Propylene Glycol Avoidance Diet
Updated: Sep 13
One of my patients 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. She 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 propylene glycol (PG). This particular chemical was in several of her skin care products. It was even in one of her medicated steroid creams. Surprisingly, it was also in her salad dressing.
Propylene Glycol: Used in Skin Care, Brake Fluid, and Processed Foods
Propylene glycol (PG) is a very interesting chemical. It's used in antifreeze and brake fluid. It's also used in many skin creams, and it's also found in many prescription medicated creams. It's also used (surprise!) in certain processed foods.
It's not a "bad" chemical, but for people who develop an allergy to it, it can be difficult to avoid.
Food Allergy: Different Types, and Different Tests
Why did the food allergy testing not pick up on this allergy? Because there are different types of food allergies.
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.
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.
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.
Systemic Contact Dermatitis: One Type of Food Allergy
In this case, my patient had developed a particular type of food allergy called systemic contact dermatitis. In this type of allergy, a person eats a food, and hours, or even days later, a rash begins on their skin. This type of allergy is mediated by T cells, and we test for it by patch testing.
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 with a worsening of their rash after they eat cinnamon, tomatoes, citrus, or other related foods.
In the case of PG allergy, some (not all) people who are allergic to it on their skin may also react when they eat it. In other words, they may develop a worsening of their rash when they eat foods that contain PG.
Foods that Contain Propylene Glycol
What foods contain this chemical? It's found in different types of processed foods. (It's not found in nature, so we're only concerned with processed foods). I've seen it in salad dressings, barbecue sauces, cake mixes, and snow cone mixes. I've also seen it used as a base for flavoring additives in baking, as well as other food products.
While Processed Foods That Contain Propylene Glycol Often List It As An Ingredient, Be Aware of the Exceptions
If PG is used in a product, it is usually listed on an ingredient list (but not always). For those that are 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. If you're highly sensitive to PG, that means you'll need to watch out for foods that list natural flavors or flavorings, or artificial flavors or flavorings.
If you're allergic to PG, you should avoid processed foods that list propylene glycol in the ingredient list. Just be aware that foods that contain flavorings may (or may not) also contain PG, even if it's not listed separately on the ingredient list.
For Those Who Are Allergic, Avoiding PG In Their Skin Care And Foods May Not Help Right Away
When I'm concerned that PG may be contributing to a patient's rash, I recommend avoidance for 8 weeks. That's because it can take up to 8 weeks for the skin to improve, even after complete elimination from their skin care and from their diet.
If you're allergic to PG, we definitely recommend avoiding it in your skin care. What we don't know is if you'll need to avoid eating it. In other words, we do not know if consuming PG will worsen a rash in a particular patient. At this time, we don't have good data on how many people who are allergic to PG on their skin will also react to PG in foods.
How Much Propylene Glycol Would You Need to Consume To Trigger a Rash?
PG is also used in some oral medications and capsules. This brings up another question.
We don't know what level of PG in a food or medication would act as a trigger. From experience, I suspect that the amount needed to trigger a rash is different for every patient with a PG allergy. And many of my patients who are allergic to PG in skin creams and medicated creams don't seem to have any issues with PG in foods at all.
When it comes to medications, 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. As with so much in medicine, everyone's different.
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.
Dr. Rajani Katta is the author of Glow: The Dermatologist's Guide to a Whole Foods Younger Skin Diet. To receive future updates on preventive dermatology and the role of diet, sign up here.