodium hydroxide is added in much higher concentrations. At a concentration of around 5-10%, the sodium hydroxide increases the pH, helping to ‘break’ the bonds that make straightening curly hair so difficult (by cleaving the disulfide bonds between cysteine molecules of keratin) [6].

What are the risks?

Concentrated solutions of sodium hydroxide can be incredibly harmful, and cause a considerable number of chemical burns each year. When used in low concentrations to neutralize acidic shampoos, there are no obvious negatives to the use of sodium hydroxide – it would be more harmful to use an acidic shampoo.

Hair relaxers pose more of a risk, as they use stronger concentrations, and are left in the hair for longer. There is a risk of chemical burns to the scalp and controversial evidence that correlates long-term use in African-American women to uterine fibroids – although the mechanism for this is unclear, and seems unrelated to the sodium hydroxide component [7].

What are the alternatives?

There are many alternative strong alkalis and buffer systems (e.g. lithium hydroxide, potassium hydroxide, calcium hydroxide), but each of these is associated with the same corrosive risks as sodium hydroxide. Different alkalis also affect the characteristics of a shampoo. Soluble calcium detergents, for example, generally form less lather compared to sodium detergents.

There are several ‘no lye’ hair relaxers, which instead of using sodium hydroxide to create a strong alkaline solution, use ammonium thioglycate and a hydrogen peroxide wash to more permanently reduce the disulfide bonds of curly hair [8]. The downsides of this process include:

Normally only professionals carry out the procedure
Hair becomes more brittle
The process depletes natural oils

The best sodium hydroxide free dandruff shampoos on the market today

Sodium hydroxide is a strong alkali, and an essential component of many industrial processes. In shampoos, sodium hydroxide has several purposes, but mainly as a precursor and to alter the acidity. There are very few risks to low concentrations of sodium hydroxide in shampoos, but high concentration hair relaxers are generally considered more dangerous. There are several alternatives, but these can alter the characteristics of a shampoo, and are not an inherently lower risk.

If you want to avoid this ingredient – these are our favorite sodium hydroxide free dandruff shampoos on the market today.

Pharmaceutical Specialities Free & Clear Shampoo

Designed to treat Seborrheic Dermatitis, Dry Scalp and Psoriasis

Pharmaceutical Specialties formed in 1974 to “start a company to make better products than were commercially available for people with sensitive skin”. And boy, have they achieved it with this Free and Clear shampoo.

What is perhaps surprising on a website dedicated to dandruff treatments is that this isn’t a dandruff shampoo at all.

It’s rather a "a non-medicated, mild shampoo for sensitive skin and scalp.”

That said, we can’t use a medicated shampoo all the time, and this is my go to shampoo for those “between” washes.

What is sodium hydroxide?

A brief history of sodium hydroxide

Why is sodium hydroxide added to shampoo?

What are the risks?

What are the alternatives?

The best sodium hydroxide free dandruff shampoos on the market today

References

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