HYGIENE 17


1000


100


10


1 without surfactant AKYPO® LF 4


AKYPO® RLM 25


AKYPO® RLM 45 CA Soap SLS SLES


Figure 3: The MIC synergy between Benzalkonium Chloride and Akypo LF 4 in preventing growth of Staphylococcus Aureus.23


hand sanitisers in the US. However, such thickened organic formulations may well gain approval in other countries. At the Prospector database,17


Dr Belinda Carli


demonstrates in a video that illustrates preparation of the hand sanitising gel containing 60% organic ethanol and Keltrol CG-SFT Xanthan Gum of CP Kelco as a structuring agent. The minimal effective concentration of ethanol is compensated here by small additive of the tea tree oil, a well-recognised natural virucide and antibacterial agent.18


This organic sanitiser


prevents skin drying, especially when used several times a day. It is worth mentioning that all essential oils and extracts, like aloe vera, are not compatible with recommended hydrogen peroxide. Some plant and algal derived additives caring against skin dryness, offering soothing and emolliency can be found in the formulation guidelines compiled in Personal Care Magazine. Hand antiseptics, both of hospital-grade


and domestic use, with cationic surfactants have been on the market for a long time (see, e.g. Ref 19). Some salts of quaternary ammonium compounds (QACs) and their synergistic compositions serve a proper biocidal/virucidal effect. Benzalkonium chloride, didecyldimonium chloride, and benzethonium chloride are among the most effective biocidal agents commonly used in the alcohol-free sanitisers. Benzethonium chloride is less common because FDA did not classify this surfactant as GRAS. Cationic surfactants, used due to their biocidal, conditioning and antistatic properties, are often defined in the literature as rather irritating compounds. But occurring skin reactions towards QAC-based hand sanitisers are the result for the most part of the too primitive formulation and the incorrect choice of ingredients. Now, it is


November 2020


possible also to choose rather mild and green cationic biocides, e.g. undecylenamidopropyltrimonium methosulfate and quaternary functionalised alkyl polyglucosides known as SugaQuats.20 Of course, the virucidal and antimicrobial activity of a sanitiser containing such a surfactant could not be speculative. QACs act as polypeptide denaturants


and membrane-active agents, which disorganise the viral envelope, damage the membrane, RNA, and other targets inside. Recent studies of some medical centres have shown that QAC-based hand sanitisers destroy lipophilic viruses, like SARS COV-2, and they are more active against Gram-positive bacteria than against Gram-negative bacilli.8, 19


Cationic-based


formulations are effective against not all types of germs and bacteria and therefore need adequate preservation. In particular, benzalkonium chloride (sold as Acticide BAC 50, Alkaquat DMB-451, Arquad B 50, Barquat MB-50, Empigen BKC 50, Hyamine 3500, Stepanquat 65 NF, Tetranyl BC-80, etc.) was found to inactivate various types of viruses at low concentrations but not as equal and fast as 70% ethanol. Certified virucide blends, such as Bardac 205M/208M, twin C8-C10 chain quaternary ammonium compounds and alkyl dimethyl benzyl ammonium chloride, are proposed by Lonza for sanitiser producers. In general, QACs in 0.1%-0.2% concentration are rather well tolerated and have low allergenic potential. In higher concentrations, though, they can cause irritation to skin and mucous membranes. Chlorhexidine digluconate, broad-


spectrum biguanide-type biocide, has good skin tolerance and becomes popular essentially as the secondary ingredient combined with benzalkonium chloride and other QACs.21


Compared to antibacterial


efficacy, the virucidal activity of chlorhexidine is quite variable and significantly less effective and slower-acting than povidone-iodine.22


Formerly used anti-


microbial triclosan has been in the focus of media attacks at the beginning of this century, which are probably not groundless, regarding its suspected endocrine disruptive effects. Croda supplies Arlasilk PTM (INCI:


Myristamidopropyl PG-Dimonium Chloride Phosphate) for use in personal care products. This coconut-derived multifunctional phospholipid-like amphiphile is composed predominantly of the diester (Fig 4). Arlasilk PTM combines gentle cleansing, conditioning and distinct sensory benefits. Another notable property of this amphiphile consists of the broad- spectrum antimicrobial enhancement, which allows to use it in alcohol-free sanitisers as exemplified by the Formula shown in Table 4. Using Arlasilk PTM allows minimising preservative addition and to create self-preserved compositions.20 It is well known that most anionic


surfactants form an insoluble complex with cationic biocides, namely with quaternary ammonium compounds and chlorhexidine, inhibiting their disinfecting properties. The diagram in Figure 3 shows the minimum inhibitory concentration (MIC) of benzalkonium chloride required to prevent the growth of Staphylococcus aureus in the presence of a fixed quantity (500 ppm) of different added surfactants. Typical anionic surfactants, such as soap, SLS and SLES, inhibit visibly the disinfecting effect of benzalkonium chloride, that makes necessary to increase the concentration of biocide to over 100 ppm. Akypo RLM, the mild “cryptoanionic” ether carboxylate of Kao, exhibits the minor inhibition. In the case of Akypo LF 4 (INCI: Capryleth-9


PERSONAL CARE EUROPE


MIC (ppm)


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