Caprylyl glycol  is a chemical compound, 1,2-glycol produced by synthetic hot oxidation through water of Caprylyl alcohol obtained from plant extraction, coconut.

The name describes the structure of the molecule:

• Caprylyl refers to caprylic acid, a medium-chain fatty acid. In the context of this compound, "caprylyl" indicates a derivative of caprylic acid.
• glycol refers to a group of chemical compounds that contain two alcohol groups. In caprylyl glycol, these alcohol groups are attached to the structure of caprylic acid.

Raw Materials and Their Functions

Glycol. An organic compound used as the base for the synthesis of caprylyl glycol. It contributes to the moisturizing properties of the final product.

Caprylic Acid. A medium-chain fatty acid derived from natural sources like coconut oil or palm oil, used in the synthesis of caprylyl glycol.

Industrial Chemical Synthesis of Caprylyl Glycol

• Esterification Reaction. The reaction of caprylic acid with glycol to form caprylyl glycol. This reaction involves the formation of an ester bond between the acid and the glycol.
• Reaction Control. The esterification reaction is monitored to ensure it occurs correctly and the final product has the desired properties.
• Purification. After the reaction, caprylyl glycol is purified to remove impurities and by-products.
• Quality Control. The purified caprylyl glycol undergoes quality checks to ensure it meets the required standards. After quality control, it is packaged for use in cosmetic and personal care products, where it utilizes its moisturizing and antimicrobial properties.

It appears in form of white powder.

What it is used for and where

Caprylyl glycol is used as a moisturizing and emollient agent in cosmetic products. It is also known for its antimicrobial properties and is often used either as a single preservative or to reinforce the effectiveness of other preservatives.

Cosmetics

Skin conditioning agent - Emollient. Emollients have the characteristic of enhancing the skin barrier through a source of exogenous lipids that adhere to the skin, improving barrier properties by filling gaps in intercorneocyte clusters to improve hydration while protecting against inflammation. In practice, they have the ability to create a barrier that prevents transepidermal water loss.  Emollients are described as degreasing or refreshing additives that improve the lipid content of the upper layers of the skin by preventing degreasing and drying of the skin. The problem with emollients is that many have a strong lipophilic character and are identified as occlusive ingredients; they are oily and fatty materials that remain on the skin surface and reduce transepidermal water loss. In cosmetics, emollients and moisturisers are often considered synonymous with humectants and occlusives.

Deodorant agent. When substances that give off an unpleasant odour are included in cosmetic formulations (typical examples are methyl mercaptan and hydrogen sulphide derived from garlic), deodorants attenuate or eliminate the unpleasant exhalation.  It helps counteract the formation of bad odours on body surfaces.

Skin conditioning agent. It is the mainstay of topical skin treatment as it has the function of restoring, increasing or improving skin tolerance to external factors, including melanocyte tolerance. The most important function of the conditioning agent is to prevent skin dehydration, but the subject is rather complex and involves emollients and humectants that can be added in the formulation.

Hair conditioning agent. A significant number of ingredients with specific and targeted purposes may co-exist in hair shampoo formulations: cleansers, conditioners, thickeners, matting agents, sequestering agents, fragrances, preservatives, special additives. However, the indispensable ingredients are the cleansers and conditioners as they are necessary and sufficient for hair cleansing and manageability. The others act as commercial and non-essential auxiliaries such as: appearance, fragrance, colouring, etc. Hair conditioning agents have the task of increasing shine, manageability and volume, and reducing static electricity, especially after treatments such as colouring, ironing, waving, drying and brushing. They are, in practice, dispersants that may contain cationic surfactants, thickeners, emollients, polymers. The typology of hair conditioning agents includes: intensive conditioners, instant conditioners, thickening conditioners, drying conditioners. They can perform their task generally accompanied by other different ingredients.

Safety

 From the data published so far, this ingredient does not appear to have any impurities that could exceed the safety threshold.

Studies

Caprylyl glycol  is used as a preservative in cosmetic products in creams and nanosuspensions as aqueous formulations. Due to its highly lipophilic qualities (it dissolves easily in fats and oils) it has the greatest influence on the stability of nanosuspensions. In practice, the more lipophilic the preservative, the greater the destabilizing effect (1).

Caprylyl glycol  also possesses broad-spectrum antimicrobial activity with a positive correlation between the antimicrobial activity of the preservative and emulsion droplet particle size in the range of 100-900 nm when the same mixture concentration is used in the same formulation. Emulsion droplet particle size has been shown to be a recently discovered factor affecting the preservation of cosmetic products (2).

As with almost all chemical compounds included in cosmetic products there is no shortage of cases of contact allergies (3).

The most relevant studies and their abstracts have been selected to explore this in more depth:

Caprylyl glycol studies

Molecular Formula: C₈H₁₈O₂

Linear Formula: CH₃(CH₂)₅CH(OH)CH₂OH

Molecular Weight: 146.23 g/mol

UNII: 00YIU5438U

CAS: 87720-90-9  1117-86-8

Synonyms:

• (2R)-octane-1,2-diol
• (R)-(+)-1,2-Octanediol
• (R)-1,2-octanediol
• (r)-octane-1,2-diol
• 1,2-Octanediol,(2R)-
• 1 2-Dihydroxyoctane
• 1 2-Octylene glycol
• 1,2-Dihydroxyoctane
• 1,2-Octanediol
• 1,2-Octylene glycol
• 1,2-octanodiol
• 7 8-Dihydroxyoctane
• AI3-13058
• Dermosoft Octiol
• LexGard O
• NSC 71546
• Octane- 1, 2- diol
• Octane-1,2-diol
• Sodiol ON-D
• SCHEMBL2974733
• CHEBI:37874
• CTK5F8932
• DTXSID40426386
• ZINC1696956
• LMFA05000548
• AKOS017343274
• AJ-30321
• CJ-28479
• DB-077090
• FT-0605125

References______________________________________________________________________

(1) Al Shaal L, Müller RH, Keck CM. Preserving hesperetin nanosuspensions for dermal application. Pharmazie. 2010 Feb;65(2):86-92.

(2) Fang B, Yu M, Zhang W, Wang F. A new alternative to cosmetics preservation and the effect of the particle size of the emulsion droplets on preservation efficacy. Int J Cosmet Sci. 2016 Oct;38(5):496-503. doi: 10.1111/ics.12317.

(3) Kreeshan FC, Williams JDL. Allergic contact dermatitis to caprylyl glycol: A novel "para-preservative" allergen. Contact Dermatitis. 2020 Nov;83(5):418-419. doi: 10.1111/cod.13628.

Coelho EQ, Wu SLC, Nunes RS, Reis VMS. Contact urticaria following the use of a cosmetic containing caprylyl glycol: A case report. Contact Dermatitis. 2019 Oct;81(4):308-309. doi: 10.1111/cod.13299.

Preservatives are added to cosmetics to protect the consumers from infections and prevent product spoilage. The concentration of preservatives should be kept as low as possible and this can be achieved by adding potentiating agents. The aim of the study was to investigate the mechanisms behind potentiation of the bactericidal effect of a commonly used preservative, 2-phenoxyethanol (PE), by the potentiating agent ethylhexylglycerin (EHG). Sub-lethal concentrations of EHG (0.075%) and PE (0.675%) in combination led to rapid killing of E. coli (> 5 log reduction of cfu after 30 min), leakage of cellular constituents, disruption of the energy metabolism, morphological deformities of cells and condensation of DNA. Used alone, EHG disrupted the membrane integrity even at low concentrations. In conclusion, sub-lethal concentrations of EHG potentiate the effect of PE through damage of the cell membrane integrity. Thus, adding EHG to PE in a 1:9 ratio has a similar effect on membrane damage and bacterial viability as doubling the concentration of PE. This study provides insight about the mechanism of action of a strong potentiating agent, EHG, which is commonly used in cosmetics together with PE. (1)

The synergistic performance of caprylyl glycol, phenethyl alcohol and glyceryl caprylate and the anti-microbial activity of their blend suggest that their combination is effective and exhibits broad-spectrum anti-microbial activity. Furthermore, the results show a positive correlation between the anti-microbial activity of the preservative and the particle size of the emulsion droplets in the range of 100-900 nm, when the same concentration of the blend is used in the same formulation. The particle size of the emulsion droplets is demonstrated to be a newly discovered factor that influences the preservation of cosmetic products (2).

Caprylyl glycol and related 1,2-glycols are used mostly as skin and hair conditioning agents and viscosity agents in cosmetic products, and caprylyl glycol and pentylene glycol also function as cosmetic preservatives. The Cosmetic Ingredient Review (CIR) Expert Panel noted that, while these ingredients are dermally absorbed, modeling data predicted decreased skin penetration of longer chain 1,2-glycols. Because the negative oral toxicity data on shorter chain 1,2-glycols and genotoxicity data support the safety of the 1,2-glycols reviewed in this safety assessment, the Panel concluded that these ingredients are safe in the present practices of use and concentration described in this safety assessment (3).

Nanosuspensions as aqueous formulations need to be preserved. However, preservatives could vitiate the physical stability of suspensions and to a greater extent nanosuspensions. The impact of six varied preservatives on the physical stability of previously prepared nanosuspensions was studied. The hesperetin nanosuspensions were stabilized using plantacare 2000.30 cycles of high pressure homogenization (HPH) led to a mean photon correlation spectroscopy (PCS) diameter of 335 nm. The preservatives were, caprylyl glycol, Euxyl PE9010, Hydrolite-5, MultiEx naturotics, Phenonip and Rokonsal PB5. On one hand, aggregations were noticed after adding caprylyl glycol, MultiEx naturotics and Phenonip reaching PCS mean diameters of about 500, 1070, 800 nm, respectively. While on the other hand Euxyl PE9010, Hydrolite-5 and Rokonsal PB5 have not significantly affected the physical stability of the nanosuspensions with mean PCS diameters of about 365, 332, 350 nm, respectively. The obtained nanosuspensions were further characterized by measuring zeta potential. From the obtained data it was found that the lipophilicity of the used preservatives demonstrates major influence on the stability of the nanosuspensions, i.e. the higher lipophilicity of the preservative, the stronger the destabilizing effect. Briefly, highly hydrophilic preservatives are recommended to preserve hesperetin nanosuspensions in order to maintain their physical stability during storage (4).

Other studies

Contact urticaria following the use of a cosmetic containing caprylyl glycol: A case report.
Coelho EQ, Wu SLC, Nunes RS, Reis VMS.
Contact Dermatitis. 2019 Apr 26. doi: 10.1111/cod.13299.

Determination of alternative preservatives in cosmetic products by chromophoric derivatization followed by vortex-assisted liquid-liquid semimicroextraction and liquid chromatography.
Miralles P, Vrouvaki I, Chisvert A, Salvador A.
Talanta. 2016 Jul 1;154:1-6. doi: 10.1016/j.talanta.2016.03.033.

A new alternative to cosmetics preservation and the effect of the particle size of the emulsion droplets on preservation efficacy.
Fang B, Yu M, Zhang W, Wang F.
Int J Cosmet Sci. 2016 Oct;38(5):496-503. doi: 10.1111/ics.12317.

References____________________________________

(1)  Ethylhexylglycerin Impairs Membrane Integrity and Enhances the Lethal Effect of Phenoxyethanol  Solveig Langsrud, Katrin Steinhauer, Sonja Lüthje, Klaus Weber, Peter Goroncy-Bermes, Askild L. Holck  PLoS One. 2016 Oct 26;11(10):e0165228. doi: 10.1371/journal.pone.0165228.

(2) A new alternative to cosmetics preservation and the effect of the particle size of the emulsion droplets on preservation efficacy.
Fang B, Yu M, Zhang W, Wang F.
Int J Cosmet Sci. 2016 Oct;38(5):496-503. doi: 10.1111/ics.12317.

(3) Safety assessment of 1,2-glycols as used in cosmetics.
Johnson W Jr, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler D, Marks JG Jr, Shank RC, Slaga TJ, Snyder PW, Andersen FA.
Int J Toxicol. 2012 Sep-Oct;31(5 Suppl):147S-68S. doi: 10.1177/1091581812460409.

(4) Preserving hesperetin nanosuspensions for dermal application.
Al Shaal L, Müller RH, Keck CM.
Pharmazie. 2010 Feb;65(2):86-92.