This patient was allergic to a chemical called propylene glycol-and it turns out it was in her moisturizer, her medicated cream, and even her salad dressing
One of my patients (let’s call her “Mrs. Smith”) had a perplexing food allergy. She had a persistent rash on her arms, and she noticed that it would worsen whenever she ate a particular brand of salad dressing. Mrs. Smith underwent prick testing, but the testing didn't reveal any food allergies. She also had blood testing for food allergy, which didn't show any reactions either.
Because her rash was so persistent, she finally had patch testing done. The patch testing showed that she was allergic to a particular chemical called propylene glycol (PG). This chemical was in several of her skin care products. It was even in one of her medicated steroid creams.
Surprisingly for her, it was also in her salad dressing.
What is propylene glycol and where is it found?
Propylene glycol (PG) is a very interesting chemical. It's used in antifreeze and brake fluid. It's also used in many skin creams, It’s even found in many prescription medicated creams, such as the steroid creams that are used to treat eczema and dermatitis.
It's also used (surprise!) in certain processed foods.
How to avoid propylene glycol in your skin care products
If you are allergic to propylene glycol, the first step in avoidance is to make sure that none of your skin care products contain it. This means checking your soaps, lotions, creams, hair care, makeup, shaving cream, and more. After that, you'll have to check any medicated creams or ointments that you have purchased OTC or been prescribed by your doctor.
If you'd like to see some products that are free of propylene glycol, please see my handout.
This handout has my short list of products that do not contain any propylene glycol (and also don't contain any of the common triggers of allergic skin reactions, such as synthetic and natural fragrance additives, formaldehyde preservatives, or methylisothiazolinone.)
Why would a food contain propylene glycol?
PG is a synthetic liquid that’s a little bit thicker than water. It doesn’t have any taste, scent, or color, which makes it easy to add to food products.
Even more than that, it has several important properties that make it helpful for manufacturers when creating food products. PG is generally recognized as safe and non-toxic, so manufacturers often use it in their food products.
It’s an emulsifier, which means it helps dissolve oil into water. That makes it perfect for keeping salad dressings in a bottle from “separating.”
It can help a product retain moisture, so you might see it in marshmallows.
It keeps products from clumping, so you might see it in grated cheese.
It’s a preservative that extends the shelf life of foods, which means it might be useful in all sorts of products.
It’s often used as a “carrier”, because it can help dissolve other additives such as flavorings or dyes. Flavoring pastes used in baking often use propylene glycol. Flavoring packages for snow cones are often dissolved in a base of propylene glycol.
It’s often used to help the “mouthfeel” of a food, for example to make it feel thicker and more substantial.
What foods contain propylene glycol?
PG is found in many different types of processed foods because of all of these helpful manufacturing properties. (It's not found in nature, so we're only concerned with processed foods).
I've seen it listed as an ingredient in
Salad dressings
Tartar sauce
Mustard
Barbecue sauces
Packaged snack cakes and donuts
Snack foods such as French-fried onions or potato sticks
Frosting
Cake mixes
Snow cone flavorings
As a base for flavoring additives in baking
Many other food products
Does coffee have propylene glycol?
Many flavored coffee bean brands use PG as a chemical solvent in their production process, so there may be some residual PG in the coffee. However, this is probably only a very small amount and for most people shouldn’t be a concern.
Does dairy have propylene glycol?
I don’t worry about dairy as a source of PG. Although some sources state that dairy cows may be treated with PG, it’s unclear if the resulting milk contains trace amounts of the compound. Even if there were trace amounts, most patients seem to be OK with trace amounts.
How can I find out if a product contains propylene glycol? Will propylene glycol always be listed as an ingredient?
The answer to this question is almost always. The easiest way to search for propylene glycol in a product is to read the ingredient list. It’s almost always listed. Below are some other names for propylene glycol. [For a full listing of other names for PG, please see this list.]
Propylene glycol
1,2-Propanediol
1,2-Dihydroxypropane
Isopropylene glycol
In general, propylene glycol will be listed as an ingredient. However, there are a few exceptions. If you’re highly sensitive, you need to be aware of the exceptions.
Here's one exception: if PG is used as a component of a flavoring, it may not be listed separately as an ingredient.
For example, if a processed food lists "flavorings", then PG may have been used as a component of that flavoring.
What this means is that if you're highly sensitive to PG, you'll need to watch out for foods that list natural flavors, natural flavorings, artificial flavors, or artificial flavorings.
If I have a propylene glycol allergy, do I really need to stop eating it? Do I have to avoid all foods that contain propylene glycol?
Not everyone who is allergic to PG on their skin will have problems with foods.
Some of my patients only have problems when they come into contact with PG on their skin. Other patients react when they eat foods that contain PG: their rash gets worse when they eat these foods.
At this time, we don't have extensive data on how many people who are allergic to PG on their skin will also react to PG in foods.
That’s why, for my patients, I usually take a stepwise approach.
First, have you noticed that processed foods seem to make your rash worse? If so, then stop eating any foods that contain PG.
If you’re not sure, we always start by focusing on skin care products and medicated skin creams first. For my patients, I’ll create a list of skin care products that they can use that completely eliminates their exposure to PG.
This list of hypoallergenic skin care products has multiple options that patients can use. If a product contains PG, it is listed next to the product in parentheses.
If my patient doesn’t improve after 8 weeks of avoiding PG in their topical products, then we move on to avoiding it in foods.
Finally, if their rash still isn’t better, then I recommend that they avoid it in their medicated capsules. That’s usually the last step, because it’s more involved and often isn’t going to be necessary.
If I start avoiding PG, how quickly will I notice changes in my skin?
When I'm concerned that PG in foods may be contributing to a patient's rash, I recommend complete avoidance for eight weeks. That's because it can take up to eight weeks for the skin to improve, even after complete elimination from their skin care and from their diet.
How much propylene glycol would I need to consume to cause a reaction?
How much PG would a patient need to consume before it triggers a rash?
From experience, the amount needed to trigger a rash is different for every patient with a PG allergy.
Many of my patients who are allergic to PG in skin creams and medicated creams don't have any issues with PG in foods at all.
Other patients seem to be fine with a small amount of PG in their food, but then notice that their rash worsens if they go over a certain “threshold.”
Other patients have told me that even a small amount of PG in their foods seems to aggravate their rash.
If I have a propylene glycol allergy, do I need to avoid capsules or medications that contain PG?
Again, the response seems to vary quite a bit from patient to patient.
Some of my patients are able to ingest capsules of medication (that contain PG) without any problems. But some of these same patients can't handle certain foods.
Others notice that certain capsules with PG seem to make their rash worse.
As with so much in medicine, everyone's different.
How do you test for an allergy to propylene glycol?
If you think back to my patient Mrs. Smith, she had negative food testing even though she was ultimately allergic to PG. Why did her food allergy testing not pick up on this allergy?
Many people don't realize how complex food allergies, and food allergy testing, can be. There's a lot we still don't know about food allergies.
There are different types of food allergies and food allergy tests
One thing that is known is that there are different types of food allergies, and they can cause different types of reactions.
For some people, a food allergy may cause lip swelling.
For others it may cause a skin rash, or trouble breathing, or gastrointestinal issues.
Some people experience a single symptom, while others experience a combination of symptoms.
Other body systems may be involved too.
Because there are different types of food allergies, there are different types of food allergy tests.
For some food allergies, we know the exact immune system pathway that's involved.
For other types of reactions, we don't.
When the pathway is known, we can develop a test for it.
For example, certain food allergies are IgE-mediated, which means that skin prick tests or blood tests can identify the culprits.
In Mrs. Smith’s case, her allergy was caused by T cells, which means that patch testing can be used to identify the culprit.
Systemic contact dermatitis is one type of food allergy that is diagnosed by patch testing
Mrs. Smith had developed a particular type of food allergy called systemic contact dermatitis.
In this type of allergy, a person eats a food.
Hours, or even days later, a rash begins on their skin.
This type of allergy is mediated by a part of the immune system called T cells.
We test for this type of allergy by patch testing.
What causes systemic contact dermatitis?
In most cases, we don’t have a clear explanation for why someone develops this kind of allergy.
What we do know is that there are several triggers of systemic contact dermatitis.
One of the most common occurs in some people who are allergic to fragrance additives in their skin care products. Some of these patients will react to balsam of peru and will then experience a worsening of their rash after they eat cinnamon, tomatoes, citrus, or other related foods.
Propylene glycol is another trigger for systemic contact dermatitis
Formaldehyde is another type of trigger
Nickel in foods can also be a trigger, especially for some patients with hand eczema
Is propylene glycol dangerous? A few common misconceptions about propylene glycol
Is propylene glycol dangerous? In the amounts used in creams and in processed foods, the answer is no. The FDA has deemed PG to be GRAS: generally recognized as safe.
Is propylene glycol toxic to humans? Again, in the amounts commonly used, the answer is no.
Is propylene glycol a steroid? No, PG is not a steroid. However, it can be found in many steroid creams. (Steroid creams are also known as topical corticosteroids.) It’s used because of its special properties, which include the ability to help active ingredients penetrate into the skin more effectively.
Does propylene glycol turn into formaldehyde? No.
Is propylene glycol a carcinogen? No, the studies to date have not found it to be a carcinogen.
Basically, PG is not a “bad” chemical. The main issue is that if you become allergic to it, it can be tricky to avoid, mainly because it’s used so widely.
What is the difference between propylene glycol and ethylene glycol?
Propylene glycol (PG) and ethylene glycol are both compounds that decrease the freezing point of water.
These properties make both PG and ethylene glycol useful as preservatives and anti-freezing agents.
However, ethylene glycol is highly toxic to humans and must be completely avoided.
PG, on the other hand, is considered minimally toxic. That’s why it’s approved for use in foods
What is the difference between propylene glycol and polyethylene glycol? Is propylene glycol the same as polyethylene glycol?
Polyethylene glycol (PEG) sounds like it would be very similar to propylene glycol, but it’s chemically very different.
Patients who are allergic to propylene glycol are not considered allergic to polyethylene glycol.
The Bottom Line: For some patients who are allergic to propylene glycol in their skin care products or medicated creams, avoidance of propylene glycol in foods may help with their dermatitis.