Propylene glycol first showed up in the early 20th century after chemists shifted from wood-based alcohols to petroleum-derived chemicals. Some early patents from the 1930s describe its synthesis from propylene oxide, and by the 1940s, it became a staple for the military and the food industry alike. Looking back, wartime drove demand for antifreeze and chemical intermediates, so major chemical plants scaled up production. As petrochemicals took over many markets, formulations changed and processes became safer, leading to today’s reliable industrial chemistry networks.
Propylene glycol often carries the E-number E1520 in food, turning up in pharmaceutical syrups, skin creams, and e-cigarettes as a humectant and solvent. Tanks of the stuff roll out from chemical producers to food factories, cosmetics labs, and even ice rinks, where the glycol circulates through freezing pipes. Despite its industrial roots, it's common around the house: deodorants, hair products, and pet foods count on its ability to mix oil and water, hold moisture, and deliver flavors. The biggest producers include branded names such as Dow and BASF, shipping thousands of tons to both high-tech and everyday buyers.
Visually, propylene glycol comes across as a nearly clear, slightly syrupy liquid. It tastes faintly sweet, carrying almost no odor, and it mixes with both water and alcohol without a fuss. This ability to blend so many substances extends its use well beyond food into paints, resins, and even smoke machines for theater performances. Its boiling point hovers around 187°C, but it starts vaporizing at much lower temperatures when used in fog machines or humidifiers. Its chemical formula, C3H8O2, gives two alcohol groups, making it a stable partner in many reactions and tough to break down in normal storage.
Manufacturers stamp barrels and drums with tight tolerances: above 99.5% purity for pharmaceutical or food applications, less for industrial grades. Standard labeling warns of safe handling, batch number, and regulatory compliance—whether from the FDA, USP, or European food authorities. Typical specs track water content, color, acidity, and specific gravity, aiming for consistency. Regulatory handbooks also stamp codes and hazard symbols: not flammable at room temperature, not classified as hazardous in low volumes, but still worth treating with respect. For anyone in food and pharma, the smallest contaminant raises red flags—so documentation runs deep and thorough.
Large tanks feed propylene oxide gas into reactors containing water or sometimes a small amount of acid to boost reaction speed. Chemists separate the result into two main products: denser 1,2-propylene glycol and lighter compounds such as dipropylene glycol. Distillation removes most impurities, and the liquid cools before moving to quality-control labs. Pressure and temperature settings depend on reactor design but typically stay high enough to keep the reaction moving fast and pure. Scale plays a part: small labs batch out a few liters for specialty uses while huge chemical plants produce thousands of tons through continuous processes.
At its core, propylene glycol reacts as a diol, so it bonds freely with acids, isocyanates, and some anhydrides to form plastics, resins, or even pharmaceuticals. Skincare chemists look for esterification reactions—linking glycol to fatty acids to make emollients for softening skin. In the lubricant industry, the alcohol groups link to fatty acids for synthetic coolants. Research teams often use the glycol backbone as a scaffold for new drugs or biocompatible plastics. The chemistry runs deep but tends to be robust; the two alcohol groups open up options for hundreds of derivatives without much fuss or hazardous byproducts.
On paperwork, it’s listed by names such as 1,2-propanediol, propane-1,2-diol, PG, and monpropylene glycol. Older chemical catalogs feature labels like methylethylene glycol or alpha-propylene glycol. Packaged goods sometimes list “E1520” as the only identifier. In technical sales, buyers often just ask for “PG” and specify “USP” or “industrial grade” to mark the difference between medicine-cabinet and machinery use. Translators and customs paperwork complicate things in international shipping, but the backbone structure—three carbons, two alcohols—remains unmistakable.
Safety training uses propylene glycol as a classic example for chemical handling: experts agree on mask, gloves, and eye protection around large volumes. Food- and pharma-grade glycol follows batch control rules set by global agencies, tracking every tank from source to final product. The chemical itself rarely irritates skin or eyes, but spills get sticky, and large vapor clouds can choke up unventilated spaces, especially in poorly run workshops. Fire marshals check with the National Fire Protection Association labeling, which tags it as “minor fire hazard.” Regulatory bodies such as OSHA and NIOSH provide exposure limits. Anyone making foods or medicines follows the FDA’s rules for residue, labeling, and traceability.
The diversity of uses for propylene glycol comes from its basic scientific strengths: it carries flavor, helps medicine dissolve, keeps things moist, and prevents freezing. Food technicians use it in everything from cake batters to food colorings. Vape juice manufacturers depend on it to carry nicotine and flavors in e-cigarettes. Medical injection drugs use it as a vehicle for steroids and vitamins, allowing fine-tuned dosing. Even breweries and dairies rely on glycol chilling systems to keep tanks at precise temperatures during fermentation. Car repair shops—those old enough to remember “toxic antifreeze”—now use propylene glycol blends for engine cooling. Sporting arenas freeze ice with glycol-based coolants, giving skaters and hockey players smooth fast surfaces.
Research branches out in two key directions: new uses and cleaner manufacturing. Teams at universities investigate improved catalysts for synthesis to lower emissions and save on energy. Polymer scientists experiment with new copolymers and biocompatible materials, using glycol as a central building block. In health science, teams evaluate propylene glycol’s effect on drug absorption and skin barrier function. Environmental engineering researchers monitor its breakdown in wastewater and soil to address the risk of glycols leaking from broken coolant pipelines. As consumer habits change—think plant-based meats, vaping, and green chemistry—manufacturers seek cheaper, renewable sources, driving investigation of bio-based propylene glycol from corn or glycerin.
Veterinary cases involving cats and dogs shaped much of what experts know about propylene glycol toxicity—cats, in particular, show red blood cell changes at higher doses, leading food safety authorities to recommend against its use in cat foods. In humans, the U.S. FDA recognizes it as Generally Recognized as Safe (GRAS) in foods, so accidental ingestion doesn't trigger panic, but some people do react with minor skin redness or digestive upset. Toxicologists have tracked metabolic breakdown: humans convert it to lactic acid, then CO2, with little accumulation. Large accidental overdoses, mostly in hospital settings involving intravenous use, do draw concern and get flagged in medical literature. For the public, the biggest cause for alarm lies in misinformation—online rumors often blur the line between safe levels and industrial misuse. Still, ongoing research tracks long-term effects and cumulative exposure, focusing on vulnerable groups like infants and patients on certain medications.
Demand for safer, greener chemicals guides propylene glycol’s future. Biorefineries now turn corn and sugar beets into renewable glycols, and big chemical players scale up investments in low-carbon production. Electric vehicles and new cooling technologies in data centers open up new need for non-toxic, non-freezing fluids, so suppliers invest in reformulating blends that last longer and protect expensive equipment. Cosmetics and food companies seek “vegan-certified” labels, tightening requirements on where the glycol comes from. Regulators periodically review scientific evidence, keeping manufacturers on their toes and forcing ongoing improvement in purity and traceability. Opportunities keep growing in medical delivery systems, flavor science, and advanced manufacturing, riding a wave of data from citizen science, corporate research, and stricter global oversight.
Propylene glycol seems to hide in plain sight. Glance over the back of a food label, and it might turn up. Walk down the aisles of a hardware store, and it shows up in antifreeze. A lot of folks never think about it, even though it quietly shapes the way products work in kitchens and garages alike.
I started reading food labels a few years ago, trying to avoid artificial colors for my kids. Propylene glycol popped up in a tub of frosting. Most people don’t realize how often processed foods contain it. Propylene glycol plays a role in keeping food moist and helping flavors blend. Ice cream is smoother with it, and salad dressing stays mixed instead of separating. The amount in foods falls well below the safety limits set by the FDA, but some people worry about long-term effects. Food isn’t the only place that stirs up concern. The European Union takes a different approach and chooses stricter limits, which highlights how safety opinions don’t always line up worldwide.
Hardware stores sell solutions called “RV antifreeze” or “non-toxic antifreeze” that keep plumbing safe in cold weather. Unlike other chemicals, propylene glycol won’t cause health scares if a little leaks into drinking water lines—something that matters for boats, vacation cabins, or kids’ backyard playhouses. I’ve used it for my family’s camper every winter. Pour it down the pipes before storing the camper away, and I know it’s safe come spring.
In the bathroom, propylene glycol appears on ingredient lists for lotions, shampoos, and deodorants. Besides keeping things from drying out, it helps dissolve ingredients so they spread more evenly. For people with sensitive skin, sometimes this creates problems—skin reactions can happen, especially if you already struggle with eczema. Doctors use a medical version that’s very pure. The medication for my son’s fever contained it as a stabilizer, helping the active ingredient dissolve and stay usable longer. Propylene glycol’s safety, especially in medicines and baby products, draws ongoing study. Researchers keep a close eye on cumulative exposure, which matters for those using many products each day.
Some people worry about hidden risks. Stories spread fast online, and it’s tough for families to sort fact from fear. Here’s how I learned to cope: check sources, stick with brands that share manufacturing details, and talk with health professionals when in doubt. One step toward easing these concerns comes from pushing for full disclosure on labels. Consumers need to know what’s in their food and personal care products, especially for those with allergies or medical conditions.
Better research and clearer regulations can protect those who feel vulnerable. More studies looking at lifetime exposure, especially for children or the elderly, guide future decision-making. Since propylene glycol appears in so many parts of daily life, giving shoppers real access to facts builds trust. I’ve learned it’s not about avoiding every chemical—it’s about knowing which ingredients matter to your family and making choices that feel right for you.
Look into your pantry or that energy drink on the shelf. You’ll spot “propylene glycol” on more ingredient lists than you might guess, from processed foods to salad dressings and even in some medications. Propylene glycol isn’t some exotic chemical. It’s a colorless, nearly tasteless liquid, and food makers use it as a stabilizer, a carrier for flavors, and a way to keep things moist or blended.
Scientists and doctors have watched propylene glycol closely over the years. The Food and Drug Administration has labeled food-grade propylene glycol as “generally recognized as safe” for use in food products, so long as it stays below set limits.
The World Health Organization also gave it a go-ahead for human consumption at levels up to 25 milligrams per kilogram of body weight per day. For an average adult, that translates into several grams a day—far more than you’d find in your average diet.
Researchers look at cases where people ingest it in realistic amounts, and the truth is, for most of us, our bodies process and get rid of it efficiently. Usually, the body converts it into lactic acid. This process doesn’t stack up inside healthy folks.
Anything added to your food deserves scrutiny. For the vast majority, low intake seems to cause few troubles. Some people react differently, though. For example, those with a rare enzyme deficiency called “propionic acidemia” can struggle to clear propylene glycol. Infants under six months have less ability to break it down, so their intake gets special attention, especially in hospital settings.
Instances of mild irritation or allergic reactions do pop up. Take skin care: it sometimes causes rashes or itching. Not common due to food, but worth mentioning if you get an upset stomach or other reactions after certain packaged treats.
Folks worry because propylene glycol resembles ethylene glycol, a toxic chemical found in antifreeze, but these compounds behave differently in the body. Drinking a bottle of antifreeze is life-threatening. Consuming small amounts of food-grade propylene glycol doesn’t carry those hazards.
Rumors put doubt in people’s minds about anything with an unfamiliar name, especially if it sounds technical. The idea that propylene glycol sits in antifreeze or exists in e-cigarette liquids adds fuel to these fears. Context gets lost fast online, but food-grade propylene glycol isn’t the same stuff pumped into radiators.
When my family discusses “chemical” ingredients, I always point out how dose and context matter just as much as the name on the label. A sprinkle in cake mix barely compares to a jug in a machine, and our bodies evolved to handle all sorts of organic compounds.
Some bakeries and small food makers prefer to skip synthetic additives altogether, leaning on more “natural” thickeners or humectants. Glycerin does similar work in foods and cosmetics, but it isn’t always a one-for-one swap. Natural doesn’t always mean safer; it depends on the person and the amount.
If you prefer fewer additives, read the labels and seek out brands using simpler formulas. The more informed you are, the easier it becomes to make choices that match your own comfort level.
More research wouldn’t hurt, especially given how diets and ingredient exposures keep changing. Listening to your body, keeping up with trustworthy science, and avoiding fear-based headlines go a long way in sorting out fact from confusion. Food safety isn’t static, and staying aware keeps people in charge of what ends up in their meals.
Propylene glycol shows up just about everywhere. It slides into ingredient lists for foods, skin creams, medications, and e-cigarettes. The FDA tags it as “generally recognized as safe,” and most people chew and slather without a second thought. I once worked at a bakery where we used cake icing tubs laced with propylene glycol. The thought never occurred to me that it might cause any trouble—until a coworker with sensitive skin broke out in a rash after cleaning up. That sent me down a rabbit hole of research, and here’s what I found out.
People bump into propylene glycol most often through their food or personal care routine. For most, it goes unnoticed. Some individuals run into allergy-like reactions. They might see hives, itchy skin, or irritation, especially if the product sits on their skin for a long time. I’ve seen folks with eczema or sensitive skin get red, angry patches where lotions or soaps stuck around too long.
The American Contact Dermatitis Society named propylene glycol “Allergen of the Year” a few years back. That kind of nod doesn’t come out of nowhere. Even low-strength solutions can irritate skin that struggles with other chemicals. Small kids and people with chronic skin conditions face greater risk. Doctors have documented cases of allergic contact dermatitis, sometimes from something as simple as a topical cream or baby wipe.
Less often, people carry sensitivities straight to the lungs. Propylene glycol sits at the heart of most e-cigarette liquids. Early research points to coughing, dry throat, and airway irritation among new e-cigarette users. In 2022, a study done by the CDC showed that propylene glycol vapor could dry out airway tissues, sometimes leading to wheezing or chest tightness.
After entering the body, propylene glycol breaks down into lactic acid and pyruvic acid, then flushes out through the kidneys. Most adults handle this just fine. Hospitals sometimes use it to dilute drugs given by injection. Trouble crops up with high doses or repeated exposure. The folks most at risk include people with kidney or liver problems, young children, and elderly patients. Reports have included seizures, irregular heartbeat, and kidney issues with medical-grade exposures. One journal article from the New England Journal of Medicine tracked cases where people developed acidosis—when the blood turns acidic—after large amounts reached their system.
Medical journals document cases of high propylene glycol buildup in patients receiving heavy doses of intravenous drugs. That is rare for everyday folks, but knowing about the risk matters for anyone living with chronic health conditions.
The big takeaway: Reading labels stays important. If someone has sensitive skin, eczema, asthma, or a kidney issue, double-checking ingredients and asking an allergist makes sense. The solution isn’t frantic avoidance—most people can use products containing this chemical safely. Companies have options to cut back on propylene glycol or replace it with less irritating alternatives, especially as more people share stories of allergy or irritation.
It helps that new research keeps turning up about lesser-known sensitivities. That points to the value of listening to your own body, checking with healthcare professionals, and not brushing off weird reactions as “no big deal.” After all, if a change in soap or snack means better health, the switch won’t hurt.
The names sound confusingly similar, but propylene glycol and ethylene glycol can't be used interchangeably. Both show up in antifreeze, yet one could save your life and the other could threaten it. People end up making mistakes with these chemicals—sometimes with tragic consequences.
Propylene glycol comes from petroleum or plant sources. It’s a clear, tasteless liquid with the chemical formula C3H8O2. Most folks run into it in food, skin creams, and even inhalers. In the food world, it acts as a stabilizer. Regulators like the US Food and Drug Administration and European Food Safety Authority have both said it’s safe in small amounts.
Ethylene glycol looks similar on paper—C2H6O2—but packs more of a toxic punch. It’s colorless, kind of syrupy, and sweet to the taste, which might tempt pets or kids. It gets used because it can lower freezing points, making it a go-to for car antifreeze or de-icing runway fluid. Swallowing it by accident holds real danger; cases of poisoning usually need medical intervention.
Every winter, you’ll see stories pop up about animals or children getting sick after sipping up spilled antifreeze. I’ve heard from local veterinarians who see cats and dogs rushed in, often too late for help—ethylene glycol can destroy kidneys fast. Newer antifreeze options use propylene glycol as a safer option since it carries far less risk if ingested.
You don’t want ethylene glycol lurking in food or medicine. Even a small amount can trigger nausea, followed by kidney failure. I’ve learned to double-check labels; the difference between a food safe and a deadly toxin boils down to a few letters.
There’s a myth that “glycol” means something is poisonous. That’s not true. Propylene glycol sees heavy use in all sorts of everyday products. The World Health Organization gave it a seal of approval for food use at reasonable levels. Worry crops up because the word “glycol” sticks in people’s minds—news stories often skip the difference, stoking unneeded panic.
Antifreeze producers color ethylene glycol bright green or yellow to make accidental swaps less likely. Still, mistakes happen. Tighter rules on clear product labeling have helped, but some older brands still look too similar. Stores keep antifreeze bottles high on shelves, away from the reach of curious small hands. Doctors and poison control centers stress the importance of prompt action if exposure ever happens.
Propylene glycol’s safety comes from toxicology studies that look at how our bodies handle it. The body can break it down and flush it out with few problems for most people. Still, folks with kidney or liver trouble—or sensitive pets—should take extra care in environments where either glycol shows up.
You only get one shot at safety with household chemicals. Propylene glycol pops up in foods, medicines, and fluffy soft ice cream. Ethylene glycol belongs under the hood, away from the kitchen or medicine cabinet. Reading labels—especially on products that could be ingested—makes the biggest difference. If something seems off, don’t guess; double-check before use. Safer choices and informed habits can stop accidents before they start.
Walk into any pharmacy or grocery store, and odds are, you'll find propylene glycol in everything from skin creams to cake mixes. Even asthma inhalers use it. The FDA has called it “generally recognized as safe,” and food scientists use it as a stabilizer and moisture-retaining agent. It’s in personal care products and even the vaping liquids that have surged in popularity. Sometimes, folks don’t realize how common it has become in daily routines.
I remember standing in line at the corner pharmacy, overhearing a mother tell the pharmacist her son broke out in an itchy, red rash after using a cream for eczema. The pharmacist started asking questions, ran his finger down the label, and mentioned propylene glycol. That conversation stuck with me because I’d never really thought about what’s in moisturizers or how common ingredients can impact sensitive skin.
Not everyone reacts to propylene glycol, but some do. Reactions might show up as a red, itchy rash—especially where the product touched the skin. Sometimes there’s stinging, swelling, or burning. Doctors call this “allergic contact dermatitis,” and it pops up in folks whose immune systems get triggered by this substance.
Dermatologists keep seeing these cases. A study published in “Contact Dermatitis” reported about 1% to 3.8% of people tested had allergic reactions to it. Many don't trace the rash back to a lotion, toothpaste, or sanitizer. That’s a challenge, since allergic contact dermatitis can look like eczema, drug reactions, or other types of skin irritation.
Most people use products with propylene glycol and never flinch. Probably 99 times out of 100, nothing happens. Companies keep using it because it works: creams become smoother, food stays fresh, and medications stay stable. The allergic reactions, while real for some, don’t outweigh the benefits for the wider population who use these goods safely each day.
People with known sensitivities—or unexplained skin problems—should watch ingredients. The solution starts with better labeling and transparency from manufacturers. Big brands have begun offering “sensitive skin” options without propylene glycol, but shoppers may need to look hard for them on busy shelves.
Dermatology clinics now carry testing kits for contact allergies, which provide answers for people stumped by mysterious rashes. I’ve talked to patients who got relief just by switching toothpaste or hand sanitizer. When skin is already sensitive, basic steps matter: patch testing before slathering on a new product, focusing on simple ingredient lists, and working with healthcare professionals who listen closely.
Propylene glycol doesn’t cause problems for everyone, but for the few who react, the results can be frustrating. Companies and consumers can work together—through labeling, smarter choices, and more attention from healthcare providers—to make sure that avoiding these reactions doesn’t require a chemistry degree.
| Names | |
| Preferred IUPAC name | propane-1,2-diol |
| Other names |
1,2-Propanediol Propane-1,2-diol PG Methylethylene glycol Trimethyl glycol |
| Pronunciation | /ˈproʊpəliːn ˈɡlaɪkɒl/ |
| Identifiers | |
| CAS Number | 57-55-6 |
| Beilstein Reference | 1718734 |
| ChEBI | CHEBI:16997 |
| ChEMBL | CHEMBL1276 |
| ChemSpider | 6350 |
| DrugBank | DB00876 |
| ECHA InfoCard | ECHA InfoCard: 01-2119456809-23-XXXX |
| EC Number | 200-338-0 |
| Gmelin Reference | Gm: 2174 |
| KEGG | C01407 |
| MeSH | D011382 |
| PubChem CID | 1030 |
| RTECS number | UA0350000 |
| UNII | 6DC9Q167V3 |
| UN number | UN3076 |
| Properties | |
| Chemical formula | C3H8O2 |
| Molar mass | 76.09 g/mol |
| Appearance | Colorless, odorless, viscous liquid |
| Odor | Odorless |
| Density | 1.036 g/cm³ |
| Solubility in water | Miscible |
| log P | -0.92 |
| Vapor pressure | 0.129 hPa (20 °C) |
| Acidity (pKa) | 14.6 |
| Basicity (pKb) | 15.10 |
| Magnetic susceptibility (χ) | -12.4 × 10⁻⁶ cm³/mol |
| Refractive index (nD) | 1.431 |
| Viscosity | 40-60 mPa·s (at 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) | -545.5 kJ/mol |
| Std enthalpy of combustion (ΔcH⦵298) | -2004 kJ/mol |
| Pharmacology | |
| ATC code | A16AX10 |
| Hazards | |
| Main hazards | May cause eye irritation, skin irritation, and respiratory tract irritation. |
| GHS labelling | Non-hazardous according to GHS |
| Pictograms | GHS07,GHS08 |
| Signal word | Warning |
| Hazard statements | No hazard statement. |
| NFPA 704 (fire diamond) | 1-1-0 |
| Flash point | 103°C |
| Autoignition temperature | 371°C |
| Lethal dose or concentration | LD50 Oral Rat 20,000 mg/kg |
| LD50 (median dose) | 20,000 mg/kg (rat, oral) |
| NIOSH | RN8400000 |
| PEL (Permissible) | 50 ppm |
| REL (Recommended) | 50 mg/m³ |
| Related compounds | |
| Related compounds |
Ethylene glycol 1,3-Propanediol Glycerol Dipropylene glycol |
