Among the many glycols used in modern industry, monopropylene glycol (MPG) and dipropylene glycol (DPG) stand out for their roles in pharmaceutical and food applications. Safe, versatile, and tightly regulated, these glycols are valued as solvents, humectants, carriers, and stabilisers. Yet, their very ubiquity demands vigilance – particularly around contamination risks with toxic ethylene glycol.
This post explores their history, production, applications, safety considerations, and what the future holds for these critical ingredients.
A Brief History of Glycols
The history of glycols traces back to the early 19th century, when chemists first began to explore alcohol derivatives from petroleum sources. Propylene glycol (PG) was first produced in the early 20th century as a safer alternative to ethylene glycol (EG), which, despite its effectiveness as an antifreeze, is toxic to humans.
- Monopropylene glycol (MPG) – also called propylene glycol (PG) – emerged as a food-safe, pharmaceutical-safe glycol with wide adoption in the 1930s.
- Dipropylene glycol (DPG) was developed as a by-product of MPG production, offering different solubility and viscosity characteristics that made it useful in cosmetics, fragrances, and certain drug formulations.
The key breakthrough was demonstrating safety for ingestion and topical use, which allowed MPG and later DPG to become excipients and food additives – unlike ethylene glycol, which remains strictly industrial.
Modern Production Methods
Both MPG and DPG are produced primarily from propylene oxide, itself derived from petroleum or increasingly from bio-based propylene.
- Hydration of propylene oxide – Propylene oxide is reacted with water, yielding a mixture of monopropylene glycol and small amounts of dipropylene glycol and tripropylene glycol.
- Separation & Purification – Fractional distillation separates MPG and DPG into distinct products.
- Grades –
- Industrial grades (for antifreeze, coatings, resins)
- USP/Ph.Eur./Food grades (for pharmaceuticals, food, cosmetics, e-liquids)
For pharma and food use, rigorous purification ensures compliance with pharmacopoeial standards (USP, Ph. Eur., JP) and food additive regulations (E1520 in the EU).
Uses in Pharmaceuticals
Monopropylene glycol (MPG) is one of the most widely used pharmaceutical excipients:
- Solvent – for APIs with low solubility in water, enabling stable liquid formulations.
- Carrier & Stabiliser – in oral, injectable, and topical products.
- Humectant – maintaining moisture balance in creams, ointments, and gels.
- Preservative synergy – enhances antimicrobial activity when used alongside preservatives.
Dipropylene glycol (DPG), though less common, is employed where different solubility and viscosity are beneficial:
- Solvent in injectables and topical medicines
- Carrier in controlled-release formulations
- Stabiliser in sensitive actives
Uses in Food and Flavourings
MPG is also authorised as a food additive (E1520), with roles including:
- Solvent – dissolving flavourings, colours, and emulsifiers.
- Humectant – keeping foods and baked goods moist.
- Carrier – stabilising food extracts, vanilla, and essential oils.
DPG is less widely used in foods, but is important in:
- Fragrances and flavour formulations where its low volatility and mild odour help deliver consistency.
- Food contact materials, including inks and coatings used in packaging.
Safety Considerations: Avoiding Ethylene Glycol Contamination
The greatest safety risk associated with MPG and DPG is ethylene glycol (EG) contamination. EG is chemically similar but highly toxic, and its accidental substitution or contamination has led to serious poisoning incidents in pharmaceutical syrups and food products.
Regulatory authorities (EMA, FDA, WHO) mandate:
- Strict GMP controls in glycol production.
- Analytical testing to detect trace EG or diethylene glycol (DEG).
- Supplier qualification and traceability as part of pharmaceutical quality systems.
The 2006 Panama diethylene glycol tragedy and similar events in Bangladesh and Nigeria underline why sourcing from reputable, GMP-certified suppliers is non-negotiable.
Future Trends: What’s Next for MPG & DPG?
Several trends are shaping the future of glycols in pharma and food:
- Bio-based propylene glycol – Demand for renewable, low-carbon glycols is rising, produced from glycerol or bio-propane rather than petroleum.
- Stricter regulations on contaminants – More stringent global pharmacopoeial requirements for EG/DEG testing are now in place.
- Expansion in nutraceuticals and e-liquids – MPG continues to be widely used in vaping liquids and nutraceuticals, increasing demand for high-purity, food-safe grades.
- Growth in personal care – Both MPG and DPG are expanding in cosmetics as humectants and fragrance carriers, driven by consumer demand for multifunctional ingredients.
Conclusion
Monopropylene glycol and dipropylene glycol are more than just commodity chemicals – they are critical enablers of safe and effective medicines, foods, and personal care products. Their value lies in versatility, safety, and functionality, but only when sourced from reliable, GMP- and food-grade suppliers with robust controls against ethylene glycol contamination.
As sustainability pressures mount, bio-based glycols and tighter supply chain oversight will define the next era of glycol sourcing. For pharmaceutical and food manufacturers, ensuring glycol quality isn’t just compliance – it is central to consumer safety and brand trust.
Looking for a trusted supply of pharmaceutical- and food-grade glycols? Contact Kimia to learn more about our range of certified MPG and DPG solutions.