Sodium lauroyl methyl isethionate

Jul 25, 2022 | Ingredients

Sodium lauroyl methyl isethionate (SLMI) is an alternative to widely known surfactant sodium cocoyl isethionate (SCI). SLMI is a very mild anionic surfactant and can be used as a primary surfactant or as a co-surfactant (secondary surfactant).


1. SLMI basic properties

As sodium lauroyl methyl isethionate is very mild surfactant it can be used even for sensitive skin. It is made from coconut based lauric acid which makes it a natural derived ingredient without using palm oil. It is also biodegradable and sulfate-free.

SLMI basic properties

INCI Sodium lauroyl methyl isethionate (SLMI)
Function Surfactant
Type Mild anionic surfactant, sulfate-free, ethoxylated
Origin It is produced from 100% coconut-based lauric acid
Appearance Hard pale, off white chunks
Scent Has a noticeable characteristic scent
Active matter 80-85%
pH 5.5-7 (10% solution), works in pH of 4.5-8.5
Usage rate For liquid formulations up to 20%, for solid formulation up to 40%
Solubility Water
Other Criteria Vegan
Heating temperature 50-60°C (122-140°F)
Thickening With amphoteric surfactants, gums, salt


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2. How to formulate with sodium lauroyl methyl isethionate?

SLMI has a very good solubility in water compared to SCI. This is why SLMI can be used in a variety of liquid formulations. It can be used in solid formulations as well, though solid bars need more time to harden and they are a bit softer than those with SCI surfactant.

As SLMI dissolves in water well, clear formulations can also be achieved. However, adding a chelator (binds calcium and magnesium ions) may cloud your formulation (it really depends on the used chelator). I have tried to add sodium phytate and the shampoo was cloudy. But this does not bother me.

In some cases you can formulate glossy, shiny formulations as well which I think is very cool. It looks very nice and you don‘t need additional ingredients to have this effect which is neat.

SLMI comes in big chunks and to speed the solubility process those chunks can be grinded into powder. Just remember to use a proper mask as the grinded powder irritates nose and lungs. Also, we want to stay safe when formulating skincare or haircare products.


3. ph of sodium lauroyl methyl isethionate

This surfactant produces dense and creamy foam, has good rinsability and leaves the skin soft and slightly conditioned. It can be used in pH 4.5 – 8.5. However, I would say that the pH is very easily changed in small amounts of lactic acid (80%).

I had a 50 g batch of test shampoo with a pH of 8.3 and added 0.12 g of lactic acid. After mixing it in I have checked the pH again and it was 4.8! I know it that the pH depends on the ingredients used, but this was really unexpected as I have used the same ingredients as before, just added SLMI instead of SCI.


4. Thickening

As with most surfactants, SLMI can be thickened with amphoteric surfactants such as cocamidopropyl betaine.

I have noticed that using SLMI with a bit of SLSa (sodium lauryl sulfoacetate and this is not the same as SLS or SLES) the viscosity increased but not enough for a shampoo. For further thickening I have tried iota karagenaan which worked very well. I think Xanthan gum should also work.

5. What can you make with sodium lauroyl methyl isethionate?

  • shower gels
  • facial cleansing gels
  • hand wash
  • liquid shampoos
  • foaming scrub
  • solid shampoos

6. Where to buy SLMI?

This surfactant is quite new and is a bit harder to find. I got this surfactant from alexmo-cosmetics (Germany). Sodium lauroyl methyl isethionate has a trade name of Iselux, but some suppliers have named it differently (SurfaLux).

You can also get it from:

Sodium lauroyl methyl isethionate can be found in blends of surfactants, for example windypoint.

7. Chemical structure of SLMI

This section is a bonus for those who like to see how the molecules look like. I know that chemistry can be intimidating, but I am a fan of it and lots of things can be explained just by looking at the formula of an ingredient.

We can start to look at the structure with the name of the ingredient.

  • Sodium here is an ion and is written as ‘Na’ with a plus sign.
  • Lauroyl comes from a fatty acid that SLMI is made of . Here we can see its residue and it looks like a long tail.

  • For those who are wondering what is a ‘methyl’ – it is a group -CH3 that is circled in the formula below.
  • And isethio- is the the backbone of isethionic acid.
  • The ending -nate shows that it is a salt.

Chemical structure of sodium lauroyl methyl isethionate


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