Propylene Glycol Avoidance Diet
Updated: Sep 9, 2019
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. 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 (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.
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.
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.
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.
Reading labels will definitely help. If PG is used in a product, it will be listed on the ingredient list, which makes it easy to search for.
When I'm concerned that PG may be contributing to a patient's rash, I recommend avoidance for 6 weeks. That's because it can take up to 6 weeks for the skin to improve, even after complete elimination from the diet.
It's hard to 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.
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 may act as a trigger. I suspect that the amount needed to trigger a rash is different for every patient with a PG allergy. For example, I've had some patients who are able to ingest capsules of medication (that contain PG) without any problems. But some of these same patients can't handle certain foods.
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.