What Is Propylene Glycol?
Propylene glycol (PG), also called 1,2-propanediol or monopropylene glycol (MPG), is a colorless, odorless, slightly viscous liquid with the formula C3H8O2 and a molecular weight of 76.09 g/mol. It belongs to the diol family, is completely miscible with water, and has a low melting point of about -59 °C, which is why it never freezes in normal cold storage. PG boils at 188.2 °C and has a closed-cup flash point of about 99 °C, making it far less flammable than ethanol or acetone. It is also very stable and does not easily volatilize, so it stays where it is put, which is exactly what food and cosmetic formulators need from a humectant.
Why Is Propylene Glycol Used in Food?
Propylene glycol performs several jobs in processed food: it absorbs and holds moisture (humectant), keeps flavors and colors evenly dispersed, prevents oil and water phases from separating, and acts as a carrier for flavoring extracts. That is why a cake mix stays moist, salad dressings do not split, and soft drinks, candy and bakery products keep a consistent texture on the shelf.
Foods that commonly contain propylene glycol include baked goods and desserts, baking and flavoring mixes, prepared meals, candy, soft drinks, some breads, dairy products, condiments, canned beans, popcorn, and most fast food. It is also used to keep dried herbs, spices and food colors flowing freely. In addition to food, PG is a standard ingredient in cosmetics, toothpaste, e-liquid carriers, pharmaceuticals and veterinary products.
How Safe Is Propylene Glycol?
The U.S. Food and Drug Administration (FDA) classifies propylene glycol as Generally Recognized as Safe (GRAS) for its intended uses in food, and it is listed as food additive E1520 in the European Union. The European Food Safety Authority (EFSA) has established an acceptable daily intake (ADI) of 25 mg per kilogram of body weight per day, and the Joint FAO/WHO Expert Committee on Food Additives (JECFA) has set a similar limit. Typical dietary exposure stays far below these levels.
Propylene glycol has a very low acute toxicity. In the body, about 45% of ingested PG is excreted unchanged by the kidneys, and the remainder is oxidized to lactate and pyruvate through normal metabolic pathways. The main documented adverse effects are limited to individuals with a specific sensitivity or to cases of gross over-consumption, which are rare. It is important not to confuse PG with ethylene glycol: ethylene glycol is toxic and is not approved for food use, whereas propylene glycol is safe at authorized levels.
Food-Grade Propylene Glycol Specifications
| Parameter | Value |
|---|---|
| CAS number | 57-55-6 |
| Molecular formula | C3H8O2 |
| Molecular weight | 76.09 g/mol |
| Boiling point | 188.2 °C |
| Melting point | -59 °C |
| Flash point (closed cup) | About 99 °C |
| Density at 20 °C | 1.036 g/cm³ |
| Appearance | Colorless, clear, viscous liquid |
| Solubility | Completely miscible with water and ethanol |
| Common grades | USP / EP (pharma), food grade, industrial grade |
Buying Food-Grade Propylene Glycol in Bulk
When purchasing PG for food, pharmaceutical or cosmetic use, specify the USP or EP grade and request the Certificate of Analysis (COA) confirming identity, purity and impurity profile, plus the SDS for handling. Bulk product is typically shipped in 230 kg drums, IBC totes of 1000 - 1200 kg, or ISO tanks for larger volumes. PG is not classified as a dangerous good for transport in most cases, which simplifies international shipping, but always confirm the applicable regulations for your route and packaging.
Frequently Asked Questions
Is propylene glycol safe to eat? Yes, at authorized levels. The FDA lists PG as GRAS for food use and EFSA allows 25 mg per kg of body weight per day, a level far above normal dietary intake.
Which foods contain propylene glycol? Baked goods and mixes, salad dressings, soft drinks, candy, dairy products, condiments, canned beans, popcorn and many prepared meals and fast-food items can contain PG as a humectant, solvent or carrier.
What is the difference between propylene glycol and ethylene glycol? Ethylene glycol is a toxic antifreeze chemical, while propylene glycol is a low-toxicity food-grade compound. Only propylene glycol (CAS 57-55-6) is approved for food, cosmetic and pharmaceutical use.
Is propylene glycol the same as monopropylene glycol? Yes. Monopropylene glycol (MPG) and propylene glycol are the same substance, 1,2-propanediol (CAS 57-55-6), and the terms are used interchangeably in trade.
Can propylene glycol cause allergic reactions? Some individuals with rare sensitivities may react to PG in cosmetics or foods, but such cases are uncommon. Everyone else metabolizes it safely at normal intake levels.
What documentation should I request when buying food-grade PG? Request the COA for each lot, the SDS, and a statement of compliance with USP/EP or food-grade specifications, plus any allergen or GMO declarations your market requires.