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SLS vs. Soap


SLS or Sodium Laurel Sulfate is an alternative to soap (or detergent), and is found in many, many products that most people use.  It is in Dawn dishwashing soap and most shampoos.  Now, there is some health concern in some quarters.  Let’s explore.

Both SLS and soap have long fatty tails, they only differ as to what sort of (sodium-neutralized) acid end-group they have.  Soap has a carbon-based acid, SLS has a sulfur-based acid.

The biggest physical difference is that the sulfate makes a stronger acid/weaker base, meaning if you go to neutral or acidic pH, SLS keeps on trucking where soap becomes a greasy fatty acid.  This means you can have those mild and gentle skin care products, and MOI Labs can make those wonderful, slightly acidic cleaning products like Mainstream and Rapids, that eat lime scale.

A more subtle difference is that soap is “natural” in the sense that it is indistinguishable from things already in your body, while the sulfur group is a foreign body not found in nature that we are not DNA-programmed to deal with.

This stuff has been tested six ways to Sunday and the scientific community is pretty sure this is not a cancer-causer.  A bunch of bad press went out on the internet, but that proved to be a hoax by one company trying to sell green alternatives.

Where things get dicey is if you get it into an open wound.  There is some evidence out there that it slows healing rates.  This makes sense to me, as it is NOT the same thing as what makes up your cell walls, and perhaps the body doesn’t know how to assimilate it or clear it.  So maybe if you have a scalp condition or a cut, washing with SLS might not be as good a choice.  Washing with something is still good to clear out bacteria, of course.

Now, there is a lot of history of phosphorous-type acids causing allergic sensitivity.  Generally they irritate because they want to suck the water out of your skin when in concentrated form.  This triggers a memory in your immune system, and you are thereafter allergic/sensitized to the compound.

There are now some people claiming to have developed an allergic sensitivity to SLS.  Possible, but this beast is so foreign to most biology, somebody needs to look into whether the immune system can even recognize it once exposed.  The original insult generally only comes when the compound damages you in some way, to get the immune system to react, and the only way this is going to damage you is if the stuff is very concentrated (where it acts more like a detergent).

When might we be exposed to damaging concentrations of SLS?  Never straight out of the bottle, but image the following scenario:  You shampoo with the stuff (nearly unavoidable these days), rinse incompletely leaving a residue of SLS, which is then hit with a hair dryer.  Soap would leave behind a fatty acid residue that would be relatively harmless.  SLS might dry out to something more damaging.  In its raw, concentrated form, it is pretty potent stuff, as bad or worse than any detergent.

If I had to bet, I’d say people developing sensitivity to SLS have been exposed to dried residues of the stuff.  So, maybe if you use SLS soaps or shampoos, the lesson is to rinse very thoroughly, and not over-dry your hair, or you too might develop a sensitivity.

Is SLS inherently bad? Or just a tool like fire, or cars, or knives – all of which can hurt you, but we’d be hard pressed to do without?  I hope this article helps people develop a little more critical thinking around the issue so that we can figure this one out.  For now, the low cost and things it can do are the reason we see so much of it.  The obvious value is, well, obvious.  The hidden dangers, as with anything, we need to explore better.



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