66 FUNCTIONAL INGREDIENTS
recovery) nature allows for suspension without viscosity, resulting in sprayable formulations with a wide, non-drip spray pattern. This unique rheology also provides improved spreadability and pick-up. The 3D entangled network that provides suspension capabilities also offers film formation properties, providing an SPF-boosting effect in sunscreens and styling benefits in haircare. The hydroxyl groups on the cellulose polymer provide a conditioning effect that results in reduces combing force and can aid styling including reduced static and flyaways. Microfibrillated cellulose is insoluble in
water, but is highly hygroscopic, and is supplied as a gel or paste of cellulose microfibrils dispersed in water. The high water retention offers non-drying formulations, but its insoluble nature diffuses light, providing a skin blurring soft focus effect with a matte skin finish and soft skin feel that still feels moisturising on the skin, with proven reduction in transepidermal water loss versus a negative control.
Microfibrillated cellulose in emulsions When used in combination with emulsifiers, microfibrillated cellulose performs a stabilising function especially well due to its high storage modulus and robust 3D network keeping emulsion droplets evenly dispersed and preventing coalescence. However, the resulting network is extremely shear thinning, meaning that any viscosity that is imparted at rest, will not impact ‘pumpability’, ‘sprayability’, or play time due to the rapid thinning as soon as shear is applied.
When benchmarked to alternative stabilisers, such as gums or acrylates, microfibrillated cellulose systems always demonstrated the lowest viscosity, producing incredibly fluid and sprayable emulsions. We have also demonstrated that substituting
a co-emulsifier for microfibrillated cellulose in emulsions can reduce viscosity while even improving stability of the system. In a study combining microfibrillated cellulose (HLB 4) with a traditional emulsifier of HLB 11, compared to a traditional co-emulsifier (HLB 4) / emulsifier (HLB 11) blend, the system containing microfibrillated cellulose offered improved stability despite lower viscosity than the system containing a traditional co-emulsifier. Additionally, microfibrillated cellulose has also been shown to reduce the soaping effect imparted by certain emulsifiers and fatty alcohols when applied to the skin. In many ways, its skin feel and performance with reducing soaping is comparable to dimethicone. This makes microfibrillated cellulose a great
‘cure-all’ to problem solve without impacting viscosity or negatively impacting skin feel.
Emulsifiers and skin barrier integrity It is now commonly known that detergents (cleansing surfactants) can be harsh on the skin and disrupt lipid organisation in the skin, impacting skin barrier integrity. However, emerging research is demonstrating that the surface activity of emulsifiers, depending on chemistry and other factors, also have potential to disrupt the skin barrier.
PERSONAL CARE April 2025
Figure 1: Scanning electron microscopy image of entangled 3D network of microfibrillated cellulose fibres
Contact allergy to cetyl and stearyl
alcohols has been reported for many years, especially in eczema sufferers, possibly due to presence of impurities from processing aids. This also applies to sorbitan esters and other emulsifiers.5,6
panellists had a contact allergy reaction to at least 1 of the 15 emulsifiers tested.7 Emulsifiers primarily interact with the
stratum corneum, which is the skin’s most critical barrier. A paper assessing the impact of O/W emulsions on the skin barrier summarised that, overall, W/O macro emulsions improved the skin barrier, whilst microemulsions tend to compromise it and O/W macro emulsions have potential to compromise the stratum corneum but this is emulsifier-dependent.8 Emulsifier interactions with the stratum
corneum can be by denaturation of the keratin filaments or by alteration to stratum corneum lipids. Studies have shown that non-ionic emulsifiers have lower irritation potential than ionic emulsifiers, with ionic emulsifiers typically binding to and denaturing keratin filaments. Although non-ionic emulsifiers are less
likely to cause keratin denaturation, some non- ionic emulsifiers still interact with intercellular lipids in the skin barrier, with potential to cause irritation or disrupt the skin barrier.9 Trans-epidermal water loss (TEWL) is a
widely used measurement to assess skin barrier function. In a small controlled study utilising simple systems of 5% emulsifier with water and mineral oil only, emulsifiers were shown to induce significant differences in TEWL. Of the nine emulsifiers assessed, five increased TEWL in normal skin, implying a loss of skin barrier function. However, in SLS-damaged skin, three
emulsifiers unexpectedly decreased TEWL. The study discussed the possibility of absorption of the emulsifier into the lipid bilayer leading to increased TEWL in normal skin, but decreased TEWL in impaired skin.10 In another study, based on in vitro Franz
cell TEWL measurements, later backed up with In Vivo data, PEG-20 fatty alcohol ether
emulsifiers (PEG-20 cetyl ether and PEG-20 stearyl ether) were shown to significantly impair skin barrier function. In the same study, sorbitan esters and
In a study of 310 patients, 16% of
PEG40 & PEG100 fatty alcohol ethers were deemed to be skin friendly,11,12
showing that
ethoxylation and/or molecular size impacts the emulsifiers interaction with the skin.8,12 For PEG-ylated emulsifiers, potential for skin barrier disruption is impacted by:8,9,13 ■ Hydrophilic chain length – a larger polar head prevents passing through the skin ■ Hydrophobic chain length – shorter chains are more likely to disturb barrier lipids ■ Degree of saturation (double bonds) of the alkyl chain ■ Ethoxylation – fewer EO groups have higher risk of skin irritation ■ Concentration – above the critical micelle concentration, free monomers are more likely to disrupt the stratum corneum The potential for irritation by emulsifiers
is yet another challenge for formulators to overcome. With the irritation potential being both emulsifier chemistry-dependent, and potentially reliant on existing skin barrier integrity of the consumer, there is no obvious choice for emulsifier selection. In fast-paced product development
environments, rather than decipher the data on irritation as another factor in emulsifier selection, it is predicted that formulators may choose to move away from traditional emulsifiers altogether.
Emerging emulsifier-free trend The global emulsifier-free skin care market size is projected to double over the next 10 years, reaching $3.2bn by 2034. The key drivers are the rising consumer preference for clean beauty and natural ingredients, as well as increased awareness of the risks of sensitisation.14 Emulsions offer delivery of oil-soluble
actives in an aesthetically pleasing, cost- effective format, while providing improve play time on the skin versus aqueous systems. A
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