Glycerin (Glycerine). Trivalent alcohol, hygroscopic. Glycerin is the trade name when the percentage of glycerol is 95%, but the names Glycerin and Glycerol are mostly used to identify the same product. In practice: the pure chemical component is called glycerol, while glycerine contains about 95% glycerol.

Raw materials used in production. 

Glycerin can be produced from various lipids (fats and oils), and it is also obtained as a byproduct in the production of biodiesel and soap.

Step-by-step summary of industrial production process.

• Extraction or Synthesis. Glycerin can be obtained from saponification of fats (soap-making process).
• Refining. Crude glycerin is purified through a process that includes distillation and treating with activated carbon to remove impurities.
• Distillation. To achieve USP-grade or food-grade glycerin, the product must be distilled.

It occurs as an odourless, colourless to brown viscous liquid. Insoluble in chloroform, ether, carbon disulphide, benzene, oil. Miscible with ethanol and water. Can absorb moisture from the air as well as other volatile chemicals such as hydrogen sulphide, hydrogen cyanide and sulphur dioxide.  

What it is used for and where it is used

There are approximately 1,600 applications for glycerol.

Food

Hygroscopic agent, emulsifier,  sweetener and solvent. 

Military

Preparation of nitroglycerine, an explosive. Anticorrosive agent

Pharmaceutical

Syrups, suppository ointments as humectant, lubricant. Inserted in medicinal tablets as a humectant and flow agent.

Cosmetics

Its water solubility, hygroscopicity and hydrophilicity characteristics give glycerine humectant and moisturising capacities that are of great importance in most topical cosmetic applications. It attracts water to the surface of the skin and in this way maintains the hydration of the stratum corneum. By improving skin texture, it acts as a skin barrier. In cleansers, shampoos and other cosmetic products, it is included in the formula with the aim of moisturising and softening the skin, preserving it from ageing or roughness. It is also used in toothpastes as a humectant and to protect gum and tooth tissue.

Classic glycerine acts in cosmetic formulations in a number of useful ways, which I list in alphabetical order.

Cosmetics - INCI Functions

• Denaturant. The ionic or polar molecules of this ingredient included in formulations that interact with protein groups, modulate the properties of the solution to suit specific needs.
• Hair conditioning agent. A large number of ingredients with specific purposes can co-exist in a hair shampoo: cleansers, conditioners, thickeners, mattifying 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, dispersing agents that may contain cationic surfactants, thickeners, emollients, polymers. The typology of hair conditioners includes: intensive conditioners, instant conditioners, thickening conditioners, drying conditioners.
• Humectant. Hygroscopic compound used to minimise water loss in the skin and to prevent it from drying out by facilitating faster and greater absorption of water into the stratum corneum of the epidermis.  The epidermis is the most superficial of the three layers that make up human skin (epidermis, dermis and hypodermis) and is the layer that maintains hydration in all three layers. In turn, the epidermis is composed of five layers: horny, the most superficial, granular, spinous, shiny, and basal. Humectants have the ability to retain the water they attract from the air in the stratum corneum and have the function of moisturising the skin. They are best used before emollients, which are oil-based.
• Oral care agent. This ingredient can be placed in the oral cavity to improve and/or maintain oral hygiene and health, to prevent or improve a disorder of the teeth, gums, mucous membrane.
• Fragrance. It plays a very important role in the formulation of cosmetic products as it allows perfume to be enhanced, masked or added to the final product, improving its commercial viability.  The consumer always expects to find a pleasant scent in a cosmetic product.
• Skin conditioning agent. It is the mainstay of topical skin treatment by 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.
• Skin protectant. It creates a protective barrier on the skin to defend it from harmful substances, irritants, allergens, pathogens that can cause various inflammatory conditions. These products can also improve the natural skin barrier and in most cases more than one is needed to achieve an effective result.
• Solvent. It is the substance for dissolving or dispersing surfactants, oils, dyes, flavourings, bactericidal preservatives in solution.
• Viscosity control agent. It controls and adapts viscosity to the required level for optimal chemical and physical stability of the product and dosage in gels, suspensions, emulsions, solutions. 

Textile industry

Finishing techniques, co-solvent, dispersant, moisture absorbent. Wetting agent, hygroscopic agent, anti-shrinkage treatment of fabrics.

Coatings

Alkyd resin (modified thermosetting polyester), polyester resin, epoxy resin and glycidyl ether. and also: papermaking, in leather, photography, metalworking, rubber, printing and dyeing, antifreeze in lubricants and the petroleum sector

For more information:

Glycerin studies

Typical optimal commercial product characteristics Glycerol

• Molecular Formula : C₃H₈O₃    CH2OH-CHOH-CH2OH
• Linear Formula : HOCH₂CH(OH)CH₂OH
• PMolecular Weight : 92.094 g/mol
• Exact Mass   92.047340
• CAS : 56-81-5   8043-29-6   25618-55-7   8013-25-0  
• UNII    PDC6A3C0OX
• EC Number: 200-289-5
• MDL number: MFCD00004722
• PubChem Substance ID: 24895216
• DSSTox Substance ID DTXSID9020663    DTXSID4020662
• IUPAC  propane-1,2,3-triol
• InChI=1S/C3H8O3/c4-1-3(6)2-5/h3-6H,1-2H2 
• InChl Key      PEDCQBHIVMGVHV-UHFFFAOYSA-N
• SMILES    C(C(CO)O)O
• ChEBI  17754
• ICSC    0624
• NSC   759633    9230
• RTECS   MA8050000 
• NCI C29077

Synonyms:

• Glycerin
• Glycerine
• Glycyl alcohol
• 1,2,3-trihydroxypropane
• 1,2,3-Propanetriol
• Synthetic glycerin
• Polyglycerine

Compendium of the most significant studies with reference to properties, intake, effects.

Becker LC, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler DC, Marks JG Jr, Shank RC, Slaga TJ, Snyder PW, Gill LJ, Heldreth B. Safety Assessment of Glycerin as Used in Cosmetics. Int J Toxicol. 2019 Nov/Dec;38(3_suppl):6S-22S. doi: 10.1177/1091581819883820. 

Abstract. This is a safety assessment of glycerin as used in cosmetics. Glycerin functions as a denaturant, fragrance ingredient, hair conditioning agent, humectant, oral care agent, oral health-care drug, skin protectant, skin conditioning agent-humectant, and viscosity-decreasing agent. The Cosmetic Ingredient Review Expert Panel (Panel) reviewed relevant animal and human data. The Panel concluded that glycerin is safe as a cosmetic ingredient in the practices of use and concentration described in this safety assessment.

Shinde S, Kabra NS, Sharma SR, Avasthi BS, Ahmed J. Glycerin suppository for promoting feeding tolerance in preterm very low birthweight neonates: a randomized controlled trial. Indian Pediatr. 2014 May;51(5):367-70. doi: 10.1007/s13312-014-0418-8.

Abstract. Objective: To compare the efficacy of glycerin suppository versus no suppository in preterm very-low-birthweight neonates for improving feeding tolerance....Conclusions: Once daily application of glycerin suppository does not accelerate the achievement of full feeds in preterm very-low-birthweight neonates.

Daehnhardt-Pfeiffer S, Surber C, Wilhelm KP, Daehnhardt D, Springmann G, Boettcher M, Foelster-Holst R. Noninvasive stratum corneum sampling and electron microscopical examination of skin barrier integrity: pilot study with a topical glycerin formulation for atopic dermatitis. Skin Pharmacol Physiol. 2012;25(3):155-61. doi: 10.1159/000336789.

Abstract. Introduction: Therapy of atopic dermatitis encloses use of medicated and nonmedicated preparations. Results of clinical and biophysical procedures indirectly describe the condition of the impaired skin barrier (SB). Direct evaluation of SB integrity is only possible by electron microscopical visualization, e.g. intercellular lipid lamellae (ICLL) organization of the stratum corneum.....Conclusions: The study reveals that morphometric analysis of ICLL organization is suitable to differentiate between healthy and diseased skin and to semiquantitatively determine the effect of a nonmedicated glycerin formulation. Copyright © 2012 S. Karger AG, Basel.

Hanada K, Okuda D, Ogi R, Kojima S, Tsuruoka R, Shiota G. Ozonized glycerin (OG)-based cosmetic products lighten age spots on human facial skin. J Cosmet Dermatol. 2022 Jul;21(7):3133-3139. doi: 10.1111/jocd.15002. 

Abstract. Background: Few cosmetic ingredients are shown to be able to safely remove or lighten facial dark spots once they have formed. OG has been reported to possess oxidation power and exhibit various biological activities such as antibacterial, antiviral, and wound healing promotion. Aims: This study aimed to clarify the effects of OG on human skin, especially on age spots on the face....Conclusion: The result indicated that applications of OG formulations are safe and effective in lightening age spots on the facial skin. © 2022 The Authors. Journal of Cosmetic Dermatology published by Wiley Periodicals LLC.

Aoshima H, Miyagisnima A, Nozawa Y, Sadzuka Y, Sonobe T. Glycerin fatty acid esters as a new lubricant of tablets. Int J Pharm. 2005 Apr 11;293(1-2):25-34. doi: 10.1016/j.ijpharm.2004.12.007. 

Abstract. Lubrication properties were compared among glycerin fatty acid esters (Poem TR-FB and Poem TR-HB), magnesium stearate (Mg-St), and a sucrose fatty acid ester (RYOTO SUGAR ESTER S-370F: SSE). Granules containing 50% acetaminophen were prepared, and improvements in their fluidity by the lubricants were compared.  The lubricant effects of TR-FB and HB during tablet punching (pressure transmission ratio, ejection force) were similar to those of Mg-St and were better than those of SSE. When the lubricant content, mixing time, and tabletting pressure were changed, TR-FB and TR-HB provided better tablet hardness than Mg-St. TR-FB and TR-HB made tablets more disintegratable than Mg-St. When the effects of these lubricants on the stability of acetylsalicylic acid (ASA) were compared, Mg-St promoted its hydrolysis, but TR-FB or TR-HB did not affect its stability.

Burns J, Stephens M. Palliative wound management: the use of a glycerine hydrogel. Br J Nurs. 2003 Mar;12(6 Suppl):S14-8. doi: 10.12968/bjon.2003.12.Sup1.11248. 

Abstract. This article describes the use of a topical glycerine hydrogel and the role it can play in the management of malignant fungating wounds. The value of the product is reviewed in two case studies. The authors accept that no significant statistical evidence can be offered from the case studies, but highlight the benefit of the product to the patient's quality of life.

Stout EI, McKessor A. Glycerin-Based Hydrogel for Infection Control. Adv Wound Care (New Rochelle). 2012 Feb;1(1):48-51. doi: 10.1089/wound.2011.0288. 

Abstract. Problem: Infection is a major problem in the health and wellbeing of patients in hospitals, nursing homes, and other medical facilities as well as the homecare patients and the general public. According to Scientia Advisors, wound care costs the healthcare system over $7 billion in 2009. After adding the cost associated with potential complications such as infections, extended physician care, and lengthy hospital stays, the annual wound care expenditures well exceeded over $20 billion.1 There are 20 million reported cases of diabetes per year and more every day. Because of the fact that leg ulcers are the number one health problem of men coupled with the rise in drug resistance of infections, the importance of providing the professional and the public with relatively simple and affordable wound care is of extreme importance. Often the wounds can become chronic wounds, which then result in long-term nursing expense in time and supplies or, worse yet, can result in expensive amputations ranging from $5000 to $40,000 per patient......Indications for use: Elasto-Gel™ has been approved for all types of wounds, that is, pressure ulcers, acute and chronic wounds, diabetic wounds, traumatic wounds, dermatology wounds, cancer tumors, and first- and second-degree burns, to name a few. Because of the product's features and benefits, it may be used on a variety of wounds. Because of its padding properties, it may be also used as a preventative product over bony prominence areas so that wounds do not occur. The glycerin properties act as a skin substitute and may also be used for scar reduction. Caution: Elasto-Gel™ is not approved for third-degree burns as no dressing has been approved by the FDA for this type of wound.

Fluhr JW, Darlenski R, Surber C. Glycerol and the skin: holistic approach to its origin and functions. Br J Dermatol. 2008 Jul;159(1):23-34. doi: 10.1111/j.1365-2133.2008.08643.x.

Abstract. Glycerol is a trihydroxy alcohol that has been included for many years in topical dermatological preparations. In addition, endogenous glycerol plays a role in skin hydration, cutaneous elasticity and epidermal barrier repair. The aquaporin-3 transport channel and lipid metabolism in the pilosebaceous unit have been evidenced as potential pathways for endogenous delivery of glycerol and for its metabolism in the skin. Multiple effects of glycerol on the skin have been reported. The diverse actions of the polyol glycerol on the epidermis include improvement of stratum corneum hydration, skin barrier function and skin mechanical properties, inhibition of the stratum corneum lipid phase transition, protection against irritating stimuli, enhancement of desmosomal degradation, and acceleration of wound-healing processes. Even an antimicrobial effect has been demonstrated. Topical application of glycerol-containing products improves skin properties in diseases characterized by xerosis and impaired epidermal barrier function, such as atopic dermatitis. The increase of epidermal hydration by glycerol is critical in skin conditions aggravated by dry and cold environmental conditions, e.g. winter xerosis. This paper provides a review on effects of glycerol on the skin, the mechanisms of its action, and the potential applications of glycerol in dermatology.