Dipropylene glycol (DPG) is a synthetic liquid widely used in cosmetics, fragrances, and industrial formulations, and the weight of toxicology evidence supports its safety at the concentrations people typically encounter. Regulatory reviews by cosmetic-ingredient panels have concluded it is safe as used in personal-care products, and long-term animal studies have found no cancer-causing potential. That said, the full picture involves nuances around dose, route of exposure, and individual sensitivity that are worth understanding if you use products containing this ingredient or work with it in an occupational setting.
What DPG Actually Is
Dipropylene glycol belongs to the propylene glycol family, a group of compounds produced by reacting propylene oxide with water. The resulting liquids are clear, viscous, colorless, have very little odor, and mix completely with water.1Kirk-Othmer Encyclopedia of Chemical Technology. Glycols, Propylene Glycols DPG is essentially two propylene glycol units joined together, which gives it a higher molecular weight and makes it slightly thicker and less volatile than its simpler cousin, monopropylene glycol (MPG). It exists as a mixture of three structural variations, or isomers, though for most practical purposes they behave similarly.
You will encounter DPG in an unexpectedly broad range of products. In the fragrance industry, it serves as a carrier and diluent for perfume oils, helping scents disperse evenly without overpowering the blend with its own smell. In skincare and cosmetics, it works as a humectant, meaning it pulls moisture from the environment into the skin’s surface layer, and as a solvent that helps other ingredients dissolve and spread uniformly. Beyond personal care, DPG appears in printing inks, hydraulic fluids, plasticizers, and even as a component in some aircraft de-icing formulations. Its ability to mix with both water and oily substances, combined with its low toxicity profile, makes it a go-to industrial solvent.
How DPG Behaves on Your Skin
One of the first safety questions people raise about any cosmetic ingredient is whether it penetrates the skin and, if so, how much enters the body. Researchers have measured this directly for DPG using human abdominal skin samples in the lab. Over a 24-hour period, roughly 9% of an applied dose of DPG penetrated through the skin, with a steady-state penetration rate of about 39 micrograms per square centimeter per hour.2PubMed. Dermal penetration of propylene glycols: measured absorption across human abdominal skin in vitro and comparison with a QSAR model That is a relatively modest absorption rate, and it is less than half the rate measured for monopropylene glycol under the same conditions. The larger molecular size of DPG slows its passage through the skin barrier.
Occupational health assessments have reinforced this picture. A detailed evaluation published in The MAK Collection concluded that DPG causes very slight irritation of skin and eyes, if any, and that skin contact does not contribute meaningfully to systemic toxicity. Based on that evidence, the panel withdrew a previous notation flagging DPG as a potential concern for skin absorption.3The MAK Collection for Occupational Health and Safety. Dipropylene glycol In plainer terms, the amount that gets through your skin during normal product use is too small to cause internal harm.
Eye exposure is a slightly different story. When tested on rabbit eyes, propylene glycols as a group produced mild to severe ocular irritation, though hexylene glycol was the worst offender in the group, not DPG.4Journal of the American College of Toxicology. Final Report on the Safety Assessment of Butylene Glycol, Hexylene Glycol, Ethoxydiglycol, and Dipropylene Glycol This matters mostly for people who might accidentally splash a concentrated solution in their eyes in a workplace setting. In a finished cosmetic product, DPG is diluted enough that eye irritation is unlikely, but it is still a good idea to rinse thoroughly if a product containing it gets into your eyes.
What Long-Term Animal Studies Revealed
The most comprehensive look at DPG’s internal safety comes from the National Toxicology Program (NTP), which ran drinking-water studies in rats and mice lasting up to two years. In shorter-term studies spanning two weeks to three months, animals were given DPG at concentrations up to 80,000 parts per million (ppm) in their water. At that extreme dose, male rats showed testicular atrophy and related reproductive-organ changes.5Toxicology. Toxicology and carcinogenesis studies of dipropylene glycol in rats and mice To put 80,000 ppm in perspective, that is 8% of the animals’ entire water supply replaced by DPG, a concentration wildly beyond anything a person would ever encounter through normal product use.
In the two-year studies, doses topped out at 40,000 ppm. At that level, male rats weighed less than controls, and all male rats in the 40,000 ppm group died before the study ended, primarily from kidney disease.6PubMed. NTP toxicology and carcinogenesis studies of dipropylene glycol in F344/N rats and B6C3F1 mice (drinking water studies) Female rats and all mice at lower doses survived at rates comparable to untreated controls. The kidney damage seen in male rats at extreme concentrations is a pattern specific to certain rat strains and does not necessarily predict what would happen in humans, though it signals that DPG is not harmless in unlimited quantities.
The finding that matters most for everyday safety is the cancer question. Across all dose groups and both species, the NTP found no increase in tumor rates.6PubMed. NTP toxicology and carcinogenesis studies of dipropylene glycol in F344/N rats and B6C3F1 mice (drinking water studies) The two-year study confirmed that treatment-related neoplastic lesions did not occur in rats or mice.5Toxicology. Toxicology and carcinogenesis studies of dipropylene glycol in rats and mice This is strong evidence, because two-year rodent bioassays are specifically designed to detect carcinogenic potential. DPG passed cleanly.
The Cosmetic Safety Verdict
The Cosmetic Ingredient Review (CIR) panel, which independently evaluates ingredients used in personal-care products, assessed DPG alongside several related glycols. After reviewing acute, subchronic, and chronic oral toxicity data across multiple animal species, as well as inhalation and skin-exposure studies, the panel concluded that the glycols collectively showed a low order of toxicity. The specific conclusion for DPG was that it is safe as presently used in cosmetics.4Journal of the American College of Toxicology. Final Report on the Safety Assessment of Butylene Glycol, Hexylene Glycol, Ethoxydiglycol, and Dipropylene Glycol DPG also appears on the U.S. Food and Drug Administration’s list of substances generally recognized as safe for use in food-contact applications and indirect food additives, and it is accepted by the European Chemicals Agency under REACH regulations for its range of industrial and consumer uses.
The “as presently used” qualifier is important. The CIR panel evaluates ingredients at the concentrations actually found in finished products on the market, not at the extreme doses used in animal toxicity studies. In practice, DPG typically appears at single-digit percentages in cosmetics and at higher concentrations in fragrance concentrates that are further diluted before reaching the consumer. At those levels, the toxicological margin of safety is wide.
Allergic Reactions and Individual Sensitivity
While DPG is well tolerated by the overwhelming majority of people, rare cases of allergic contact dermatitis have been documented. A case report described a patient who developed allergic contact dermatitis from DPG present in a hydrocortisone lotion, confirmed by patch testing.7Wiley Online Library. Allergic contact dermatitis from dipropylene glycol in hydrocortisone lotion This is worth knowing, because DPG is used as an excipient (an inactive carrier ingredient) in some topical medications. If you develop a rash from a medicated cream or lotion and the active ingredient is one you have used without trouble before, the solvent or carrier could be the culprit.
True allergy to DPG appears to be uncommon, though it is probably underdiagnosed simply because DPG is not included in most standard patch-test series that dermatologists use to screen for contact allergies. If you suspect a reaction, ask your dermatologist to test DPG specifically. People who are already sensitive to propylene glycol (MPG) may be at somewhat higher risk, since the two molecules share structural features, but cross-reactivity is not guaranteed. Many people who react to one tolerate the other without issues.
Environmental Profile
DPG released into the environment does not persist indefinitely. Both chemical breakdown and microbial digestion reduce its concentrations over time. Studies on propylene glycol ethers as a class found significant aerobic biodegradation across multiple test conditions, with half-lives in the range of 5 to 25 days in surface water, soil, and wastewater treatment systems.8PubMed. An examination of the physical properties, fate, ecotoxicity and potential environmental risks for a series of propylene glycol ethers DPG itself may be on the slower end of that range. A separate study that tested DPG’s biodegradability under raw sewage conditions found it began to degrade moderately only after more than three weeks of exposure to sewage microorganisms.9Environmental Toxicology. Biodegradability and microbial toxicity of aircraft fuel system icing inhibitors
Aquatic toxicity studies paint DPG as relatively benign for waterways at realistic concentrations. LC50 values for propylene glycol ethers ranged from roughly 100 to over 20,000 milligrams per liter for freshwater fish, invertebrates, and algae, meaning it takes very high concentrations to harm aquatic life.8PubMed. An examination of the physical properties, fate, ecotoxicity and potential environmental risks for a series of propylene glycol ethers At low concentrations, DPG did not significantly inhibit microbial activity.9Environmental Toxicology. Biodegradability and microbial toxicity of aircraft fuel system icing inhibitors The main environmental concern arises when large volumes are released at once, such as from airport de-icing operations, where runoff concentrations can temporarily spike high enough to deplete dissolved oxygen in nearby waterways as microbes consume the glycol. Under normal consumer-product use, the amounts reaching the environment are far too dilute to cause ecological harm.
How DPG Compares to Related Glycols
One source of confusion for consumers is the alphabet soup of glycols that appear on ingredient labels. Not all glycols are created equal, and some names that sound similar carry very different risk profiles.
Monopropylene glycol (MPG), the simpler single-unit version of DPG, is even more widely used. It shows up in food, pharmaceutical products, and e-cigarette liquids. MPG penetrates skin at roughly twice the rate of DPG, but it also has an excellent safety record at normal use levels and is approved as a direct food additive.2PubMed. Dermal penetration of propylene glycols: measured absorption across human abdominal skin in vitro and comparison with a QSAR model Both MPG and DPG are considered low-toxicity compounds.
Hexylene glycol, another member of the glycol family, was found to be more irritating to rabbit skin and eyes than DPG in the same CIR safety assessment.4Journal of the American College of Toxicology. Final Report on the Safety Assessment of Butylene Glycol, Hexylene Glycol, Ethoxydiglycol, and Dipropylene Glycol Hexylene glycol was still deemed safe for cosmetic use, but the comparison highlights that DPG sits at the gentler end of the spectrum within its chemical family.
The glycol to genuinely worry about is diethylene glycol (DEG), an entirely different compound that has caused mass poisoning events when it contaminated medicines. DEG is metabolized into toxic acids in the body and can cause fatal kidney failure. DPG and DEG are sometimes confused because their names overlap phonetically, but their toxicity profiles are worlds apart. DPG does not produce the dangerous metabolites that make DEG lethal. If you see “dipropylene glycol” on a label, you are looking at a low-toxicity ingredient, not the substance behind contamination scandals.
Reading Labels and Making Practical Decisions
On cosmetic and fragrance product labels, DPG typically appears under its full name or occasionally as its CAS registry number (25265-71-8). In the European Union, it shows up on ingredient lists in its INCI (International Nomenclature of Cosmetic Ingredients) name, which is simply “Dipropylene Glycol.” Its position on the ingredient list gives you a rough sense of concentration: ingredients are listed in descending order by weight, so DPG appearing near the top of a long list means a higher concentration than DPG appearing near the bottom.
For most people, there is no reason to avoid DPG in cosmetics, fragrances, or household products. The evidence from long-term animal studies, dermal absorption measurements, and decades of real-world use supports its safety at the concentrations found in consumer goods. The situations where caution is warranted are narrow: known sensitivity to propylene glycol-family ingredients, unexplained contact dermatitis from a product containing DPG, or occupational settings where workers handle concentrated DPG without gloves or eye protection for extended periods. In those cases, substitution or protective equipment is a reasonable precaution.
People sometimes see the word “glycol” and assume a connection to ethylene glycol, the toxic antifreeze component. The propylene glycol family is chemically and toxicologically distinct from ethylene glycol. This is one of the more persistent misconceptions in ingredient-label discussions, and it leads to unnecessary worry. Not every compound with “glycol” in its name poses the same risks, just as not every compound with “acid” in its name will burn you. DPG’s safety record is robust, and its continued inclusion in thousands of consumer products reflects a genuine consensus among toxicologists and regulators rather than industry oversight.