Focus Preservatives: Chlorhexidine
The difficult period we are all experiencing has led to an exponential increase in the use of sanitising, disinfecting and biocidal products. After ethyl alcohol and sodium hypochlorite, Chlorhexidine is probably one of the most sought-after substances for these functions.
Chlorhexidine is an odourless white crystalline powder. In cosmetics and personal care products, Chlorhexidine and its salts (Chlorhexidine Dihydrochloride, Chlorhexidine Digluconate and Chlorhexidine Diacetate) are used as antimicrobials, oral hygiene actives and preservatives. Besides cosmetics, chlorhexidine is widely used in medical practice. These ingredients, particularly the digluconate salt, are extensively used in dentistry because they inhibit plaque formation.
Antimicrobial action
As a cationic compound, Chlorhexidine interacts with the negatively charged bacterial cell membrane. Its bactericidal effect is linked to inhibition of membrane functions such as electron transfer and membrane-bound ATPase activity. Chlorhexidine is effective against a broad variety of Gram-positive and Gram-negative bacteria at relatively low concentrations.
Toxicological profile of Chlorhexidine
As highlighted above, Chlorhexidine has long been used in various product categories. Over the years its toxicological profile has been investigated in numerous scientific studies performed both on animals and humans, and the available bibliography may be considered sufficient to identify the main toxicological endpoints.
Chlorhexidine has been found to be slightly toxic in oral and inhalation studies; it was not carcinogenic in a 2-year drinking water study; and at cosmetic use concentrations it did not prove irritating to eyes or skin.
Impurities
Revision No. 10 of the SCCS notes of guidance for cosmetic ingredients and their safety evaluation pays special attention to potentially toxic impurities in cosmetic products.
p-Chloroaniline is used as a component in the synthesis of chlorhexidine but it is also a degradation product of chlorhexidine diacetate and digluconate. It is regularly detected after prolonged storage. At low pH and high temperatures, degradation is accelerated.
Some rat studies have shown a carcinogenic potential for p-Chloroaniline, which is why certificates of analysis supplied with the raw material generally indicate the level of this impurity.
It is therefore important to follow supplier instructions regarding storage conditions and shelf life in order to avoid increased concentrations of p-Chloroaniline.
Conclusions
Chlorhexidine and its salts are regulated under Annex V / 42 of the Cosmetics Regulation (EC) No 1223/2009. On the basis of the available information, the European Regulation authorises the use of Chlorhexidine and its salts up to a maximum concentration of 0.3% in cosmetic products.
Ref: Final Report on the Safety Assessment of Chlorhexidine / Chlorhexidine Diacetate / Chlorhexidine Dihydrochloride / Chlorhexidine Digluconate https://journals.sagepub.com/doi/abs/10.3109/10915819309140642