What's in your Shampoo? Part 3 - SLS

Dear readers,

Let's resume our journey through our new mini-Series "What's in your Shampoo" with this 3rd instalment focusing on Sodium Lauryl Sulfate (SLS) and Sodium Laureth Sulfate (SLES) and a note on Ammonium Lauryl Sulfate (ALS).

You can catch up on the first two parts:

Part 1 - Shampoo Recipe Making

Part 2 - Parabens

Throughout my research, I have found countless "serious" websites that tell a very convincing story but most are completely confused between SLS and SLES! Sometimes coming from "sciency" websites, it is absolutely shocking, no wonder non scientists can't make head from tail of SLS business!!! I hope this article will clear any confusion. Personnally, I don't suffer from dermatitis or allergies, so my skin agrees with detergents very well, I don't worry about them anymore!

SLS, SLES, ALS

Structures

* Sodium Lauryl Sulfate, SLS, is an organic compound with the formula CH3(CH2)11OSO3Na, it is a.k.a. Stepanol wac, Stepanol waq, Natriumlaurylsulfat,Richonol af, Duponol qx, Perlandrol L, Perlankrol L.

* Sodium Laureth Sulfate, a.k.a. SLES, Sodium LaurylEther, Tergentol, Sodiumlaurylglycolether sulfate, HSDB 6143,Sodium lauryloxyethoxyethyl sulfate, Sodium lauryl di(oxyethyl) sulfate, EINECS221-416-0, Sodium polyoxyethylene lauryl sulfate, Sodium dioxyethylenedodecylether sulfate, 2-(2-Dodecyloxyethoxy)ethyl sodium sulfate, Lauristyl diglycolether sulfate sodium salt, Sodium 2-(2-dodecyloxyethoxy)ethyl sulphate, Sodiumlauryl alcohol diglycol ether sulfate, Sodium diethylene glycol dodecyl ethersulfate, Lauryl diethylene glycol ether sulfonate sodium, PEG-(1-4) Laurylether sulfate, sodium salt, LS-195344, Diethylene glycol monododecyl ethersodium sulfate, sodium 2-[2-(dodecyloxy)ethoxy]ethyl sulphate

* Ammonium Lauryl Sulfate, a.k.a. ALS, sinopon, presulin, neoponlam, siponla30, siprol422, siproll22, Texapon A, maprofixnh, richonolam, sterlingam

Synthesis

They are naturally derived from fatty oils which are occurring in various plant - and animal sources - such as Coconut oil, Palm kernel oil, Soy beanoil. As such, they are readily biodegradable.

For SLS and ALS, they are synthesized from lauryl (a.k.a. dodecyl) alcohol which derives from the oil by hydrolysis followed by hydrogenation. The alcohol is then processed by sulfation, the product is then neutralised by Sodium Hydroxyde (to give SLS) or Ammonium Hydroxide (to give ALS).

Synthesis of SLS - From HERE

For SLES, lauryl alcohol is transformed by ethoxylation. It is this process that produces potentially toxic by-products such as 1,4-dioxane (see Cause for Concern):

1,4-dioxane structure

Uses

* They are anionic surfactants used for their detergent capacity.

Figure 1. Oily material is represented
by the beige sphere in the middle and the
detergent by purple spheres linked to blue tails

Detergents have the ability to surround oily materials and allow them to be rinsed away by water (fig.1). These surfactants (another name for detergents) can be anionic (negatively charged), cationic (positively charged), zwitterionic (both charges) or non ionic depending on the charge of their hydrophilic polar group (purple spheres):

SLS, SLES, ALS are used in cleaning products for their cleansing properties and bubbling effect. It is found in higher concentrations with industrial products and in lower quantities in toothpaste, shampoos, shaving foams and bath creams. But they are also used in moisturisers and other– what is called – leave-on products (see What happens on our skin).

Note: SLS is responsible for your altered perception of taste after brushing your teeth.

* It is also used in laboratory to aid in breaking down cells to release their DNA and study their proteins. Scientists more commonly know SLS by the name SDS.

* In medicine, SLS is also used as a laxative, and as a component of dissolvable aspirins or other caplets.

Cause for concern? * Irritation - The degree of irritation is assessed by measuring the skin hydration, blood flow and thickness. SLS and SLES have both been shown to be skin (and eye) irritants, at concentrations of 10%. The toxicity is acute and local. It has to be noted that all studies are done on animals -not humans- and at very high dosages. So in any scientific article, it would always be concluded that our consumer habits only bring us low health hazards. As a rule, a concentration of maximum 2% is recommended in cosmetics and 1% in leave-on products (wherease studies showing any signs of irritation typically use 10%).
Note on eye irritant potential: so is lemon juice and cola... So when you read info, all is relative and needs to be put back into perspective.

* Skin sensitiser - As it has been shown to require an initial application of 10% SLS, it has been decided that it was unlikely that SLS has skin sensitisation potential. However, for people who suffer from skin problems, SLS can affect them with chronic skin hypersensitivity.

* Aphteous ulcers (Canker sores) - SLS in toothpaste, however in small concentrations, can cause the recurrence of these, and many studies have shown that using a SLS-free toothpaste decreased the occurence or length of symptoms.

* Genotoxicity - SLS does not interact with DNA and doesn't induce gene mutations.

* Cancer - SLS is NOT carcinogenic, nor SLES,  when either applied directly to skin or swallowed. A few years back, some contamination with 1,4-dioxane was detected in SLES, and although no conclusive data shows that it causes cancer at high doses (much much higher than those found in cosmetics), FDA has asked manufacturers to purify their SLES free of 1,4-dioxane (and they did), even though the negligible amount found is not harmful.  The big scare from SLS being cancerous arose when nitrosamines were discovered in shampoos in the 70's!!! Of course, these have been completely removed and checks are in place but unfortunately nowadays with internet, it is very easy to spread an old rumour... So I repeat, SLS/SLES/ALS do not cause cancer!

* Reproductive toxicity - no effect on fertility was seen in a study where male mice were administered high doses of SLS.

* Hair loss - According to the National Toxic Encephalopathy Foundation, this is most likely to be the result of poor rinsing that leaves SLS deposits in your hair follicles. Those deposits penetrate your scalp and could corrode the hair follicle causing hair loss.

Science bit: what happens on our skin?
* Surfactants, like SLS, at high concentrations (typically tested at 10% - cosmetics contain a MAXIMUM of 2%) may damage the skin barrier by several mechanisms: disruption of a skin protein called keratin, changes in lipid structure, inflammatory processes with keratinocyte-derived cytokine release. 
BUT SLS effect depends on how long it is left on the skin and in which dose. Hand washing, for example, leads to a gradual decrease of skin hydration for a short time before it is able to reverse the loss.
* Because of the possible effect of SLS on the organisation of the lipid bilayers, it has been shown that continuous exposure of more than 1h with 10% SLS, it is able to penetrate directly into the skin up to a depth of 5-6mm. Following these studies, it has been advised not to use leave-on products containing SLS such as face masks, moisturisers, and all products that you don't rinse off straight away or check that concentration of SLS doesn't exceed 1%.
* For those of you who have allergy-prone skin, significantly stronger reaction to SLS were found during the winter than the summer vs other detergents. A decreased hydration state of the epidermis of unexposed skin was found during the winter and the scientists say in their article that they believe this to be responsible for the increased susceptibility to SLS during this season.
* For the scientists out there: A few studies also show how our skin is more permeable to other components such as water, nickel, acetic acid and acid ascorbic (vitamin C) but not hydrocortisone (for example), after a continuous exposure to SLS (48h for the study on water, nickel and hydrocortisone; 30min/day for acetic acid and acid ascorbic over 4 days).

Alternatives to SLS

There are no alternatives to SLS that have the same efficient properties! 

SLS is still, for people with no skin sensitivities, perfectly safe (in wash-off products) and effective, and totally natural and green!!!
Less harsh detergents than SLS are SLES (Sodium laurETH sulfate) or ALS but always check the concentration if possible.

However, most people want sulfate-free products and these are available! BUT, and this will be interesting for people with sensitivities, a study in 1999 characterising skin damage and recovery after exposure to different detergents concluded that, should any irritation occur at 2% SLS, the same effects were observed when testing:
5% sodium C12-15 pareth sulfate
5% Sodium Cocoyl isethionate
10% disodium laureth sulfosuccinate
10% cocamide DEA
10% cocamidopropyl betaine (easy blog article to read)
10% lauryl glucoside

So this kind of gives you a nice list to look out for when choosing your products. Don't forget the amount used is also important so don't jump to conclusion too soon.
The sciency bit is:
As a "rule", it has been shown that if the detergent has 12 zig-zags in the blue tail (see fig.1 and SLS structure), it is more likely to have irritation potential. Irritation potential decreases if you increase the size of the purple sphere or the lenght of the blue tail (see fig.1).

I did find an article saying that many products contain Sodium Cocosulfate as a safe alternative to SLS. Because it sounds like a natural compound, people don't doubt the rest of the article saying that it's better than SLS. But a quick google search showed that sodium cocosulfate is SLS but in a less purified form!! So if you have to look for products that need to be milder on your skin for medical reasons, then avoid this one too because it's just another name for SLS!!

Here is a website where they list surfactants you could use to replace SLS, but as for anything DOSES are the key. And don't forget it's not because it says natural or organic that it means that it's safer as they might contain impurities affecting your skin. Also as we are living in new consumer-led era, those products haven't been checked out by scientists as much as SLS has, so they actually might be worse!

All skins are different and, as for everything, you do what you think is best for you... Nobody else will :)
I will finish this post with this self-explanatory pix:

References
Agner and Serup, 1989
Lévêque et al., 1993
Patil et al., 1995
Frankild et al., 1995
Barany et al., 1999
Schwanitz and Uter, 2000

Bellare et al., 2001  

Fluhr et al., 2004
NICNACS Existing Chemicals information Sheet
www.Wikipedia.com
www.Futurederm.com
www.Livestrong.com  

Personal care Truth website

Household and personal products Industry