Propylene Glycol (PG): A Versatile Solvent and Humectant

Technical Introduction

Propylene Glycol (PG) is a synthetic organic compound belonging to the alcohol (diol) family. It is a clear, colorless, odorless, slightly viscous liquid with a faintly sweet taste. Because of its hygroscopic nature, miscibility with water and many organic solvents, and low toxicity, it is widely used in pharmaceutical, food, cosmetic, and industrial formulations.

• Chemical Name: 1,2-Propanediol

• Synonyms: PG, Propane-1,2-diol

• CAS Number: 57-55-6

• Molecular Formula: C₃H₈O₂

• Molecular Weight: 76.09 g/mol

• Appearance: Colorless, odorless, viscous liquid

• Solubility: Miscible with water, acetone, chloroform, ethanol

• Nature: Humectant, solvent, stabilizer

Applications

1. Pharmaceuticals & Medicine

• Used as a solvent, stabilizer, and excipient in oral, injectable, and topical medicines.

• Acts as a carrier for active ingredients in formulations.

• Used in antiseptics, cough syrups, creams, and injectable drugs.

2. Food & Beverages

• Approved as a food additive (E1520) for use as a solvent, humectant, and preservative.

• Enhances moisture retention in baked goods, candies, and processed foods.

• Used as a carrier for flavors, colors, and emulsifiers.

3. Cosmetics & Personal Care

• Found in lotions, creams, shampoos, deodorants, and toothpaste.

• Provides moisturization and improves spreadability of formulations.

4. Industrial Applications

• Used as a coolant, antifreeze, and de-icing fluid (safer alternative to ethylene glycol).

• Plays a role in plasticizer and resin formulations.

• Employed in electronic cigarettes (e-liquids) as a carrier base.

✅ Advantages

• Safe and low-toxicity compared to ethylene glycol.

• Excellent solvent for both hydrophilic and hydrophobic substances.

• Strong humectant properties, helps retain moisture.

• Stable under heat and light, making it suitable for processing.

• Versatile usage across pharmaceuticals, foods, cosmetics, and industry.

• Environmentally safer due to biodegradability.

⚙️ Technical Specifications (Typical Parameters)

⚠️ Safety & Regulations

• Generally Recognized as Safe (GRAS) by the FDA for food and pharmaceutical use.

• Acceptable Daily Intake (ADI): Up to 25 mg/kg body weight (as per WHO/FAO).

• Toxicity: Very low; large amounts may cause gastrointestinal upset.

• Skin & Eye Contact: Generally safe; rarely may cause mild irritation in sensitive individuals.

• Environmental Impact: Readily biodegradable and less hazardous than ethylene glycol.

❓ FAQ

Q1: Is propylene glycol the same as ethylene glycol?
No. Unlike ethylene glycol, which is toxic, propylene glycol is low-toxicity and safe for regulated uses in food, medicine, and cosmetics.

Q2: Why is propylene glycol used in e-liquids?
It serves as a carrier for nicotine and flavors and produces the "throat hit" sensation preferred by many users.

Q3: Is propylene glycol safe for sensitive skin?
Yes, but some individuals with very sensitive skin may experience mild irritation. Cosmetic-grade PG is purified to minimize this risk.

Q4: Can propylene glycol be used as antifreeze?
Yes. It is a safer alternative to ethylene glycol antifreeze, especially in food-related or environmentally sensitive applications.

Q5: Is propylene glycol natural or synthetic?
It is synthetically produced by hydration of propylene oxide but is considered safe due to its low toxicity and biodegradability.