PROPYLENE GLYCOL

Synonyms:
1,2-propanediol; propylene glycol; MPG; propane-1,2-diol; 57-55-6; 1,2-Propylene glycol; 1,2-dihydroxypropane; 2-Hydroxypropanol; Methylethyl glycol; Methylethylene glycol; Isopropylene glycol; Monopropylene glycol; Dowfrost; Sirlene; Trimethyl glycol; 2,3-Propanediol; Propylene Glycol USP; Solargard P; alpha-Propyleneglycol; Solar Winter; BAN; dl-Propylene glycol; DL-1,2-Propanediol; Ucar 35; SentryPropylene Glycol; 1,2-Propylenglykol; (RS)-1,2-Propanediol; (+-)-1,2-Propanediol; Propylène Glycol 12; (+-) Propylene glycol; FEMA No. 2940; propylenglycol; alpha-Propylene glycol; Caswell No. 713; (+/-)-1,2-propanediol; 1,2-Propylenglykol [German]; Prolugen; .alpha.-Propylene glycol; 1,2-(RS)-Propanediol; Ilexan P; 1,2-propandiol; 1,2-propane-diol; Propan-1,2-Diol; L-1,2-propanediol; EINECS 200-338-0; S-(+)-Propylene glycol; General lube; 1,2-Propanediol, 99%, extra pure; Propylene Glycol (Propane-1,2-diol); 1,2-Propanediol, 99+%, for analysis; CAS-57-55-6; 1,2 Propanediol; S(+)-Propylene glycol; All purpose lubricant; Polypropylene glycol 1,000; Propylene glycol [USP:JAN]; Propylene glycol [USAN:JAN]; propylene-glycol; Aliphatic alcohol; Centella Asiatica; Chilisa FE; 1.2-propanediol; a-Propylene glycol; 1,2 -propanediol; 1,2-propyleneglycol; Propylene glycol, USP; Average MW 1000; Propylene glycol (TN); racemic propylene glycol; ACMC-1AMKJ; Propylene glycol dl-form; racemic 1,2-propanediol; prop-2-ene-1,2-diol; propilen glycol; PROPILEN GLIKOL; Propilen Glikole;  Propilen Glicole

PROPYLENE GLYCOL

Propylene glycol[1]
Propylene glycol
ball-and-stick model
Space-filling model
Names
Preferred IUPAC name
Propane-1,2-diol
Other names
Propylene glycol
α-Propylene glycol
1,2-Propanediol
1,2-Dihydroxypropane
Methyl ethyl glycol
Methylethylene glycol
Identifiers
CAS Number    
57-55-6 racemic check
4254-15-3 S-enantiomer
3D model (JSmol)    
Interactive image
ChEBI    
CHEBI:16997 check
ChEMBL    
ChEMBL286398 check
ChemSpider    
13835224 check
ECHA InfoCard    100.000.307 Edit this at Wikidata
EC Number    
200-338-0
E number    E1520 (additional chemicals)
PubChem CID    
1030
RTECS number    
TY6300000
UNII    
6DC9Q167V3 check
CompTox Dashboard (EPA)    
DTXSID0021206 Edit this at Wikidata
InChI[show]
SMILES[show]
Properties
Chemical formula    C3H8O2
Molar mass    76.095 g·mol−1
Appearance    colourless liquid
Odor    odorless
Density    1.036 g/cm3
Melting point    −59 °C (−74 °F; 214 K)
Boiling point    188.2 °C (370.8 °F; 461.3 K)
Solubility in water    Miscible
Solubility in ethanol    Miscible
Solubility in diethyl ether    Miscible
Solubility in acetone    Miscible
Solubility in chloroform    Miscible
log P    -1.34[2]
Thermal conductivity    0.34 W/m-K (50% H2O @ 90 °C (194 °F))
Viscosity    0.042 Pa·s

Propylene glycol
Propylene glycol (IUPAC name: propane-1,2-diol) is a viscous, colorless liquid, which is nearly odorless but possesses a faintly sweet taste. Its chemical formula is CH3CH(OH)CH2OH. Containing two alcohol groups, it is classed as a diol. It is miscible with a broad range of solvents, including water, acetone, and chloroform. In general, glycols are non-irritating and have very low volatility.[4]

It is produced on a large scale primarily for the production of polymers. In the European Union, it has E-number E1520 for food applications. For cosmetics and pharmacology, the number is E490. Propylene glycol is also present in propylene glycol alginate, which is known as E405. Propylene glycol is a compound which is GRAS (generally recognized as safe) by the US FDA (Food and Drug Administration) under 21 CFR x184.1666, and is also approved by the FDA for certain uses as an indirect food additive. Propylene glycol is approved and used as a vehicle for topical, oral, and some intravenous pharmaceutical preparations in the U.S. and in Europe.

Structure
The compound is sometimes called (alpha) α-propylene glycol to distinguish it from the isomer propane-1,3-diol, known as (beta) β-propylene glycol. Propylene glycol is chiral. Commercial processes typically use the racemate. The S-isomer is produced by biotechnological routes.

Production
Industrial
Industrially, propylene glycol is mainly produced from propylene oxide (for food-grade use). According to a 2018 source, 2.16 M tonnes are produced annually.[4] Manufacturers use either non-catalytic high-temperature process at 200 °C (392 °F) to 220 °C (428 °F), or a catalytic method, which proceeds at 150 °C (302 °F) to 180 °C (356 °F) in the presence of ion exchange resin or a small amount of sulfuric acid or alkali.[5]

1,2-Propandiol Synthesis V1.svg
Final products contain 20% propylene glycol, 1.5% of dipropylene glycol, and small amounts of other polypropylene glycols.[6] Further purification produces finished industrial grade or USP/JP/EP/BP grade propylene glycol that is typically 99.5% or greater. Use of USP (US Pharmacopoeia) propylene glycol can reduce the risk of Abbreviated New Drug Application (ANDA) rejection.[7]

Propylene glycol can also be obtained from glycerol, a byproduct from the production of biodiesel.[4] This starting material is usually reserved for industrial use because of the noticeable odor and taste that accompanies the final product.

Laboratory
S-Propanediol is synthesized from via fermentation methods. Lactic acid and lactaldehyde are common intermediates. Dihydroxyacetone phosphate, one of the two products of breakdown (glycolysis) of fructose 1,6-bisphosphate, is a precursor to methylglyoxal. This conversion is the basis of a potential biotechnological route to the commodity chemical 1,2-propanediol. Three-carbon deoxysugars are also precursor to the 1,2-diol.[4]

A small-scale, nonbiological route from D-mannitol is illustrated in the following scheme:[8]

(s)-Propanediol from D-Mannitol.png
Applications
Polymers
Forty-five percent of propylene glycol produced is used as a chemical feedstock for the production of unsaturated polyester resins. In this regard, propylene glycol reacts with a mixture of unsaturated maleic anhydride and isophthalic acid to give a copolymer. This partially unsaturated polymer undergoes further crosslinking to yield thermoset plastics. Related to this application, propylene glycol reacts with propylene oxide to give oligomers and polymers that are used to produce polyurethanes.[4] Propylene glycol is used in waterbased acrylic architectural paints to extend dry time which it accomplishes by preventing the surface from drying due to its slower evaporation rate compared to water.

Food
Propylene glycol is also used in various edible items such as coffee-based drinks, liquid sweeteners, ice cream, whipped dairy products and soda.[9][10] Vaporizers used for delivery of pharmaceuticals or personal-care products often include propylene glycol among the ingredients.[4] In alcohol-based hand sanitizers, it is used as a humectant to prevent the skin from drying.[11] Propylene glycol is used as a solvent in many pharmaceuticals, including oral, injectable, and topical formulations. Many pharmaceutical drugs which are insoluble in water utilize Propylène Glycol as a solvent and carrier; benzodiazepine tablets are one example.[12] PG is also used as a solvent and carrier for many pharmaceutical capsule preparations. Additionally, certain formulations of artificial tears use proplyene glycol as an ingredient.[13]

Propylene glycol is commonly used to de-ice aircraft
Antifreeze
The freezing point of water is depressed when mixed with propylene glycol. It is used as aircraft de-icing fluid.[4][14] Water-propylene glycol mixtures dyed pink to indicate the mixture is relatively nontoxic are sold under the name of RV or marine antifreeze. Propylene glycol is frequently used as a substitute for ethylene glycol in low toxicity, environmentally friendly automotive antifreeze. It is also used to winterize the plumbing systems in vacant structures.[15] The eutectic composition/temperature is 60:40 propylene glycol:water/-60 °C.[16][17] The −50 °F/−45 °C commercial product is, however, water rich; a typical formulation is 40:60.[18]

Electronic cigarettes liquid

Propylene glycol is often used in electronic cigarettes.
Along with vegetable glycerin as the main ingredient (<1–92%) in e-liquid used in electronic cigarettes, where it is aerosolized to resemble smoke. It serves as both the carrier for substances like nicotine and cannabinoids, as well as for creating a vapor which resembles smoke.[19]

Miscellaneous applications

A bottle of flavored e-liquid for vaping shows propylene glycol as one of the main ingredients along with vegetable glycerin.
Propylene glycol (often abbreviated 'PG') has many applications. Some common applications see PG used:

As a solvent for many substances, both natural and synthetic.[20]
As a humectant (E1520).
As a freezing point depressant for slurry ice.
In veterinary medicine as an oral treatment for hyperketonaemia in ruminants.[21]
In the cosmetics industry, where PG is very commonly used as a carrier or base for various types of makeup.[22]
For trapping and preserving insects (including as a DNA preservative).[23]
For the creation of theatrical smoke and fog in special effects for film and live entertainment. So-called 'smoke machines' or 'hazers' vaporize a mixture of PG and water to create the illusion of smoke. While many of these machines use a PG-based fuel, some use oil. Those which use PG do so in a process that is identical to how electronic cigarettes work; utilizing a heating element to produce a dense vapor. The vapor produced by these machines has the aesthetic look and appeal of smoke, but without exposing performers and stage crew to the harms and odors associated with actual smoke.[24][25]
As an additive in PCR to reduce the melting temperature of nucleic acids for targeting of GC rich sequences.
Safety in humans
When used in average quantities, propylene glycol has no measurable effect on development and/or reproduction on animals and probably does not adversely affect human development or reproduction.[26] The safety of electronic cigarettes—which utilize PG-based preparations of nicotine or THC and other cannabinoids—is the subject of much controversy.[27][28][29]

Oral administration
The acute oral toxicity of propylene glycol is very low, and large quantities are required to cause perceptible health effects in humans; in fact, propylene glycol is three times less toxic than ethanol.[30] Propylene glycol is metabolized in the human body into pyruvic acid (a normal part of the glucose-metabolism process, readily converted to energy), acetic acid (handled by ethanol-metabolism), lactic acid (a normal acid generally abundant during digestion),[31] and propionaldehyde (a potentially hazardous substance).[32][33][34] According to the Dow Chemical Company, The LD50 (Lethal Dose that kills in 50% of tests) for rats is 20 g/kg (rat/oral).[35][36]

Toxicity generally occurs at plasma concentrations over 4 g/L, which requires extremely high intake over a relatively short period of time, or when used as a vehicle for drugs or vitamins given intravenously or orally in large bolus doses.[37] It would be nearly impossible to reach toxic levels by consuming foods or supplements, which contain at most 1 g/kg of PG, except for alcoholic beverages in the US which are allowed 5 percent = 50g/kg.[38] Cases of propylene glycol poisoning are usually related to either inappropriate intravenous administration or accidental ingestion of large quantities by children.[39]

The potential for long-term oral toxicity is also low. In an NTP continuous breeding study, no effects on fertility were observed in male or female mice that received propylene glycol in drinking water at doses up to 10,100 mg/kg bw/day. No effects on fertility were seen in either the first or second generation of treated mice.[26] In a 2-year study, 12 rats were provided with feed containing as much as 5% propylene glycol, and showed no apparent ill effects.[40] Because of its low chronic oral toxicity, propylene glycol was classified by the U. S. Food and Drug Administration as "generally recognized as safe" (GRAS) for use as a direct food additive, including frozen foods such as ice cream and frozen desserts.[38][41] The GRAS designation is specific to its use in food, and does not apply to other uses.[42]

Skin, eye and inhalation contact
Propylene glycol is essentially non-irritating to the skin.[43] Undiluted propylene glycol is minimally irritating to the eye, producing slight transient conjunctivitis; the eye recovers after the exposure is removed. A 2018 human volunteer study found that 10 male and female subjects undergoing 4 hours exposures to concentrations of up to 442 mg/m3 and 30 minutes exposures to concentrations of up to 871 mg/m3 in combination with moderate exercise did not show pulmonary function deficits, or signs of ocular irritation, with only slight symptoms of respiratory irritation reported.[44] Inhalation of propylene glycol vapors appears to present no significant hazard in ordinary applications.[45] Due to the lack of chronic inhalation data, it is recommended that propylene glycol not be used in inhalation applications such as theatrical productions, or antifreeze solutions for emergency eye wash stations.[46] Recently, propylene glycol (commonly alongside glycerol) has been included as a carrier for nicotine and other additives in e-cigarette liquids, the use of which presents a novel form of exposure. The potential hazards of chronic inhalation of propylene glycol or the latter substance as a whole are as-yet unknown.[47]

According to a 2010 study, the concentrations of PGEs (counted as the sum of propylene glycol and glycol ethers) in indoor air, particularly bedroom air, has been linked to increased risk of developing numerous respiratory and immune disorders in children, including asthma, hay fever, eczema, and allergies, with increased risk ranging from 50% to 180%. This concentration has been linked to use of water-based paints and water-based system cleansers. However, the study authors write that glycol ethers and not propylene glycol are the likely culprit.[48][49][50]

Propylene glycol has not caused sensitization or carcinogenicity in laboratory animal studies, nor has it demonstrated genotoxic potential.[51][52]

Intravenous administration
Studies with intravenously administered propylene glycol have resulted in LD50 values in rats and rabbits of 7 mL/kg BW.[53] Ruddick (1972) also summarized intramuscular LD50 data for rat as 13-20 mL/kg BW, and 6 mL/kg BW for the rabbit. Adverse effects to intravenous administration of drugs that use propylene glycol as an excipient have been seen in a number of people, particularly with large bolus dosages. Responses may include CNS depression, "hypotension, bradycardia, QRS and T abnormalities on the ECG, arrhythmia, cardiac arrhythmias, seizures, agitation, serum hyperosmolality, lactic acidosis, and haemolysis".[54] A high percentage (12% to 42%) of directly-injected propylene glycol is eliminated or secreted in urine unaltered depending on dosage, with the remainder appearing in its glucuronide-form. The speed of renal filtration decreases as dosage increases,[55] which may be due to propylene glycol's mild anesthetic / CNS-depressant -properties as an alcohol.[56] In one case, intravenous administration of propylene glycol-suspended nitroglycerin to an elderly man may have induced coma and acidosis.[57] However, no confirmed lethality from propylene glycol was reported.

Animals
Propylene glycol is an approved food additive for dog and sugar glider food under the category of animal feed and is generally recognized as safe for dogs,[58] with an LD50 of 9 mL/kg. The LD50 is higher for most laboratory animals (20 mL/kg).[59] However, it is prohibited for use in food for cats due to links to Heinz body formation and a reduced lifespan of red blood cells.[60] Heinz body formation from Propilen Glikol has not been observed in dogs, cattle, or humans.

Allergic reaction
Estimates on the prevalence of propylene glycol allergy range from 0.8% (10% propylene glycol in aqueous solution) to 3.5% (30% propylene glycol in aqueous solution).[61][62][63] The North American Contact Dermatitis Group (NACDG) data from 1996 to 2006 showed that the most common site for propylene glycol contact dermatitis was the face (25.9%), followed by a generalized or scattered pattern (23.7%).[61] Investigators believe that the incidence of allergic contact dermatitis to propylene glycol may be greater than 2% in patients with eczema or fungal infections, which are very common in countries with lesser sun exposure and lower-than-normal vitamin D balances. Therefore, propylene glycol allergy is more common in those countries.[64]

Because of its potential for allergic reactions and frequent use across a variety of topical and systemic products, propylene glycol was named the American Contact Dermatitis Society's Allergen of the Year for 2018.[65][66] Recent publication from The Mayo Clinic reported 0.85% incidence of positive patch tests to propylene glycol (100/11,738 patients) with an overall irritant rate of 0.35% (41/11,738 patients) during a 20-year period of 1997–2016.[67] 87% of the reactions were classified as weak and 9% as strong. The positive reaction rates were 0%, 0.26%, and 1.86% for 5%, 10%, and 20% propylene glycol respectively, increasing with each concentration increase. The irritant reaction rates were 0.95%, 0.24%, and 0.5% for 5%, 10%, and 20% propylene glycol, respectively. Propylene glycol skin sensitization occurred in patients sensitive to a number of other concomitant positive allergens, most common of which were: Myroxylon pereirae resin, benzalkonium chloride, carba mix, potassium dichromate, neomycin sulfate; for positive propylene glycol reactions, the overall median of 5 and mean of 5.6 concomitant positive allergens was reported.

Environmental
Propylene glycol occurs naturally, probably as the result of anaerobic catabolism of sugars in the human gut. It is degraded by vitamin B12-dependent enzymes, which convert it to propionaldehyde.[68]

Propylene glycol is expected to degrade rapidly in water from biological processes, but is not expected to be significantly influenced by hydrolysis, oxidation, volatilization, bioconcentration, or adsorption to sediment.[69] Propylene glycol is readily biodegradable under aerobic conditions in freshwater, in seawater and in soil. Therefore, propylene glycol is considered as not persistent in the environment.

Propylene glycol exhibits a low degree of toxicity toward aquatic organisms. Several guideline studies available for freshwater fish with the lowest observed effect concentration of 96-h LC50 value of 40,613 mg/l in a study with Oncorhynchus mykiss. Similarly, the effect concentration determined in marine fish is a 96-h LC50 of >10,000 mg/l in Scophthalmus maximus.

Propylene Glycol in Food: Is This Additive Safe?
Propylene glycol is a substance commonly used as a food additive or ingredient in many cosmetic and hygiene products.

The US and European food authorities have declared it as generally safe for use in foods.

However, it has become controversial since it is also an ingredient in antifreeze. This had led to health concerns about possible toxic effects from eating foods that contain it.

This article investigates what propylene glycol is, why it is used and whether it is dangerous to your health.

What Is Propylene Glycol?
Propylene glycol is a synthetic food additive that belongs to the same chemical group as alcohol.

It is a colorless, odorless, slightly syrupy liquid that is a bit thicker than water. It has practically no taste (1Trusted Source).

Additionally, it can dissolve some substances better than water and is also good at retaining moisture. This makes it very useful as a food additive, so it can be found in a wide variety of processed foods and drinks (2).

Other names it is known by include (2):

1,2-propanediol
1,2-dihydroxypropane
Methyl ethyl glycol
Trimethyl glycol
Propylene glycol is sometimes confused with ethylene glycol, as both have been used in antifreeze due to their low melting points. However, these are not the same substance.

Ethylene glycol is highly toxic to humans and is not used in food products.

SUMMARY
Propylene glycol is a synthetic, colorless, odorless, tasteless liquid that belongs to the same chemical class as alcohol. It should not be confused with the toxic substance ethylene glycol.
Where and How Is It Used?
Propylene glycol is commonly used as an additive to aid in the processing of foods and improve their texture, flavor, appearance and shelf life.

In foods, propylene glycol may be used in the following ways (3, 4, 5):

Anti-caking agent: It helps prevent food components from sticking to one another and forming clumps, such as in dried soups or grated cheese.
Antioxidant: It extends the shelf life of foods by protecting them against deterioration caused by oxygen.
Carrier: It dissolves other food additives or nutrients to be used in processing, such as colors, flavors or antioxidants.
Dough strengthener: It modifies the starches and gluten in dough to make it more stable.
Emulsifier: It prevents food ingredients from separating, such as oil and vinegar in salad dressing.
Moisture preserver: It helps foods maintain a stable level of moisture and stops them from drying out. Examples include marshmallows, coconut flakes and nuts.
Processing aid: It is used to enhance the appeal or the use of a food, for example, to make a liquid clearer.
Stabilizer and thickener: It can be used to hold food components together or thicken them during and after processing.
Texturizer: It can change the appearance or mouthfeel of a food.
Propylene glycol is commonly found in many packaged foods, such as drink mixes, dressings, dried soups, cake mix, soft drinks, popcorn, food coloring, fast foods, bread and dairy products (6Trusted Source).

It is also used in injectable medications, like lorazepam, and in some creams and ointments that are applied to the skin, such as corticosteroids (2, 7Trusted Source).

Due to its chemical properties, it is also found in a wide variety of hygiene and cosmetic products. Additionally, it is used in industrial products like paint, antifreeze, artificial smoke and e-cigarettes (2, 6Trusted Source).

SUMMARY
Propylene glycol is commonly used as a food additive. It helps preserve moisture as well as dissolve colors and flavors. It is also used in some medications, cosmetic products, antifreeze and other industrial products.

Is Propylene Glycol in Food Dangerous?
Propylene glycol is “generally recognized as safe” (GRAS) by the US Food and Drug Administration (FDA) (8).

In the US, it can be used as a direct and indirect food additive. In Europe, it is only allowed to be used in food as a solvent for colors, emulsifiers, antioxidants and enzymes, with up to 0.45 grams per pound (1 gram/kg) allowed in the final food product (9Trusted Source).

The World Health Organization recommends a maximum intake of 11.4 mg of propylene glycol per pound of body weight (25 mg/kg) per day. The estimated exposure to propylene glycol through foods in the US is 15 mg per pound (34 mg/kg) per day (9Trusted Source).

In comparison, one person who developed symptoms of toxicity was receiving 213 grams of propylene glycol per day. For a 120-pound (60-kg) adult, that is over 100 times what is found in the average diet (9Trusted Source).

There is only one documented case of toxicity caused by food.

A man drank very large amounts of cinnamon whiskey containing propylene glycol and was found unconscious. While his symptoms were also due to the alcohol, some could be attributed to the propylene glycol (10Trusted Source).

Overall, apart from people with allergies and one case of excessive consumption, there have been no other reported cases of negative or toxic effects of propylene glycol in foods.

However, as current intakes are estimated to be above the recommended level, it may be wise to reduce dietary sources where you can, especially as the primary sources are highly processed foods.

SUMMARY
Propylene glycol is considered generally safe by US and European authorities. There is only one documented case of toxicity caused by excessive alcohol intake. It is recommended to limit intake to 11.4 mg per pound (25 mg/kg) of body weight per day.
Health Effects of Propylene Glycol
There is a lot of conflicting information about the dangers of propylene glycol.

Some websites state it is safe, while others claim it causes heart attacks, kidney and liver failure and brain problems.

How Toxic Is Propylene Glycol?
The toxicity of propylene glycol is very low. It has not been found to cause cancer, damage genes or interfere with fertility or reproduction. Moreover, there are no reported deaths on record (1Trusted Source, 9Trusted Source).

In rats, the median lethal dose is 9 grams per pound (20 g/kg). Compare this to sugar, which has a lethal dose of 13.5 grams per pound (29.7 g/kg), or salt, which is just 1.4 grams per pound (3 g/kg) in rats (11, 12, 13).

After ingesting a food containing propylene glycol, about 45% of it will be excreted by the kidneys unchanged. The rest is broken down in the body into lactic acid (1Trusted Source, 14).

When consumed in toxic quantities, the buildup of lactic acid can lead to acidosis and kidney failure. Acidosis occurs when the body cannot get rid of the acid fast enough. It begins to build up in the blood, which interferes with proper functioning (10Trusted Source).

The main sign of toxicity is central nervous system depression. Symptoms include a slower rate of breathing, decreased heart rate and loss of consciousness (14).

Cases of poisoning may be treated with hemodialysis to remove the substance from the blood or by removing the drug or substance that contains propylene glycol (15Trusted Source).

However, toxicity is very rare. Most cases resulted from the use of very high doses of medication containing propylene glycol or unusual circumstances, such as one man who was ill and drank the contents of an ice pack (16Trusted Source, 17Trusted Source).

SUMMARY
Propylene glycol has very low toxicity. Poisoning rarely occurs, and it is typically due to high doses of medications that contain it.
Dangers for People With Kidney or Liver Disease
In adults with normal liver and kidney function, propylene glycol is broken down and removed from the blood fairly quickly.

On the other hand, in people with kidney disease or liver disease, this process may not be as efficient. This can lead to a buildup of propylene glycol and lactic acid in the bloodstream, causing symptoms of toxicity (9Trusted Source, 15Trusted Source).

Additionally, because there is no maximum dose limit for propylene glycol used in drugs, it is possible to receive very high doses in some circumstances (9Trusted Source).

One woman with kidney damage was treated for short breath and throat swelling with lorazepam. She received 40 times the recommended level of propylene glycol over 72 hours, resulting in acidosis and other symptoms of toxicity (18Trusted Source).

Critically ill patients often have impaired kidney or liver function and may also have an increased risk from prolonged or high-dose drug treatments.

For example, in one study, 19% of critical patients being treated with the drug lorazepam were observed to have signs of propylene glycol toxicity (19Trusted Source).

For people with kidney and liver disease, drug alternatives without propylene glycol may be used if needed. There is no evidence that dietary amounts are cause for concern.

SUMMARY
People with kidney or liver damage are not able to clear propylene glycol or lactic acid from the blood as effectively as healthy people. When receiving very high doses of it in medications, they have an increased risk of developing toxicity.
Dangers for Infants and Pregnant Women
Pregnant women, children and infants under four years of age have lower levels of an enzyme known as alcohol dehydrogenase. This enzyme is essential for the breakdown of propylene glycol  

Therefore, these groups may be at risk of developing toxicity if they are exposed to large amounts through medication.

Infants are at particular risk. They take up to three times as long to remove propylene glycol from their bodies and may be particularly sensitive to the effects on the central nervous system (9Trusted Source, 20Trusted Source, 21Trusted Source).

There are case reports of premature infants injected with large doses of vitamins containing propylene glycol that resulted in seizures (22Trusted Source, 23Trusted Source).

However, another study demonstrated that doses of up to 15.4 mg per pound (34 mg/kg) of propylene glycol over 24 hours were tolerated by young babies (24Trusted Source).

While these populations may be at increased risk of toxicity in the case of very high exposure from medication, there is no research indicating any harm from the amounts found in the diet.

SUMMARY
Young children and infants are not able to process propylene glycol as effectively as adults. Therefore, they are at risk of it building up in their bodies and developing symptoms of toxicity when exposed to high doses in medications.
Risk of Heart Attack
Some websites claim that propylene glycol increases the risk of heart disease and heart attacks.

It is true that when propylene glycol is injected in high amounts or too quickly, a drop in blood pressure and heart rhythm problems can occur (20Trusted Source).

Animal studies also demonstrate that very high doses of propylene glycol can rapidly decrease heart rate, cause low blood pressure and even cause the heart to stop (25Trusted Source, 26Trusted Source).

In one report, an 8-month-old child suffered loss of heart function and subsequent brain damage after being treated with silver sulfadiazine cream that contained propylene glycol. The cream was used for treating burns that covered 78% of his body (27Trusted Source).

In this case, the child received 4.1 grams per pound (9 g/kg) of propylene glycol, which is a very high dose.

In another case, a 15-month-old child was given oral doses of vitamin C dissolved in propylene glycol. He developed symptoms of toxicity, including non-responsiveness and irregular heart rhythms, but recovered after the vitamin solution was stopped (28Trusted Source).

While these reports may be concerning, it is important to note that in both these cases, toxicity occurred due to a high dosage of medication in a vulnerable age group.

The amount of propylene glycol found in a normal diet is not associated with any heart problems in children or adults.

SUMMARY
In vulnerable populations, high doses of propylene glycol from medications can cause problems with blood pressure and heart rate. However, there is no connection between heart problems and the amount of propylene glycol found in the diet.
Neurological Symptoms
There have been some reports of propylene glycol causing brain-related symptoms.

In one case, a woman with epilepsy developed repetitive convulsions and stupor due to propylene glycol poisoning from an unknown source (29Trusted Source).

Seizures have also been observed in infants who developed toxicity from injectable medications (22Trusted Source).

Additionally, 16 patients of a neurology clinic were given 402 mg of propylene glycol per pound (887 mg/kg) three times per day for three days. One of them developed severe unspecified neurological symptoms (30Trusted Source).

Very high amounts of propylene glycol were used in both of these studies, yet another study found effects at smaller doses.

Scientists observed that 2–15 ml of propylene glycol caused nausea, vertigo and strange sensations. These symptoms disappeared within 6 hours (31Trusted Source).

While these symptoms may sound scary, it should be emphasized that many different medications and substances can cause similar symptoms when ingested or given in quantities that cause toxicity.

There have been no reports of neurological changes due to propylene glycol in foods.

SUMMARY
At toxic levels, propylene glycol has been found to cause seizures and severe neurological symptoms. There have also been cases of nausea, vertigo and strange sensations.
Skin and Allergic Reactions
The American Contact Dermatitis Society has named propylene glycol as the 2018 Allergen of the Year (32Trusted Source).

In fact, between 0.8 and 3.5% of people are estimated to have a skin allergy to propylene glycol (32Trusted Source).

The most common skin reaction, or dermatitis, is the development of a rash on the face or in a generalized scattered pattern over the body (32Trusted Source).

Systemic dermatitis has been reported after eating foods and taking medications and intravenous drugs that contain propylene glycol (33Trusted Source, 34Trusted Source, 35).

One study of 38 sensitive people given propylene glycol by mouth found that 15 of them developed a rash within 3 to 16 hours (31Trusted Source).

In addition, propylene glycol can cause irritant contact dermatitis. In this case, a rash may develop in sensitive people when their skin comes into contact with products that contain it, such as shampoo or moisturizer (6Trusted Source).

People who already have skin conditions or sensitive skin are at particular risk of contact allergy to this additive (6Trusted Source).

For people with allergic dermatitis, it is best to avoid all sources of propylene glycol. For contact dermatitis, avoid products containing it that come into contact with the skin.

SUMMARY
Between 0.8 and 3.5% of people are allergic to propylene glycol. Common symptoms include a rash on the face or body.
How Can You Avoid It?
While propylene glycol is generally considered safe, you may still choose to avoid it if you are allergic or you simply want to reduce your intake.

It is found in many different food products and can be identified by checking the ingredients list. The names it may be listed under include:

Propylene glycol
Propylene glycol mono and diester
E1520 or 1520
Common foods include soft drinks, marinades and dressings, cake mix, frosting, popcorn, food coloring, fast foods, bread and dairy products (6Trusted Source, 35).

Unfortunately, if propylene glycol is used as a carrier or solvent for another additive, such as flavor or color instead of a direct ingredient, it may not be listed on the food label (36).

However, the majority of foods containing it are highly processed junk foods. By consuming a fresh, healthy, whole foods diet, you can avoid most sources without too much trouble.

You can also check the labels of cosmetic products, though avoiding it may be difficult. There are several helpful websites that can help you identify which products contain it.

If you have an allergy to propylene glycol, it is important to let your doctor or pharmacist know about it before taking certain medications. An alternative can usually be found.

SUMMARY
To avoid propylene glycol in foods, read labels and look for it as an ingredient or as the additive number E1520. Use online sources to help identify hygiene products that contain it. For medications, ask your doctor or pharmacist.
The Bottom Line
Propylene glycol is a useful chemical found in a wide variety of products across the food, drug, cosmetic and manufacturing industries.

While there are cases of toxicity from very high doses of medication, it is overall considered a very low-toxicity substance.

A small percentage of people are allergic to propylene glycol and may need to avoid products containing it.

Yet for most people, the amounts regularly found in food products are considered safe.

Keep in mind that most of the foods containing propylene glycol are highly processed junk foods. A fresh, whole foods diet will naturally contain lower amounts of this additive.

Propylene glycol is a synthetic liquid substance that absorbs water. Propylene glycol is also used to make polyester compounds, and as a base for deicing solutions. Propylene glycol is used by the chemical, food, and pharmaceutical industries as an antifreeze when leakage might lead to contact with food. The Food and Drug Administration (FDA) has classified propylene glycol as an additive that is “generally recognized as safe” for use in food. It is used to absorb extra water and maintain moisture in certain medicines, cosmetics, or food products. It is a solvent for food colors and flavors, and in the paint and plastics industries. Propylene glycol is also used to create artificial smoke or fog used in fire-fighting training and in theatrical productions. Other names for propylene glycol are 1,2-dihydroxypropane, 1,2-propanediol, methyl glycol, and trimethyl glycol. Propylene glycol is clear, colorless, slightly syrupy liquid at room temperature. It may exist in air in the vapor form, although propylene glycol must be heated or briskly shaken to produce a vapor. Propylene glycol is practically odorless and tasteless.

CDC-ATSDR Toxic Substances Portal
Propylene Glycol is a propanediol that exists as a clear, colorless and hygroscopic liquid and consists of propane where the hydrogens at positions 1 and 2 are substituted by hydroxyl groups. Propylene glycol is used as an organic solvent and diluent in pharmaceuticals and many other industrial applications.

NCI Thesaurus (NCIt)
Thick odorless colorless liquid. Mixes with water.

Molecular Weight of Propylene Glycol:    76.09 g/mol      2.1   
XLogP3 of Propylene Glycol:    -0.9    Computed by XLogP3 3.0   
Hydrogen Bond Donor Count of Propylene Glycol:    2     
Hydrogen Bond Acceptor Count of Propylene Glycol:    2     
Rotatable Bond Count of Propylene Glycol:    1     
Exact Mass of Propylene Glycol:    76.052429 g/mol      2.1   
Monoisotopic Mass of Propylene Glycol:    76.052429 g/mol      2.1   
Topological Polar Surface Area of Propylene Glycol:    40.5 Ų     
Heavy Atom Count of Propylene Glycol:    5     
Formal Charge of Propylene Glycol:    0     
Complexity of Propylene Glycol:    20.9     
Isotope Atom Count of Propylene Glycol:    0     
Defined Atom Stereocenter Count of Propylene Glycol:    0     
Undefined Atom Stereocenter Count of Propylene Glycol:    1     
Defined Bond Stereocenter Count of Propylene Glycol:    0     
Undefined Bond Stereocenter Count of Propylene Glycol:    0     
Covalently-Bonded Unit Count of Propylene Glycol:    1     
Compound  of Propylene Glycol Is Canonicalized    Yes