Propanediol is not toxic at the concentrations found in skincare, food, or personal care products. The version you’ll encounter most often, 1,3-propanediol, has an oral lethal dose in rodents between 10,500 and 15,789 mg per kilogram of body weight. For context, that places it in the lowest toxicity category, comparable to table salt. The U.S. FDA reviewed it and raised no questions about its safety for food use, and the Cosmetic Ingredient Review expert panel concluded it is safe in cosmetics at current use concentrations.
Which Propanediol Are We Talking About?
Two chemicals share the propanediol name, and the distinction matters. 1,3-propanediol (the one listed on most skincare and food labels) has its two chemical groups spaced apart on a three-carbon chain. 1,2-propanediol, better known as propylene glycol, has those groups right next to each other. Both are made of three carbon atoms and two hydroxyl groups, and their safety profiles are similar, but they’re not identical.
The version showing up in newer cosmetics and personal care products is almost always 1,3-propanediol. It’s typically produced through fermentation of corn sugar by engineered bacteria, a process developed commercially by DuPont Tate & Lyle. This bio-based origin is why you’ll sometimes see it marketed as “plant-derived” or “natural” on ingredient lists. Propylene glycol, by comparison, has traditionally been derived from petroleum, though both are considered safe for their intended uses.
Toxicity at a Glance
The EPA reviewed the acute toxicity data for 1,3-propanediol and found it remarkably low-risk. The oral LD50 (the dose that would be lethal to half of test animals) ranges from 10,500 to 15,789 mg/kg of body weight. To put that in practical terms, a 150-pound person would need to consume an almost impossibly large quantity in one sitting for it to be dangerous. For inhalation, the lethal concentration in rats exceeded 5.0 mg per liter of air, which again places it well outside any realistic exposure scenario.
An inhalation study testing 1,3-propanediol at 1,800 mg per cubic meter of air found that it does not appear to pose a significant hazard through breathing in either gas or aerosol form. This is particularly relevant for people who encounter it in spray products, humectant mists, or electronic cigarette liquids.
How It Compares to Propylene Glycol
If you’ve researched propylene glycol before, you may have seen warnings about skin and airway irritation. Major propylene glycol manufacturers have declined to support its use in electronic cigarettes or theatrical fog machines because of potential effects on eye, nose, throat, and respiratory tissue. In the cosmetics world, 1,3-propanediol is recognized and used specifically as a non-irritant alternative.
The thermal behavior difference is worth noting too. When heated, propylene glycol and glycerol can break down into toxic volatile compounds including formaldehyde, acetaldehyde, and acrolein. Research published in Scientific Reports found that 1,3-propanediol produces fewer thermal decomposition byproducts than either propylene glycol or glycerol. At normal vaporization temperatures, it evaporates without any thermal decomposition at all. This makes it a safer option in any application involving heat.
Regulatory Status
1,3-propanediol holds a strong safety record across multiple regulatory bodies. The FDA accepted a GRAS (Generally Recognized As Safe) notice for it in 2010, permitting its use as a food ingredient at levels up to 24% in confections and frostings, 5% in alcoholic beverages, 2.5% in frozen dairy products, and 2% in most other food categories. The only exclusions are infant formula, fish, meat, and poultry.
For cosmetics, the Cosmetic Ingredient Review expert panel assessed propanediol alongside nine other related compounds in 2023. Of the ten ingredients reviewed, seven were deemed safe in cosmetics at present practices of use and concentration. Propanediol was among the seven that passed. The three flagged as having insufficient data were different chemicals entirely: 1,4-butanediol, 2,3-butanediol, and octanediol.
Skin Irritation and Allergic Reactions
Most of the contact dermatitis literature focuses on propylene glycol (1,2-propanediol) rather than 1,3-propanediol, which reflects how rarely the latter causes problems. Propylene glycol is a known cause of both irritant and allergic contact dermatitis, though it tends to be a weak sensitizer. Patch testing studies found that no irritation occurred in a group of 204 people tested with 12% propylene glycol, while slight irritation appeared in some subjects at 30% and above.
One notable finding: in a study of 38 patients who had positive skin patch reactions to propylene glycol, 15 developed a rash within 3 to 16 hours of swallowing it. None of the 20 control patients reacted. This suggests that people with a known propylene glycol sensitivity can react through ingestion, not just skin contact. If you’ve had confirmed reactions to propylene glycol, it’s reasonable to be cautious with 1,3-propanediol as well, since the two compounds are structurally very similar.
For the vast majority of people, though, 1,3-propanediol causes no irritation. Its use in cosmetics is partly motivated by being gentler than propylene glycol, and it actually doubles as a mild preservative. Research found that 1,3-propanediol is more effective than propylene glycol at killing common bacteria like E. coli and Pseudomonas, working by damaging their cell membranes. This antimicrobial activity means it can help keep your products stable without additional harsh preservatives.
Where You’ll Encounter It
Propanediol serves primarily as a humectant, meaning it helps products retain moisture and improves the texture of creams, serums, and lotions. You’ll find it in moisturizers, cleansers, hair conditioners, foundations, and deodorants. In food, it works as a solvent for flavorings and a texture modifier in baked goods and confections. It also appears in some pharmaceutical formulations as a carrier ingredient.
At the concentrations used in these products (typically well under 10% in skincare, and within the FDA’s specified limits in food), 1,3-propanediol presents no meaningful toxicity risk. It is one of the better-studied cosmetic ingredients, with safety data covering oral, dermal, and inhalation routes, and it consistently lands in the lowest concern categories across all of them.