30 COMPANY PERSPECTIVE
This has been a key strength of Innospec
ever since as the knowledge has been passed down through subsequent employees. It was this skill at combining surfactants that meant that these became practical options for rinse- off cleansing, despite the dominance of SLES. One of the limitations of the SCI technology was the low water solubility. This was not a problem for the cleansing bar
market, which was the main destination for SCI. However, especially in Europe, the demand for bars for body cleansing was reducing and liquid formulations were needed. In 2009, Innospec launched Iselux (Sodium Lauroyl Methyl Isethionate) - then called Pureact SLMI-85. This launch was reported in Personal Care magazine in April 2009 (see Figure 2).
Superior characteristics The launch of Iselux gave formulators the option to create excellent shampoos, cleansers and shower gels that did perform as well as SLES systems. SCI had been on the market previously, and the chemistry is similar to Sodium Lauroyl Methyl Isethionate. Yet the methyl group of sodium lauroyl methyl isethionate has a couple of key benefits that sets Sodium Lauroyl Methyl Isethionate apart from SCI. Any surfactants with ester linkages are
vulnerable to acid hydrolysis. If they are formulated in low pH systems, evidence of hydrolysis may be observed. The fatty acid is released from the surfactant molecule causing cloudiness, an increase in viscosity and formulation instability. For SCI, the pH this starts to be observed
is below approximately pH 6. The addition of the methyl group on Sodium Lauroyl Methyl Isethionate gives stearic hindrance to the ester linkage and therefore protects the ester group from acid hydrolysis. This allows it to be used down to approximately pH 5.5 without these issues.
The methyl group on Sodium Lauroyl Methyl
Isethionate also gives greater water solubility with clear formulations possible at high levels of active, whereas SCI can only be used at 1-2% in a clear system. SCI remains a good choice for solid syndet bars and for paste textures due to its lower water solubility. SCI produces a lower foam volume and a
smaller bubble size compared to the mixture of large and small bubbles that Sodium Lauroyl Methyl Isethionate produces. This makes Sodium Lauroyl Methyl Isethionate ideal for shampoos and SCI better suited for facial cleansers where a creamy lather is preferred. Sodium Lauroyl Methyl Isethionate also
has a faster flash foam. Slow flash foam is a common issue with sulfate-free surfactants and is a large component of this perceived reduced performance compared to SLES.
Product range expansion With the first Sodium Lauroyl Methyl Isethionate product launched in 2009 being the solid flake, there was soon demand for a cold
PERSONAL CARE August 2025
Figure 2: In 2009, Innospec launched Iselux (Sodium Lauroyl Methyl Isethionate) - then called Pureact SLMI-85
process liquid grade and Iselux LQ-CLR was launched in 2010 as a 32% aqueous solution. A similar need for cold processable and
easy to use blends led to the launch of Iselux SFS (Sodium Lauroyl Methyl Isethionate (and) Cocamidopropyl Betaine (and) Sodium Cocoyl Isethionate (and) Sodium Methyl Oleoyl Taurate) in 2011. This is a ‘just add water’ blend to create an easy-to-use sulfate-free cleansing chassis.
Preservative choice changes A notable change in the last 25 years has been the choice of preservative. The industry has moved away from parabens, isothiazolinones and, to some extent now, phenoxyethanol. This has been a true mix of consumer requests and regulatory factors. This shift has been reflected in the Iselux
range with the addition of ‘SB’ grades where sodium benzoate is used to preserve. While developing these products, it was noted that the pH of the solution did not need to be adjusted as low as would be expected to achieve adequate preservation. A study in 2022 showed that actually Sodium
Lauroyl Methyl Isethionate shifts the pKa of sodium benzoate and, therefore, there was more of the active protonated form at a higher pH.4
This can be utilised also in formulation as
challenge testing showed sodium benzoate was still effective at pH 6.5 in an 8% solution of Sodium Lauroyl Methyl Isethionate. The pH of shampoos and cleansing
formulations have got lower, especially in Europe, to accommodate the presumed need of sodium benzoate but, if Sodium Lauroyl Methyl Isethionate is wished to be used, it may be possible to have a higher pH than would be expected, and a pH that means Sodium Lauroyl Methyl Isethionate is also stable.
Blending the rules To support the market, Innospec has launched a number of blends skilfully incorporating Sodium Lauroyl Methyl Isethionate. The first of these was the launch of Iselux Ultra Mild (Sodium Lauroyl Methyl Isethionate (and) Cocamidopropyl Betaine (and) Sodium Methyl Oleoyl Taurate (and) Lauryl Glucoside (and) Coco-Glucoside) in 2013 due to a rise in baby products. This is a cold processable, optimised blend with very high levels of mildness. Furthermore, in 2013, Iselux SLC (Sodium
Lauroyl Methyl Isethionate (and) Sodium Lauroamphoacetate (and) Cocamide MIPA) was launched. This is a cold processable blend that allows for structured liquid systems, white lotion-like formulations with high foam, to be
O O Figure 3: Pureact I series (Sodium Cocoyl Isethionate)
www.personalcaremagazine.com SO3 Na
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