Is Sodium Hydroxide in Cosmetics Safe?
Yes. Sodium hydroxide — the same chemical as lye and caustic soda — is added to creams, serums, cleansers and soaps mainly to adjust pH or to turn oils into soap. It reacts with the acids or fats in the formula as it is added, so a well-made product contains little or no free sodium hydroxide, and its final pH is controlled.
The exceptions are products that are meant to be strongly alkaline — lye hair relaxers, depilatory creams and cuticle removers. They are legal and safe when used as directed, but they can burn skin if left on too long.
“Safe for all other present practices of use and concentration” when “formulated to be nonirritating”, and safe in hair straighteners and depilatories under recommended use, with skin contact minimised.Cosmetic Ingredient Review Expert Panel, Safety Assessment of Inorganic Hydroxides, 2021
Normally no concern
- Moisturisers, serums and toners using it as a pH adjuster
- Gels thickened with carbomer
- Properly made and cured bar soap
Follow the directions closely
- Lye (sodium hydroxide) hair relaxers
- Depilatory creams
- Cuticle removers and softeners
- 5,147reported cosmetic uses (CIR, 2015 data)
- pH 4.5–5.5normal skin surface
- pH < 11EU limit for pH-adjuster use
- 2% / 4.5%EU cap in hair straighteners, consumer / professional
What Is Sodium Hydroxide in Cosmetics?
Sodium hydroxide (NaOH) is a strong alkali, listed on cosmetic labels under its INCI name “Sodium Hydroxide”. It is the same chemical sold industrially as caustic soda and in soap making as lye. In cosmetics it works as a pH adjuster, a neutraliser for acidic thickeners and the alkali that turns oils into soap.
Seeing it on a label does not mean caustic soda is sitting in the jar. Ingredient lists show what went into the product, and sodium hydroxide reacts as soon as it meets the acids or fats in the formula. Some soap labels list the oils and sodium hydroxide that went into the batch; others list the soap salts that came out, such as sodium olivate or sodium cocoate. Both describe the same bar.
| Item | Value |
|---|---|
| INCI name | Sodium Hydroxide |
| Other names | Caustic soda, lye, NaOH (not INCI names) |
| CAS number | 1310-73-2 |
| Cosmetic functions | pH adjuster, saponifying agent in soap, neutraliser for carbomer and acidic actives |
| Not to be confused with | Sodium bicarbonate (baking soda) or sodium carbonate (washing soda) — see caustic soda vs baking soda |
Why pH Matters in Skincare
Skin’s surface is mildly acidic, around pH 4.5–5.5. Many active ingredients — AHAs such as glycolic and lactic acid, vitamin C, and carbomer thickeners — are acidic on their own. A small, measured amount of sodium hydroxide raises the formula to the pH the product needs: comfortable on skin, stable on the shelf and still effective.
- Skin surface4.5–5.5
- EU cap, pH-adjuster use< 11
- EU cap, depilatories< 12.7
- 1% NaOH solution≈ 13.4
6 Uses of Sodium Hydroxide in Beauty and Personal Care
Green chips mark uses where the sodium hydroxide is neutralised in the finished product; red chips mark products that are deliberately alkaline and need careful use.
1. pH adjustment
Small additions bring acidic serums, toners, creams and cleansers to their target pH, so actives work without stinging and the formula stays stable.
2. Gel thickening
Carbomer thickeners stay thin until they are neutralised. Adding sodium hydroxide turns them into the clear gels used in hand gels, serums and hair gels.
3. Soap making
Every true soap is made by reacting oils with lye (saponification). In a correctly made and cured bar, the lye is used up and only soap and glycerin remain. More: caustic soda in soap making.
4. Lye hair relaxers
Sodium hydroxide breaks bonds in the hair to straighten it permanently. EU law caps it at 2% for consumer and 4.5% for professional products.
5. Depilatory creams
Used to raise pH so the hair-removing ingredient works. EU law caps the finished product at pH 12.7.
6. Cuticle removers
Softens and dissolves dead cuticle tissue. EU law caps sodium hydroxide at 5% in nail cuticle solvents.
Sodium Hydroxide in Cosmetics: What the Safety Data Says
The independent Cosmetic Ingredient Review (CIR) panel reviewed sodium hydroxide with the other inorganic hydroxides in 2021. It found the ingredient safe in current uses when products are formulated to be non-irritating, and safe in hair straighteners and depilatories under recommended use. What decides safety is the finished product’s pH and buffering, not the percentage of sodium hydroxide on its own.
How much sodium hydroxide is used in real products
| Product category | Type | Max. reported concentration |
|---|---|---|
| Lipstick | Leave-on | 0.26% |
| Face and neck product | Leave-on | 6.9% |
| Other skin care preparation | Leave-on or rinse-off | 10% |
| Bath soaps and detergents | Rinse-off | 12.9% |
Maximum reported levels from the industry survey reviewed by the CIR panel (2015 data, 5,147 reported uses, about half in leave-on skin care). These are amounts added during manufacture, much of which reacts, not safety limits.
When to take care
With relaxers, depilatories and cuticle removers, follow the timing on the pack, protect the skin as directed and rinse immediately if it burns or stings. If any product gets in the eyes, rinse with plenty of water and seek medical advice. People with very sensitive skin should patch test any new product.
EU and US Rules on Sodium Hydroxide in Cosmetics
In the EU, sodium hydroxide is a restricted ingredient listed in Annex III of Regulation (EC) No 1223/2009. The limits apply to the finished product.
| Use | EU limit | Required label warning |
|---|---|---|
| Nail cuticle solvent | 5% max | Contains alkali. Avoid contact with eyes. |
| Hair straightener, general use | 2% max | Contains alkali. Avoid contact with eyes. Keep out of reach of children. |
| Hair straightener, professional use | 4.5% max | For professional use only. Avoid contact with eyes. |
| pH adjuster, depilatories | pH < 12.7 | Keep out of reach of children. Avoid contact with eyes. |
| pH adjuster, all other uses | pH < 11 | None specified |
Concentrations are expressed as sodium hydroxide by weight. Always check the current consolidated text of Annex III before labelling a product.
United States. Cosmetic ingredients, except colour additives, do not need FDA approval before sale. Since the Modernization of Cosmetics Regulation Act of 2022 (MoCRA), the responsible company must hold evidence that each product is safe. Independent reviews such as the CIR assessment are commonly used as part of that evidence.
4 Myths About Sodium Hydroxide in Cosmetics
“Any product with lye on the label will burn my skin.”
In leave-on products it is used to neutralise acids and is used up in the process. The finished product’s pH, limited to below 11 in the EU for this use, is what touches your skin.
“It’s the same thing as drain cleaner.”
It is the same chemical, but drain cleaners contain it concentrated and unreacted. In a cream it is a small amount that has already reacted with the formula. The dose and the chemical state are completely different.
“Natural soap is made without lye.”
All true soap, including handmade “natural” soap and melt-and-pour soap bases, is made with lye. Properly made soap simply has none left.
“No-lye relaxers are always gentler.”
No-lye relaxers swap sodium hydroxide for other strong alkalis, such as guanidine hydroxide, and also work at a very high pH. Both types can burn if misused.
Buying Cosmetic-Grade Sodium Hydroxide in Bulk
Cosmetic and soap plants need sodium hydroxide that is pure, consistent and documented. SUHA International Trading supplies membrane-grade caustic soda pearls 99% and flakes 98–99%, including food-grade material, with a certificate of analysis for every lot, from Mersin (Türkiye) and Jebel Ali (UAE).
Pearls are the usual choice for formulation: nearly dust-free, free-flowing and easy to weigh and dose. Orders are in full-container quantities, so this suits manufacturers and distributors rather than home soap makers.
- FormsPearls 99% · flakes 98–99%
- Production routeMembrane cell
- GradesIndustrial · food grade
- DocumentsCOA per lot · SDS
- Packing25 kg bags, palletised or in jumbo bags
- Minimum order1 FCL, 20ft or 40ft
- LoadingMersin · Jebel Ali · road from Türkiye
Sodium Hydroxide in Cosmetics: FAQ
Related Guides and Products
References
- Burnett CL, et al. Safety Assessment of Inorganic Hydroxides as Used in Cosmetics. International Journal of Toxicology, 2021
- Regulation (EC) No 1223/2009 on cosmetic products, Annex III
- US FDA — Modernization of Cosmetics Regulation Act of 2022
- PubChem CID 14798 — Sodium hydroxide
Reviewed by the SUHA International Trading technical desk. This page is general information, not medical advice; for a skin reaction, speak to a pharmacist or doctor.