Monday, 18 July 2011

Sodium Hydroxide: Lye is always lye or is that a lie?

I first posted this in 2009, but I think it is now time for a repost because it was one of the questions that was recently asked. This post explains why sodium hydroxide may not be that alarming in a hair conditioner (if it is not one the top 5 ingredients)
Fellow blogger Mikimu found a neat little article which I'll discuss later after I do some research! She found that one of the listed ingredients listed was sodium hydroxide and asks, 'Isn't sodium hydroxide LYE? The same ingredient in many relaxers? Why would anyone endorse applying this product to one's head? I am stumped. Maybe this chemical used in this way isn't harmful. Either way, I'd like to get your take on this please'
This was interesting for me because it was a good opportunity to do some scientific experiments!!. Yes sodium hydroxide is lye and yes at the right concentration it is the bond breaking stuff we naturals don't like. However in science, sodium hydroxide is powerful stuff and much more than lye. If you add it in small quantities (literally 1 drop), it can drammatically shift the acidity of a product, in other words it corrects the pH of the product.
How does this work? 

(Please don't fall asleep on me) I'm going to have to jog your memory back to chemistry in school and talk about acid base reactions!!! The base (sodium hydroxide) reacts with acid to produce a salt and water.

This action means if you add sufficient sodium hydroxide you can change the pH from highly acidic to low acid or neutral or basic.

NaOH + HCl → NaCl + H2O
Sodium-Na , Hydroxide -OH (So NaOH is sodium hydroxide)
HCl - Hydrochloric acid,
NaCl - Sodium Chloride or common table salt
H2O - Water
To be completely accurate, the principle of buffering used in hair and skin products is only slightly different because the acids are different (usually as not as strong as hydrochloric acid) and the reaction is slightly different but as I don't really want your eyes to glaze over, we'll stop the science stuff here. 

Why cannot you just add sodium chloride or a similar salt? Well NaOH is powerful because of the hydroxide (OH) groups. These OH groups are what drive the reaction shown above. 

Can you use something else other than sodium hydroxide? Yes there are other bases that you can use but why would you? This stuff is so effective in small quantities and the resulting salts are harmless (Analogy, orange juice and lemon juice are both acidic but which one would you drink without sugar??). 

What is the difference between NaOH in relaxer and in hair conditioner? The difference is concentration and therefore pH. Relaxer has sufficient amounts to keep the solution basic, other products such as conditioner will have enough to keep it slightly acidic to neutral (in most cases).


  1. Thank you for the response and the research...both are very much appreciated!!

  2. go head jc!
    at first i worried about sodium hydroxide in products also but then learned about it being used to balance out the ph. thanks for the very thorough explanation. (i'm an egghead so i enjoy this stuff) i like how you described everything. lol @ "eyes to glaze over". i'm excited to learn about other chemicals you've worked with in your lab and how the results vary based on the amount being used.

  3. Thanks J - egghead here too lol

  4. Here's an interesting one, I make handmade soap using Lye (which is chemically transformed and not present once the soap has finished saponifying so don't scream with horror!!!) and I have to wear safety goggles, a mask, sturdy boots and long sleeved protective clothing when working with it! there is a story in the soapmaking world (not sure if its a myth or truth) that a guy accidentally dropped the lye on his foot and it burned right through everything and ate his skin :0( nasty I know, but jus kind of puts the lye relaxer into a new perspective for me

  5. Thanks for this Jc, i started avoiding conditioners with NaOH in them after i thought about the "lye" situation, then remembered that the concentration actually matters (as with a lot of things). I was also one of the people who asked you for your opinion on this, so i am thankful for the answer! :)

  6. Thanks for the clarity in this article. I see a lot of people ditching conditioners with sodium hydroxide in them.

  7. what's shocking me is the fact that people is much horrified by sodium hydroxide at the end of an ingredient list, much more than paraben which is more bad on health. For example, in mimuku article, nothing about the preservative which is totally more alarming then sodium hydroxide..

  8. Revive - it is all about concentration. In soap making the lye is highly concentrated at the start but not at the end.

    Chrys actually parabens are not that much of a worry to me. Taking the contraceptive pill is much more risky than parabens.

  9. Nice read. Chrys, just wanted to let you know that the FDA rules that any ingredient added at less then 1% can be added ANY WHERE on an ingredient label. So many companies choose to list the 1% or less healthy ingredients at the top. Pretty deceiving, I know. But remember that labeling laws are different in foods than in cosmetics.


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