At a Glance
- Propylene glycol (C₃H₈O₂) is a diol with two hydroxyl groups that create amphiphilic properties
- Functions primarily as co-emulsifier and emulsion stabilizer, not a standalone emulsifier
- GRAS status from FDA for food use; E1520 designation in Europe
- Typical use levels: 1-5% in cosmetics, up to 25% in pharmaceuticals
- Helps distribute oil and water phases but requires primary emulsifiers for stability
- Works by reducing interfacial tension and increasing miscibility between phases
- Applications span food, pharmaceuticals, cosmetics, and industrial formulations
- Derivatives like propylene glycol monostearate show stronger emulsifying properties
Most people know propylene glycol from reading ingredient labels on food or cosmetic products. But there’s ongoing confusion about what this compound actually does in formulations. Is propylene glycol an emulsifier? The answer isn’t as straightforward as you might expect. It can act as an emulsifier in cosmetic and pharmaceutical creams, as a solvent in elixirs and other liquid medications, or as a plasticizer in hair sprays, hand sanitizers, and moisturizing creams.
By emulsifying the active ingredients, which otherwise would not mix, the propylene glycol creates a stable homogeneous fluid that will allow the intended final product, be it a face cream or shampoo, for example, to do its job. However, calling propylene glycol a propylene glycol emulsifying agent requires some clarification. It functions more accurately as a co-emulsifier or emulsion stabilizer rather than a primary emulsifying agent.
Understanding Propylene Glycol’s Dual Nature
Propylene glycol is indeed a synthetic organic derivative which qualifies the diol nomenclature because of the presence of two hydroxyl (-OH) groups in it. It is a colorless, odorless, slightly viscous liquid sweet, mild in taste, highly hygroscopic, attracting, and holding vapor.
The two hydroxyl groups give propylene glycol its useful properties. One end of the molecule has some affinity for water (hydrophilic), while the carbon chain provides mild oil-affinity (lipophilic). This creates what chemists call an amphiphilic molecule.
Key Properties That Support Emulsification:
| Property | Value | Relevance to Emulsification |
| Molecular weight | 76.09 g/mol | Small size allows penetration between phases |
| Boiling point | 188.2°C | Stable under typical processing conditions |
| Viscosity | 40.4 mPa·s at 25°C | Slightly viscous, improves texture |
| Water solubility | Complete miscibility | Excellent water phase compatibility |
| Hygroscopic nature | Strongly absorbs moisture | Maintains hydration in formulations |
Because of its mutual solvent properties, both aromatic chemicals and essential oils can be dissolved in propylene glycol and then diluted with water. This mutual solvency makes propylene glycol valuable for bringing together ingredients that normally wouldn’t mix.
How Propylene Glycol Works in Emulsion Systems
Emulsions are mixtures of oil and water that normally separate. Creating stable emulsions requires interfering with that natural separation tendency. Traditional emulsifiers accomplish this by positioning themselves at the oil-water interface, with their hydrophilic end in water and lipophilic end in oil.
Propylene glycol works differently. Propylene glycol is often used as an emulsifier or aid in solubilizing other raw materials, such as parabens, fragrances, and vitamins. Notice the phrasing: “aid in solubilizing” rather than direct emulsification.
Propylene Glycol’s Emulsion Support Mechanisms:
Interfacial tension reduction: The molecule’s dual affinity reduces the energy barrier between oil and water phases. This makes it easier for primary emulsifiers to do their job.
Co-solvent action: Propylene glycol dissolves compounds that have intermediate polarity. These compounds might not dissolve well in pure water or pure oil, but propylene glycol bridges that gap.
Viscosity modification: Its slightly viscous nature slows droplet movement and coalescence. This mechanical effect supports emulsion stability even without strong interfacial activity.
Moisture retention: The hygroscopic nature keeps water evenly distributed throughout the formulation. This prevents localized drying that could destabilize emulsions.
Propylene Glycol Derivatives: Enhanced Emulsifying Properties
While propylene glycol itself shows limited emulsifying capability, its derivatives can be powerful emulsifiers. Propylene Glycol Monooleate (PGMO), CAS 1330-80-9, is a versatile ester derived from propylene glycol and oleic acid. Renowned for its amphiphilic nature, it excels as an emulsifier, surfactant, moisturizer, and stabilizer across diverse industries including food, pharmaceuticals, and cosmetics.
Common Propylene Glycol-Based Emulsifiers:
- Propylene glycol monostearate: Oil-in-water emulsifier for foods and cosmetics
- Propylene glycol monolaurate: Antimicrobial and emulsifying properties
- Propylene glycol monooleate: Soft emulsifier for pharmaceutical creams
- Propylene glycol alginate (E405): Stabilizes proteins under acidic conditions
The ester derivatives of polyhydric alcohols and fatty acids belong to the group of nonionic surface active agents which are commonly used in the pharmaceutical, cosmetic and food industries as water-in-oil (W/O) emulsion stabilizers.
These derivatives have longer hydrocarbon chains from the fatty acid portion, giving them much stronger interfacial activity than propylene glycol alone. They can serve as primary emulsifiers rather than just co-emulsifiers.
Food Industry Applications
In regulated amounts, propylene glycol is designated as safe for food manufacturing as an anticaking agent, emulsifier, flavor agent, humectant, texturizer, stabilizer, solvent, antioxidant, antimicrobial agent, and thickener.
Beverage Stabilization
In soft drinks, it is employed as a syrup flavor solvent and imparts smoothness, body and sparkle to the final product. Propylene glycol helps keep flavor oils dispersed in beverages. Without it, essential oils would float to the surface or create visible droplets.
Salad Dressings and Emulsions
As an emulsifier, it is used to prevent ingredients such as oil and vinegar in salad dressing from separating. However, salad dressings also contain primary emulsifiers like egg yolk or mustard. Propylene glycol supports but doesn’t replace these traditional emulsifiers.
Dairy and Frozen Desserts
Health Canada permits use of propylene glycol mono fatty acid esters as an emulsifier and stabilizer at a maximum level of use of 0.35% of the ice cream made from the ingredients mix. Note this regulation refers to the fatty acid ester derivatives, not propylene glycol itself.
In ice cream, propylene glycol and its esters:
- Improve texture and prevent ice crystal formation
- Help distribute flavors evenly
- Stabilize air incorporation
- Extend shelf life by preventing separation
Pharmaceutical Formulations
Propylene glycol is used in a wide variety of pharmaceutical formulations and is generally regarded as a relatively nontoxic material. Its versatility makes it valuable across different dosage forms.
Injectable Medications
Propylene glycol serves as a co-solvent in injectable formulations where drugs don’t dissolve well in water alone. Drugs like lorazepam and diazepam use high concentrations of propylene glycol to stay dissolved. While the emulsifying function isn’t primary in these solutions, propylene glycol does help when lipophilic drugs need to be administered in aqueous environments.
Topical Creams and Ointments
The compositions contain mometasone in micronised form, propylene glycol and water and the weight ratio between the propylene glycol and water contained in the oil-in-water emulsion is from 1:1 to about 1:3.
In pharmaceutical creams, propylene glycol:
- Enhances drug penetration through skin
- Improves spreadability and feel
- Prevents microbial growth
- Stabilizes emulsions against phase separation
- Serves as a humectant maintaining moisture
Oral Suspensions and Syrups
Propylene glycol is also used in cosmetics and in the food industry as a carrier for emulsifiers and as a vehicle for flavors in preference to ethanol, since its lack of volatility provides a more uniform flavor.
The non-volatile nature means flavors don’t evaporate during storage. This maintains consistent taste throughout the product’s shelf life.
Cosmetic and Personal Care Products
Propylene glycol improves the texture and stability of formulations. It is used in many pharmaceuticals, skincare products, and decorative cosmetics.
Skin Care Formulations
Lotions, creams, and serums use propylene glycol at 1-5% concentration. Higher levels up to 10% appear in some specialized products. In some cases, concentration can reach up to 10%, but it is still safe as propylene glycol can be used in cosmetics in concentrations up to 50%.
Functions in skincare:
- Co-emulsifier supporting primary emulsifying systems
- Humectant drawing moisture to skin
- Penetration enhancer for active ingredients
- Texture modifier creating light, non-greasy feel
- Preservative booster extending antimicrobial effectiveness
Hair Care Products
Shampoos and conditioners incorporate propylene glycol to:
- Improve product consistency
- Enhance spreadability through hair
- Maintain moisture balance
- Stabilize fragrances and active ingredients
- Prevent ingredient separation during storage
Makeup and Color Cosmetics
Foundation, mascara, and other color cosmetics benefit from propylene glycol’s ability to:
- Keep pigments evenly dispersed
- Prevent caking and clumping
- Maintain smooth texture
- Improve application properties
- Extend product usability
Industrial and Technical Applications
Beyond consumer products, propylene glycol supports emulsion systems in industrial settings.
Paint and Coating Formulations
Propylene glycol’s high boiling point, dye solvency and strong penetrating properties make it an ideal ingredient for the formulation of high speed steam-set inks.
In paints and coatings:
- Helps disperse pigments uniformly
- Prevents settling during storage
- Controls viscosity
- Improves film formation
- Reduces coalescence time
Metalworking Fluids
Cutting fluids and coolants use propylene glycol to:
- Emulsify lubricating oils with water
- Improve heat transfer properties
- Prevent microbial growth
- Stabilize pH
- Extend fluid life
Limitations as a Standalone Emulsifier
Propylene glycol alone cannot create stable emulsions in most applications. In order to stabilize the emulsion against phase separation, surface active ingredients known as emulsifying agents are required.
Typical emulsion formulations combine:
- Primary emulsifier (lecithin, polysorbates, fatty acid esters)
- Co-emulsifier (propylene glycol, glycerin)
- Thickening agents (xanthan gum, cellulose derivatives)
- Stabilizers (fatty alcohols)
Propylene glycol enhances the system but doesn’t replace traditional emulsifying agents. Formulators who try using propylene glycol as the sole emulsifier typically end up with unstable products that separate quickly.
Safety and Regulatory Status
The European Food Safety Authority authorizes propylene glycol for use in food manufacturing, establishing a safe daily intake of 25 mg per kg of body weight. This translates to about 1,500 mg daily for a 60 kg adult.
On the basis of metabolic and toxicological data, the WHO has set an acceptable daily intake of propylene glycol at up to 25 mg/kg body-weight.
The compound is rapidly metabolized to lactic acid and pyruvic acid, normal metabolites in the body. This metabolic pathway explains its relatively low toxicity compared to other glycols.
Sourcing Quality Propylene Glycol
For manufacturers formulating food products, pharmaceuticals, cosmetics, or industrial applications requiring propylene glycol, partnering with suppliers who understand both the chemical industry and specific application requirements makes a difference. Elchemy leverages technology to transform how businesses source chemicals globally. Founded by chemical and electronics engineers from IIT Bombay, IIT Delhi, and IIM Ahmedabad, Elchemy connects manufacturers with verified suppliers of propylene glycol meeting USP, FCC, and industrial specifications.
Whether you need pharmaceutical-grade propylene glycol for injectable formulations, food-grade for beverage production, or technical-grade for industrial emulsion systems, Elchemy’s technology-driven platform streamlines sourcing from both Indian and global suppliers. Our customer-centric approach addresses the operational challenges manufacturers face, providing transparent supply chain solutions, quality documentation, and efficient logistics that traditional chemical distribution struggles to deliver.
Conclusion
Propylene glycol functions as an emulsifying agent in the broadest sense, but more accurately serves as a co-emulsifier and emulsion stabilizer. Its dual water-oil affinity, moisture retention capability, and ability to solubilize intermediate polarity compounds make it valuable across food, pharmaceutical, cosmetic, and industrial formulations.
However, successful emulsion systems typically require combining propylene glycol with traditional emulsifiers rather than relying on it alone. Understanding this distinction helps formulators design stable products while leveraging propylene glycol’s multiple functional benefits beyond simple emulsification.
