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Sodium hydroxide as a skin irritant
Hello, I’m not a cosmetic chemist but I have a burning desire to know a bit more about sodium hydroxide if anyone has any information to share. For context, I have very dry, rosacea-prone skin, and over the past 5 years or so, I’ve noticed that my skin reacts badly (redness, breakouts) to many products that get longterm rave reviews, even products specifically formulated for sensitive skin. Of course everyone’s experience will vary, but I recently I made a spreadsheet to compare ingredients in those products and the ONE common denominator is sodium hydroxide. I even did a test with a new foundation containing NaOH just to confirm, and sure enough, I started breaking out on day 2. (So sad, it was a sample of the Lisa Eldridge Skin Tint, which is otherwise incredible.)
I was so happy to finally be able to pinpoint my problem ingredient so I can avoid it in the future; BUT in reading further, it seems that IF sodium hydroxide works as it should to regulate acidity, then I’m not actually coming into contact with the sodium hydroxide itself, but rather… salt water? Is it possible that the formulations are imprecise, or vary in manufacturing, so that there’s a bit of undissolved sodium hydroxide left in the formula, and that’s why I’m reacting? Maybe I’m just very sensitive to salt content? I’m confused ha. Would love to figure this out!
Thank you!
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12 Replies
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Very doubtful you’re not encountering NaOH per se.
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Yes that’s what I was wondering… thank you!
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Sorry - very doubtful that you ARE encountering….
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In manufacturing, a batch needs to have its pH raised or lowered to meet specifications. Usually, the pH adjuster is included in the formula and we simply have to add a bit more at the end. However, it does happen that a formula doesn’t have one or it contains an acid but when we measure pH it comes out too low and we need to add an alkaline pH adjuster. We often use sodium hydroxide for this as it’s cheap and we have a lot of it on hand. This would be classified as an incidental ingredient and does not need to be disclosed on the label. So there is a good chance that other products you use also contain sodium hydroxide but don’t include it on the label.
When you say salt water do you mean specifically sodium chloride? That may happen if there are other ionic ingredients in the formula that release a chloride ion when dissociating. Depending on the formula, there could many different sodium salts “formed” but the concentration would be incredibly low. I put that in parentheses because most sodium salts are soluble in water so the sodium would remain as a free floating ion unless all the water is removed.
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To answer your question, I find it highly doubtful that there could be undissolved sodium hydroxide remaining in a product. Sodium hydroxide is not added as a solid. Generally, it is dissolved in water before being added to the product to ensure it disperses quickly and allow the compounders greater precision when weighing it.
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Thanks for your response, that’s so interesting about incidental ingredients!
So there’s not one consistent byproduct as a result of sodium hydroxide being added to a formula? Do you think it would it be possible for skin to react to even a low amount of whatever byproduct of sodium hydroxide remains in the formula?
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No. You should see it far down on the ingredient label and a little sodium will not be an issue.
Maybe the pH of the products bothers you. Look for that on SDS documents.
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Thanks Phil, good idea to check the ph…
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What I’m saying is there are no byproducts unless all the water is removed or there is a molecule that makes an insoluble salt with sodium. The latter is very unlikely because sodium salts are soluble in water with exceptions that wouldn’t generally be seen in cosmetics such as sodium bismuthate. All that will happen is the sodium will hover near cationic molecules or water. If the water is removed, the sodium will then form salts with the cationic molecules it is most attracted to.
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Replace all instances of cationic here with anionic. I replied a bit too early for my brain to be working properly.
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Is there a safe alternative to sodium hydrochloric acid, to raise the pH level, when the compound contains glycosylic acid?
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There is no “sodium hydrochloric acid” and hydrochloric acid like NaOH is ionic so not the parent compound in water but the ions H and Cl. Not much use in cosmetics but perhaps to adjust pH and that at low levels.
Glycolic acid? This is not relevant to either of the above.
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