Glycols
Glycols are dihydric alcohols derived from ethylene glycol, meaning they are closely related to classic drinking alcohol. They are often used in de-icers, coolants and antifreeze agents, as their freezing point is between minus 10.0 and minus 15.0 degrees Celsius. When combined with water, the freezing point is even lower, reaching values of up to minus 55 degrees Celsius, depending on the mixture. Chemical differences from other alcohols can be seen primarily in the number of alcoholic hydroxy groups. Alcohol (ethanol) has one OH group, while ethylene glycol (ethanediol) has two OH groups. Longer-chain glycols such as butylene glycol, pentylene glycol, propylene glycol and hexylene glycol are structured in a similar way. Glycols are generally characterised by a sweet taste, which is already evident from their name. The name comes from Greek and translates as ‘sweet’.
Glycols and their properties and advantages
Microbial activity is inhibited when the minimum inhibitory concentration (MIC) is reached. This is a very typical property of glycols. The situation is very similar with drinking alcohol: during the alcoholic fermentation of grape juice into wine, the yeasts die off once a certain alcohol concentration is reached.
Glycols are therefore very popular as alcohol substitutes to improve the shelf life of cosmetics, especially since, unlike alcohol, they are not volatile. Regularly opening an aqueous-alcoholic cosmetic product would cause the MIC to fall below the minimum level, resulting in microbiological instability. The product would therefore spoil. In addition, alcohol has a strong odour of its own, which is undesirable in cosmetics.
However, ethylene glycol is very rarely used in the manufacture of personal care products. For example, oxalic acid, the main metabolite of ethylene glycol in the human body, is known to be harmful to the kidneys and is therefore only permitted in hair treatment products at a maximum concentration of 5.0 per cent.
Glycols in cosmetic products
Glycols such as propylene glycol, butylene glycol and pentylene glycol attract water and bind moisture, meaning they are hygroscopic. Cosmetic products containing such glycols are able to improve skin moisture. The skin’s own glycerine, which is related to these substances, has a particularly pronounced water-binding effect. High-dose glycerine creams have an excellent moisturising effect, but most of the glycerine is later washed out during washing and showering, leaving the skin feeling relatively dry. However, this effect can be neutralised by increasing the lipid concentration and simultaneously reducing the glycerine content.
Propylene glycol is used particularly frequently. A few years ago, these glycols were mistakenly associated with allergic reactions, but these were due to impurities. A comprehensive study by the Dermatology Clinic at the University of Karlsruhe proved that propylene glycol does not pose a sensitisation risk despite intensive use at high purity. Propylene glycol is also approved as a food additive (E 1520).
The innovation: sustainably produced glycols
More and more manufacturers are switching to producing glycols in a natural and sustainable way. One example is dermosoft(R) Pentiol eco, a natural and sustainable grade of pentylene glycol. This multifunctional additive is pH-independent, water-soluble and liquid, and has little effect on emulsion stability.
dermosoft(R) Pentiol eco profile
INCI: Pentylene Glycol
CAS number: 5343-92-0
Areas of application: for face, body, hand and foot care, deodorants and decorative cosmetics
Dosage: 1.0 to 5.0 per cent
Another example of natural glycols is Zemea, a natural propylene glycol obtained from corn sugar fermentation. It is already considered the optimal alternative to mineral oil-based glycols such as butylene and propylene glycol or glycerine. Zemea is produced from renewable raw materials and serves as a ‘preservative booster’, as its addition reduces the usual concentration of preservatives by around half without compromising performance.
Zemea profile
INCI: Propanediol
Appearance: colourless and clear
Origin: obtained from renewable raw materials (corn), ECOCERT-certified
Properties: very good skin compatibility, preservative booster, significant reduction in the concentration of preservatives used.
Genomatica, the widely recognised technology leader in chemicals, has also launched a natural Brontide(TM) butylene glycol. Butylene glycol is also used in a variety of personal care products and, as a humectant, increases moisture retention. These glycols also improve texture and have antimicrobial properties.
Basically, these naturally produced glycols are always a better choice for high-quality (natural) cosmetics.
Profiles of the most well-known glycols
1,2-Propanediol
INCI: Propylene glycol
CAS number: 57-55-6
Properties: clear, odourless, colourless, hygroscopic, liquid
Uses: as a humectant in deodorants, skin creams, toothpaste and mouthwashes, carrier and carrier solvent for flavours, antioxidants, colourants and enzymes, food additive for chewing gum and food supplements E 1520
1,3-butanediol
INCI: butylene glycol
CAS number: 107-88-0
Properties: skin care, moisturising, masking, viscosity control
Areas of application: preservative in various cosmetic products such as body lotions and hair care products
1,2-pentanediol
INCI: Pentylene glycol
CAS number: 5343-92-0
Properties: colourless, viscous, water-soluble liquid
Effect: moisturising, antimicrobial, as a solubiliser
2,4-Dihydroxy-2-methylpentane
INCI: Hexylene glycol
CAS number: 107-41-5
Properties: emulsifying, skin-conditioning,
Areas of application: in hand creams and aftershave, as a glycerol substitute in O/W emulsions, among other things
1,2-octanediol
INCI: caprylyl glycol
CAS number: 1117-86-8
Areas of application: for hair conditioning, as a humectant, for skin care
1,2-Decanediol
INCI: Decylene Glycol
CAS number: 1119-86-4
Appearance: white waxy solid
Effect: antimicrobial properties, moisturising, suitable for many personal care applications
Glycols in cosmetics
Glycols are virtually indispensable as auxiliary and active ingredients in decorative cosmetics, skin care products and dermatologicals due to their properties. Today, sustainable natural solutions are available that offer excellent tolerability.
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