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.
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.
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 ( 1 ).
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.
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 ( 6 ).
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, 7 ).
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, 6 ).
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.
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 ( 9 ).
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 ( 9 ).
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 ( 9 ).
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 ( 10 ).
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.
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 ( 1 , 9 ).
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 ( 1 , 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 ( 10 ).
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 ( 15 ).
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 ( 16 , 17 ).
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 ( 9 , 15 ).
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 ( 9 ).
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 ( 18 ).
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 ( 19 ).
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 ( 1 , 9 , 20 ).
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 ( 9 , 20 , 21 ).
There are case reports of premature infants injected with large doses of vitamins containing propylene glycol that resulted in seizures ( 22 , 23 ).
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 ( 24 ).
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 ( 20 ).
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 ( 25 , 26 ).
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 ( 27 ).
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 ( 28 ).
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 ( 29 ).
Seizures have also been observed in infants who developed toxicity from injectable medications ( 22 ).
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 ( 30 ).
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 ( 31 ).
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 ( 32 ).
In fact, between 0.8 and 3.5% of people are estimated to have a skin allergy to propylene glycol ( 32 ).
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 ( 32 ).
Systemic dermatitis has been reported after eating foods and taking medications and intravenous drugs that contain propylene glycol ( 33 , 34 , 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 ( 31 ).
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 ( 6 ).
People who already have skin conditions or sensitive skin are at particular risk of contact allergy to this additive ( 6 ).
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.
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