Propylene glycol entered the industrial world during the early 20th century, right as chemical engineering opened up new practical materials for every type of manufacturer. Theodore L. Hull patented a method to manufacture propylene glycol from propylene oxide in the 1920s. Dow Chemical and Union Carbide soon took the lead in its bulk production, using propylene obtained from cracking petroleum fractions. Before this, glycerol filled most roles that propylene glycol fills today, but shortages during World War II drove researchers to alternatives. Laboratories and production lines gradually adopted it thanks to its non-toxicity and water-solubility, so it appeared in everything from antifreeze to food processing before most people had indoor plumbing.
Propylene glycol stands out as a colorless, nearly odorless, and tasteless liquid, showing up in pharmacy bottles, food factories, and even fog machines. You can find it on the ingredient list of processed foods, in skin-care serums, as a solvent in oral and topical medicines, and in sectors like tobacco and animal feed. Its characteristic trait stems from how well it attracts and holds water, which lets it blend with a huge variety of substances. As a result, it straddles pharmaceutical, food, cosmetic, and industrial domains with rare versatility.
Unlike ethylene glycol, which comes with real risks, propylene glycol earns its reputation for safety. It has the molecular formula C3H8O2 and a molecular weight of approximately 76.09 g/mol. Its boiling point hovers around 188°C, and it remains liquid down to -59°C, making it practical for cold-weather antifreeze. The miscibility with water, acetone, and chloroform drives its widespread use. With a high flash point—over 100°C—propylene glycol avoids the flammability problem of other solvents. These traits reshape how companies formulate consumer and technical products.
On any propylene glycol drum, clear numbers mark the standard: USP (United States Pharmacopeia), FCC (Food Chemicals Codex), or industrial grade. USP and FCC grades guarantee purity that meets both food and drug safety standards, hitting minimum assays of 99.5% purity or higher. Industrial uses permit minor contamination with water or other glycols, but bulk food and pharmaceutical handlers choose the cleanest product to avoid liability and batch recalls. Labeling usually highlights the CAS registry number 57-55-6 so handlers can ensure they're using the right compound; it's become a mainstay identifier across regulatory documentation worldwide.
Most plants make propylene glycol by hydrating propylene oxide, a process using either direct, non-catalytic hydration or a catalyst-assisted indirect route. In direct hydration, mixing propylene oxide and water at elevated temperature and pressure delivers high yields, and recycling steps grab remaining starting materials. The indirect pathway uses a strong acid catalyst, creating intermediate glycols that get separated through distillation. Chemical engineers prefer direct methods for efficiency—they squeeze more glycol out of every ton of propylene oxide. Steam and careful pressure control finish the job, and purification steps strip out residual water and co-products so the final liquid flows clear.
Propylene glycol participates in a suite of chemical reactions. Its two hydroxyl groups react easily—one primary, one secondary—allowing it to combine into polymers or esters with a range of functional properties. Chemical industries rely on propylene glycol as a building block for making unsaturated polyester resins, which go into paints, fiberglass, and boat-building materials. It also survives mild oxidation, breaking down to lactic and pyruvic acids, which are biodegradable and environmentally friendlier than many alternatives. Chemical engineers leverage these reactions when seeking sustainable manufacturing routes or when synthesizing specialty solvents and plasticizers.
Most chemical handbooks list propylene glycol under synonyms like 1,2-propanediol or propane-1,2-diol. The industry uses abbreviations like PG, MPG (for monopropylene glycol), and at times methylethylene glycol. Commodity names sometimes appear under trade labels from chemical suppliers—DowFrost, Propasol, and DOW PG are just a few. Scientific and technical communication sticks to "propylene glycol" for clear identification, but regulatory sheets must acknowledge its various names to help handlers avoid confusion, especially where similar-sounding glycols carry different hazards.
Consumer trust and regulatory approval both hinge on the safety profile and reliable management of propylene glycol. Large-scale producers follow strict occupational guidelines published by OSHA, ACGIH, and the European Chemicals Agency. Inhalation and dermal exposure limits exist, though propylene glycol rarely causes toxicity under normal use—it’s recognized as “Generally Recognized As Safe” (GRAS) by the FDA for food and pharmaceutical use. Storage regulations focus on spill prevention, as slippery films create hazards in industrial areas and run-off could strain local water treatment plants. Use in e-cigarettes has provoked new reviews, with research underway to probe long-term inhalation effects. Factories now act with extra caution, embracing best-practices for exhaust filters and personal protective equipment, out of both legal obligation and ethical standards.
Propylene glycol blends into daily life far beyond factory gates. Food processors use it as a carrier for flavors, emulsifiers, and stabilizers. Skin-care companies value it for its gentle moisturizing properties and role as a non-irritating solvent. Pharmaceutical labs turn to PG as a vehicle for injectable and oral solutions, especially for drugs requiring water-miscible carriers. It’s the base for theatrical fog, de-icers, and non-toxic antifreeze, protecting both public venues and plumbing infrastructure. Pet foods and feeds benefit from its low toxicity; livestock ingest it safely as an energy source. This sheer scope pushes suppliers to maintain production volumes in the hundreds of thousands of tons annually, attesting to its trusted role on factory lines and in household goods.
Laboratories around the world keep finding new roles for propylene glycol as regulatory agencies tighten standards on solvent safety. Researchers explore bio-based feedstocks, aiming to shift the molecular origins of propylene oxide away from petroleum, using fermentative or catalytic routes based on glycerin or lactic acid. Polymer chemists continue to fine-tune copolymers and resins that use propylene glycol as a central component, testing biodegradability, compatibility, and new mechanical properties for advanced materials. Environmental toxicologists also dig deeper, testing environmental breakdown pathways and metabolic fates in aquatic systems, especially with new scrutiny on the widespread use of chemicals in e-liquids and vapor products. Funding now follows projects that combine green chemistry with product safety, reflecting growing global concerns.
The low acute toxicity profile of propylene glycol has secured its place in medicines and foods, but emerging research asks tougher questions about chronic and vulnerable population exposure. Animal studies set high thresholds for adverse effects, yet clinical reports have documented rare cases of toxicity in patients with kidney or liver impairment; neonates and critically ill individuals face different metabolic risks. Medical literature now tracks cases of lactic acidosis and central nervous system depression, particularly after intravenous infusions involving large doses over sustained periods. European and American health authorities review and update usage limits for food and topical products periodically, following surveillance of allergic reactions and rare hypersensitivity cases. The growing use in electronic cigarettes has sparked aerosol toxicity studies. Researchers measure pulmonary and cardiovascular effects, though major outcomes remain subject to debate and ongoing research.
As environmental policy shifts and consumer awareness climbs, propylene glycol’s future looks tied to renewable feedstocks and even cleaner safety records. Plants soon may rely more on fermentation-derived glycols or on integrated biorefineries converting agricultural waste streams into propylene oxide. Green chemistry initiatives press manufacturers to cut process energy and emissions, pushing both innovation and regulatory change. Meanwhile, synthetic chemistry keeps opening new frontiers in biodegradable plastics, smart coatings, and safer antifreeze blends. This chemical’s broad versatility will likely keep it on the approved lists across regulatory agencies, but continuous transparency, better chronic toxicity data, and robust lifecycle assessments will set the pace for responsible development.
Propylene Glycol, often showing up on ingredient lists as PG, seems to turn up just about everywhere. I’ve seen it in cake mixes, heard about it in conversations around vaping, and noticed it in skin creams stacked at the pharmacy. This clear, syrupy liquid comes from petroleum, bringing both convenience and questions, especially for anyone interested in what goes into everyday products.
Anyone who’s ever compared an old muffin to a fresh one knows texture counts. PG helps keep baked goods from drying out. In ice cream, it stops crunchy ice crystals from crashing the party, giving each bite a steady, creamy feel. It’s classified by the FDA as “generally recognized as safe” for use in small amounts. According to the World Health Organization, even at standard exposure levels across food and consumer products, this compound almost never triggers dangerous effects.
Take a look at cough syrup, allergy medicines, or even certain prescription injectables. PG pops up again. It acts as a solvent, letting medicines dissolve completely so each spoonful or pill gives a reliable dose. In lotions and creams, PG draws water from the air toward your skin. Folks with dry patches, eczema, or sensitive skin often find comfort from products containing this ingredient. Rarely, some people notice irritation, and doctors always suggest patch testing for those with a record of reactions.
From the shampoo in my shower to the toothpaste in my drawer, PG manages to sneak a spot. It helps keep liquids flowing just right, not too thick or too runny. Even in antifreeze, PG steps in, replacing the more toxic ethylene glycol. Pets and kids wandering into the garage face much less danger compared to past decades, though swallowing any chemical should always lead to a call to poison control.
PG’s popularity shot up with the rise of e-cigarettes. Its role in producing vapor feels impossible to ignore. Though it allows for flavors to mix and clouds to form, inhalation safety remains the subject of studies. Current research, including reviews in medical journals, finds inhaling limited amounts doesn’t threaten health for most. Asthmatics and those with lung issues sometimes struggle, however, and news stories have highlighted allergic responses from time to time. Long-term effects still need closer inspection, given vaping’s relative newness.
Some people feel uneasy spotting chemical names on their product labels. Experience tells me learning more about why these ingredients show up goes a long way. Fact-checking, asking doctors, and following trusted health sources helps cut through the noise. Countries review research on PG every year, tweaking regulations if new risks surface. For now, normal use in food, cosmetics, or medicine doesn’t spark a red flag from major health agencies. Still, concerned shoppers can search out “PG-free” versions—brands are listening and creating options. That’s a consumer win.
What makes the difference in product safety isn’t always the chemical itself but how much ends up in the mix. Manufacturers must list PG by name, and tighter labeling standards have pushed companies to share more details. Apps and online resources put ingredient research in everyone’s pocket. Regular government checks keep dishonest brands off the shelves.
Safe innovation depends on straight talk about ingredients. As research and consumer pressure evolve, companies will find new ways to build trust and offer healthy choices beyond just swapping one additive for another.
Propylene glycol stands out in ingredient lists for everything from salad dressings to cough syrups to vape liquids. People sometimes confuse it with ethylene glycol, which is toxic, but they're different chemicals. Propylene glycol is a synthetic liquid, and the FDA has labeled it "generally recognized as safe" (GRAS) in food and pharmaceuticals. Its versatile, moisture-retaining quality makes it appealing for keeping products from drying out.
I’ve found this ingredient in ice cream, cake frosting, and even prepackaged shredded cheese. It works as a stabilizer and helps keep the texture smooth. On a personal level, I didn’t notice its presence until I began reading the backs of food labels more closely. It surprised me to see it pop up in so many household staples, even though its amounts tend to be low.
Regulatory agencies in the U.S., Canada, and Europe have studied propylene glycol and placed limits on how much can be present in food or medicine. The FDA set a maximum content in prepared foods—50 grams for every kilogram of product. The European Food Safety Authority reviewed its use as a food additive in 2018 and agreed with established limits, concluding that most people stay well below the thresholds.
Scientists have looked at the way the body deals with propylene glycol. After swallowing it, most people break it down in the liver and get rid of it in urine. At low levels in foods or medicines, it rarely causes side effects. Research points out that high levels—from misuse or large accidental exposures—could stress the kidneys or nervous system, especially in very young children or in adults with certain liver conditions. The most widely reported reactions are mild or allergic, and they’re more common with products sitting on the skin than those eaten.
Every once in a while, a viral article or post warns about propylene glycol, often making the link to antifreeze (ethylene glycol). That’s misleading. Toxic antifreeze and the stuff in food sit on very different chemical branches. Propylene glycol’s widespread use, the rigorous studies, and global regulatory opinions all point away from alarmism.
Still, people's concerns about food safety matter. Those who eat a lot of processed foods could see regular exposure add up. Just as eating lots of salt or added sugar raises questions about diet over time, so does the regular intake of helpful but synthetic compounds. People with eczema or allergies may want to watch their intake, since sensitivity can show up as skin irritation or tummy discomfort.
Many shoppers express a growing preference for short ingredient lists. If a product contains something unfamiliar, that can spark worry. I try to shop for food with ingredients I recognize, when possible. Cooking at home helps me skip unintuitive chemicals and gives me control over what goes on my plate. Less exposure usually means lower risk.
Not everyone wants or can avoid shelf-stable foods. So, a balanced approach may work best. Reading ingredient labels helps consumers understand what they’re eating. If propylene glycol appears, it might help to check how high it sits on the list—a higher spot usually signals a bigger dose. If allergies or special health needs exist, consult with a healthcare provider, especially for children. If you want to avoid it, many brands now offer versions without synthetic stabilizers. We always have a real say in what comes home from the store.
Propylene glycol (PG) and vegetable glycerin (VG) both appear on ingredient labels in products most folks use daily. You spot PG in foods, cosmetics, and even inhalers for asthma, while VG pops up in sweeteners, lotions, and cough syrups. The main difference runs deeper than just their source. PG starts from petroleum or natural gas, giving it a synthetic profile, while VG comes from plant oils like coconut or soy. Those origins matter, especially to people looking for plant-based or non-petroleum options, either for health reasons or environmental concerns.
One big reason these two pop up so much in the world of vaping has to do with their texture and behavior. PG feels thinner, almost watery, which lets it absorb flavors easily. This makes it popular among folks who want a stronger, cleaner taste from e-liquids. VG, with its syrupy texture, brings a certain smoothness and helps create those thick, billowy vape clouds that some users aim for. From talking with vapers, I’ve seen how a mix of both often helps balance flavor intensity and vapor production.
Both PG and VG have a track record of being added to foods and medicines for decades. The FDA generally recognizes PG as safe in small amounts, but some people report throat irritation or dry mouth. VG, drawn from plant sources, usually causes fewer reactions, although it can feel sticky or leave a lingering sweetness. I’ve noticed extra sensitivity to PG in my family, especially for anyone with allergies or asthma, which aligns with studies showing PG can worsen respiratory symptoms in rare cases.
The roots of these chemicals change the game for anyone thinking about sustainability or animal-free choices. Propylene glycol relies mostly on oil industries. Vegetable glycerin, with its plant base, appeals to vegans and those who want less reliance on fossil fuels. Still, folks should remember that big-scale farming for VG can bring up problems like pesticide use or deforestation, especially when sourced from unsustainable palm or soy crops. My own attempts at buying truly sustainable VG taught me the label “vegetable” doesn’t guarantee an ethical footprint.
It’s easy to take things at face value, especially in a world loaded with claims like “natural” or “safe.” Not all PG and VG on the market gets processed to food or pharma grade. Inconsistent quality means impurities can sneak in, and that brings risks, including toxicity from tainted batches. Over the years, I’ve seen companies switch suppliers, sometimes quietly, which raises transparency issues. Regulators in places like the United States and European Union set tough purity rules, but consumers still do best by checking brands and looking for reputable certifications.
Choosing between PG and VG often comes down to your needs and values—taste, allergies, ethical sourcing, or environmental impact. For anyone mixing or buying products with these two, paying attention to labels and going with trusted suppliers gives peace of mind. Discussion about PG and VG reminds me that simple ingredients can carry big conversations about safety, sustainability, and personal preference.
Just about everyone comes across propylene glycol. It shows up in everything from ice cream to cough syrup, and you’ll even spot it listed on makeup, lotion, and vape juice labels. The stuff helps keep things moist, blends ingredients, and helps carry flavors. To most people, it sounds pretty harmless, a standard part of the long ingredient lists in modern products. Still, anyone who cares about what they put on and in their body ought to ask questions—especially about side effects or allergic reactions.
Propylene glycol rarely puts folks in the hospital, but some people do run into trouble. In my own circle, a friend noticed his skin started itching and burning after switching to a new deodorant. A dermatologist pointed to propylene glycol as the skin irritant. This wasn’t just a one-off. The American Contact Dermatitis Society actually flagged it as an allergen years ago. In some people, mostly those with sensitive skin or existing eczema, it can cause rashes or worsen irritation. Kids seem to react more, especially when it’s in wipes or lotions applied to inflamed areas.
Ingesting small amounts doesn’t faze most adults. The FDA has marked it as safe for food use in limited amounts. That’s good to know—most folks down a lot more of it than they realize because it hides in coffee creamers, sodas, and all those “moist” cakes at the grocery store. On the other hand, if someone takes high doses (think large-volume medicine or when used intravenously in hospitals over a long stretch), propylene glycol can build up in the system and cause problems. There are documented cases where it affected the kidneys or even led to confusion, slowed heart rate, or breathing issues, especially if someone already has kidney issues.
People who use e-cigarettes or vape pens come across it, too. Heating and inhaling propylene glycol has led to sore throats, headaches, or shortness of breath in some users. The science keeps shifting as habits and studies grow, but if you find yourself sensitive to many additives, chances are the vapor isn’t doing you any favors.
Most toxicology studies say the danger for most people is low, especially at the amounts in food or cosmetics. Health authorities in the United States and Europe have all looked at the evidence and drawn similar conclusions. The outlier groups—those with allergies, kidney issues, small kids, the elderly—deserve extra caution. These effects aren’t just theoretical, and ignoring the possibility can make matters worse down the line. The National Library of Medicine notes that allergic skin reactions keep showing up in medical literature. It’s not hype; it’s history recorded by dermatologists everywhere.
One reason propylene glycol pops up so often? It works. It makes creams smooth, helps syrups blend, stabilizes flavors, and extends shelf life. But people deserve a chance to figure out if it’s right for them. Read ingredient labels. If you deal with allergies, ask the doctor about testing or alternatives—especially for kids or anyone with sensitive skin. In hospitals, health teams are moving toward safer substitutes for patients who need large amounts of medicines or IV fluids. It’s also smart to keep track of reactions. A rash or persistent cough could reveal an intolerance you never expected. The onus falls on both manufacturers and consumers: companies need to keep researching, and people need to stay aware, report symptoms, and push for safer choices.
Propylene glycol makes modern products work better. Its side effects don’t show up everywhere, but for susceptible folks, even a common additive can spark frustration or pain. By knowing the risks, asking questions, and seeking alternatives when needed, everyone gets a chance to make smarter, safer choices about the products that fill their homes and lives.
Propylene glycol shows up everywhere—skin creams, processed foods, e-liquids, even in some forms of antifreeze. It’s clear, it’s got pretty good shelf life, and, for the most part, people don’t notice it as they use daily products. All this talk about sustainability and what we’re dumping into landfills, rivers, and the air naturally drags these hidden chemicals into the spotlight. Plenty of household and industrial chemicals don’t have a friendly legacy. So, how does propylene glycol stack up?
Propylene glycol biodegrades quite well, especially compared to relatives like ethylene glycol. In soil and water, bacteria can munch away at propylene glycol, breaking it down into simpler compounds fairly quickly. Research from the U.S. EPA and other groups suggests this process generally takes between a few days up to a week, depending on conditions. This makes a difference at wastewater plants, where chemicals with slow or incomplete breakdown can stick around and cause trouble. Since propylene glycol doesn’t linger or accumulate, threats to aquatic life remain much lower than feared. Fish and other water creatures suffer less when exposed, with toxicity levels ranking lower than many other solvents and additives.
The story complicates at the start. The most common way to make propylene glycol involves petroleum. Most products still pull from fossil fuels, raising the specter of climate change and resource depletion. Some companies have switched to bio-based production, using corn or other crops instead. Every renewable option brings its own problems: using farmland for chemical feedstocks eats into space that could grow food, and big monocultures rely on fertilizer and water, which both have their impacts.
So finding a global solution means looking at the entire life cycle—from planting all the way through disposal. Any improvement here relies on balancing resource use, pollution, and social needs. Biodegradability checks one box, but unless we solve where the raw material comes from, we only patch up parts of the problem.
Accidental spills, like those seen with airplane de-icing fluids, land in rivers and creeks every winter. Even biodegradable chemicals can cause real-world trouble if they show up in big enough quantities. High concentrations can lower oxygen levels in the water while they break down, which stresses or kills fish. City stormwater systems and airports pay a lot more attention now; better containment and recovery efforts chip away at large-scale damage, but they don’t erase it entirely.
Businesses serious about shrinking their environmental impact look for greener sources and smarter waste handling. Choosing bio-based propylene glycol makes sense in some cases, as long as growth and processing don’t turn the process into another strain on the land. Handling runoff responsibly, treating contaminated water, and re-thinking bulk uses like de-icing all matter just as much.
For consumers, picking products with fewer unnecessary chemicals and supporting brands that shift to better sourcing can nudge the market. Still, the real improvement grows from broad cooperation between science, regulators, manufacturers, and buyers who don’t see “biodegradable” as a magic word but as one part of a bigger, ongoing conversation about what really counts as environmentally responsible.
| Names | |
| Preferred IUPAC name | propane-1,2-diol |
| Other names |
1,2-Propanediol
Propane-1,2-diol Methylethylene glycol 1,2-Dihydroxypropane Dowfrost PG |
| Pronunciation | /ˈprɒpɪliːn ˈɡlaɪkɒl/ |
| Identifiers | |
| CAS Number | 57-55-6 |
| Beilstein Reference | 969591 |
| ChEBI | CHEBI:16997 |
| ChEMBL | CHEMBL115197 |
| ChemSpider | 7470 |
| DrugBank | DB00876 |
| ECHA InfoCard | 100.045.276 |
| EC Number | 200-338-0 |
| Gmelin Reference | 58852 |
| KEGG | C00476 |
| MeSH | D011382 |
| PubChem CID | 1030 |
| RTECS number | TY2000000 |
| UNII | 6DC9Q167V3 |
| UN number | UN3077 |
| Properties | |
| Chemical formula | C3H8O2 |
| Molar mass | 76.09 g/mol |
| Appearance | Colorless, odorless, and tasteless viscous liquid |
| Odor | Odorless |
| Density | 1.036 g/cm³ |
| Solubility in water | Completely soluble |
| log P | -0.92 |
| Vapor pressure | 0.13 hPa (20°C) |
| Acidity (pKa) | 14.8 |
| Basicity (pKb) | 15.1 |
| Magnetic susceptibility (χ) | '-9.90 × 10⁻⁶ cm³/mol' |
| Refractive index (nD) | 1.431 - 1.433 |
| Viscosity | 42.0 mPa·s (20°C) |
| Dipole moment | 2.33 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 198.0 J·mol⁻¹·K⁻¹ |
| Std enthalpy of formation (ΔfH⦵298) | −510.0 kJ/mol |
| Std enthalpy of combustion (ΔcH⦵298) | -2020 kJ/mol |
| Pharmacology | |
| ATC code | A16AX10 |
| Hazards | |
| Main hazards | Harmful if swallowed. Causes serious eye irritation. May cause respiratory irritation. |
| GHS labelling | GHS07, GHS08 |
| Pictograms | GHS07 |
| Signal word | Not Classified |
| Hazard statements | Not a hazardous substance or mixture. |
| Precautionary statements | P210, P233, P240, P241, P242, P243, P280, P370+P378 |
| NFPA 704 (fire diamond) | 1-1-0 |
| Flash point | 103°C (217°F) |
| Autoignition temperature | 371°C (700°F) |
| Explosive limits | 2.6% - 12.5% |
| Lethal dose or concentration | LD50 (oral, rat): 20,000 mg/kg |
| LD50 (median dose) | 20,000 mg/kg (rat, oral) |
| NIOSH | RN8400 |
| PEL (Permissible) | 50 ppm |
| REL (Recommended) | 8 mg/m³ |
| IDLH (Immediate danger) | No IDLH established. |
| Related compounds | |
| Related compounds |
Ethylene Glycol (EG)
Dipropylene Glycol (DPG) Tripropylene Glycol (TPG) Propylene Oxide Glycerol Butylene Glycol |
