Sodium Hydroxide in Skincare: Why a Strong Alkali Is on Your Acid Toner Label

Sodium hydroxide sounds alarming, but in a finished skincare product it's a pH adjuster used in small amounts, not a skin active. Our take: it's a behind-the-scenes tool that helps acidic formulas land at the right pH, and the label name is scarier than the job. The EU limits it to a pH below 11 when used this way.

What is sodium hydroxide?

Sodium hydroxide (INCI: Sodium Hydroxide) is a white inorganic compound, also called caustic soda or lye. In its neat, concentrated form it is corrosive. That's the version used in drain cleaner and in hair relaxers, and it's the reason the name sounds alarming on an ingredient list.

In a finished skincare product, it plays a very different role. Formulators use it as a pH adjuster.

Many active ingredients, such as acids, need an acidic environment to work as intended, but a formula that is too acidic can be harsh. A small amount of sodium hydroxide is used to nudge the pH up to the target.

That's why a strong alkali can appear on the label of an acidic toner or serum. Its job is to set the final pH of the product.

What does sodium hydroxide do for skin?

Sodium hydroxide is not a skin-active ingredient. It doesn't hydrate, exfoliate or soothe. Its function is on the formulation side: helping a product land at a stable, intended pH.

Why that matters comes down to skin pH. A review in Cosmetics reports that skin surface pH is acidic, with measured values ranging from about 4.1 to 5.8 depending on body site, and that an acidic surface supports barrier function and the skin microbiome. The same review notes broad agreement that topical products should sit in a pH range of 4 to 6. Product pH can be set with several adjusters, and sodium hydroxide is one of the tools used to get there.

pH is one factor among many, and the whole formula determines how a product behaves.

Why we use sodium hydroxide

Sodium hydroxide is in our Glow, Calming Collagen and AHA/BHA products as a pH adjuster. Our formulator uses it to bring each formula to the right pH, so the acid-based products land where they're meant to.

Our view: if a formula needs an acid, it also needs something to set the pH properly, and we'd rather tell you that than hide it.

Who is sodium hydroxide good for?

Because it's used in small amounts as a pH adjuster, most people never notice sodium hydroxide as an ingredient. Skin reactions to leave-on products usually come from the formula as a whole, not from a pH adjuster in isolation.

Take extra care if your skin is reactive, damaged or very sensitive, or if you've had reactions to acid-based products before. Skin barrier state and the other actives in a product matter more than any one pH adjuster.

A patch test is a sensible first step with any new product. Our guide explains how to patch test skincare properly.

Separately, never use neat sodium hydroxide or home-made mixtures of it on skin. That's a different thing entirely and can cause serious burns.

How do you use it?

You don't use sodium hydroxide on its own. It's already part of the formula, and you simply use the finished product as directed on its label. Don't add alkaline ingredients to your products, and don't try to adjust a product's pH yourself.

If a product with a pH adjuster stings, tingles unusually or leaves skin red, stop using it and speak with a doctor or pharmacist if it persists.

What does it pair with?

Sodium hydroxide is chosen alongside the acids and buffers it works with. In acid-based products such as glycolic acid, salicylic acid and citric acid, it's the counterpart used to move the pH toward the intended point. You can read more about how these acids differ in our guide to AHAs, BHAs and PHAs.

As a consumer, there's nothing you need to avoid combining it with, because you're not applying it separately. The practical point is about the whole routine: layering several acid-based products can add up, so introduce them gradually.

What does the research say?

The short version: well reviewed for safety, with the key distinction being concentrated products versus pH adjustment in a finished formula. Hair straighteners and depilatories carry specific limits and instructions, while pH adjustment in a finished formula is regulated in the EU through a pH ceiling.

On skin pH, Lukić, Pantelić and Savić (2021) reviewed how product pH interacts with the skin. They report that alkaline soap raises skin surface pH substantially, with recovery taking hours, and that cleansers above pH 6 have been linked to irritation in some studies.

They also note it's hard to isolate pH from other formula differences, that buffering capacity is rarely reported, and that skin can buffer itself back to baseline. In other words, pH matters, but it's not the whole story.

Safety and regulation

CIR (USA). The CIR Expert Panel assessed sodium hydroxide in its 2021 report, Safety Assessment of Inorganic Hydroxides as Used in Cosmetics, which names Calcium Hydroxide, Magnesium Hydroxide, Potassium Hydroxide and Sodium Hydroxide.

The panel concluded these ingredients are safe in hair straighteners and depilatories under conditions of recommended use, with skin contact minimised, and safe for other present practices of use when formulated to be non-irritating. The report is available via SAGE.

European Union. Sodium hydroxide and potassium hydroxide share an entry (15a) in Annex III of the EU Cosmetics Regulation, which lists substances with restrictions.

As reproduced in Commission Regulation (EU) 2016/622, the limits are: up to 5% in nail cuticle solvents, up to 2% in hair straighteners for general use, up to 4.5% in hair straighteners for professional use, a pH below 12.7 as a pH adjuster in depilatories, and a pH below 11 for other uses as a pH adjuster. The pH adjuster entries set a pH ceiling for the finished product, not a percentage.

Sodium hydroxide in Dope Skin Co products

Sodium hydroxide appears in the full ingredient list of these products:

• Glow Tonic
• Glow Serum
• Calming Collagen Serum
• AHA/BHA Exfoliating Tonic
• AHA/BHA Resurfacing Serum
• Calming Collagen Tonic

Not sure where to start? Try our skincare quiz.

Frequently asked questions

Is sodium hydroxide safe in skincare?
The CIR Expert Panel found sodium hydroxide safe under its conditions of recommended use, and the EU sets a pH ceiling of below 11 when it's used as a pH adjuster. Individual tolerance still varies, so patch test new products.

Why is a strong alkali in an acidic product?
Acidic formulas often need their pH raised to a target level. Sodium hydroxide is one of the ingredients used to do that.

Is it the same as drain cleaner or hair relaxer?
The same chemical, but a very different context. Neat sodium hydroxide is corrosive. In a finished product its role is pH adjustment, and the EU limits the product pH.

Does it make a product pH-balanced?
No. It's one tool for adjusting pH, and the final pH depends on the whole formula. Be wary of broad "balanced" claims.

Can I see how much is in a product?
No. Ingredient lists show the ingredients in order of content, but not exact amounts.

Related ingredients

If you're reading about pH and acids, you may also like citric acid, glycolic acid, sodium PCA and calcium gluconate. Browse the Glow Tonic or AHA/BHA Resurfacing Serum to see full ingredient lists.

Sources

• Burnett CL, et al. (CIR Expert Panel). Safety Assessment of Inorganic Hydroxides as Used in Cosmetics. International Journal of Toxicology 2021;40(2_suppl):16S-35S. SAGE Journals.
• European Commission. Commission Regulation (EU) 2016/622 amending Annex III to Regulation (EC) No 1223/2009 (entry 15a). legislation.gov.uk text of the Regulation.
• Lukić M, Pantelić I, Savić SD. Towards Optimal pH of the Skin and Topical Formulations: From the Current State of the Art to Tailored Products. Cosmetics 2021;8(3):69. MDPI.