And the Allergen Winner Is: Propylene Glycol!

Jeannette Y. Wick, RPh, MBA, FASCP
Published Online: Friday, January 19th, 2018
Every year, the American Contact Dermatitis Society (ACDS) holds a contest that results in awards similar to the Rotten Tomatoes award for movies. It crowns its Allergen of the Year. This year, the winner is an ingredient common to many cosmetics, topical skin products, foods, and medications.

Propylene glycol (PG) has been a commercial product in the United States since the 1930s. It became a very common product in air fresheners when a researcher’s work indicated it could sterilize air. PG is a useful, flexible multipurpose chemical. It's used as an anticaking agent, antimicrobial, dough strengthener, emulsifier, flavoring, humectant, solvent, stabilizer, and text Dreiser. It's a good skin conditioning vehicle. And, it's odorless.

This particular contact allergy is important to understand for 2 reasons. First, PG is a wily character because it's been difficult to determine how often it is a contact allergen. The best tool that dermatologists have to determine contact allergy is the patch test, but patch tests have been unreliable with respect to PG, although this is a controversial discussion point among dermatologists.

Second, manufacturers have used PG more and more over the years, and it is present in an extremely large number of products (in 2012 it was listed in 5676 products and ACDS estimates it is a component of approximately 38% of products ). At the present time, dermatologists estimate that PG allergy ranges from 0.8% to 3.5%, but it is much more likely to cause allergy when it's in aqueous solution. In that case, allergy rates range from 10% to 30%.

Clinically, retail health providers need to know a few facts:
  • Patients are most likely to develop PG contact dermatitis on the face, with approximately 26% of cases diagnosed in that location.
  • In 24% of cases, the allergy manifests as a generalized/scattered pattern.
  • More than half of allergies occur pursuant to use of personal care products, and deodorants, bath salts, and bath oils have the highest concentration.
  • Topical corticosteroids represent more than 18% of reactions.
  • PG is an infrequent cause of occupational dermatitis.
  • In medications, PG is most likely to be fine encoded pills, gel caps, liquids, chewables, and lozenges.
Patients who have atopic dermatitis may be at highest risk of this allergy.

Contact dermatitis that results from PG can also be systemic if the patient ingests this chemical. Although this is rare, it's important to know. Most patients will develop rash within 3 to 16 hours of ingestion. PG is ubiquitous in food, especially packaged foods, breads, canned foods, bacon, dairy products, condiments, and artificial flavor extracts and food colorings. It is present in almost all fast food.

The retail health care provider's role once this allergy is identified is to educate patients about reading labels carefully, as avoidance is the best way to prevent reactions.

Jacob SE, Scheman A, McGowan MA. Allergen of the Year: Propylene Glycol. Dermatitis. 2017 Nov 10. doi: 10.1097/DER.0000000000000315. [Epub ahead of print]
McGowan MA, Scheman A, Jacob SE. Propylene Glycol in Contact Dermatitis: A Systematic Review. Dermatitis. 2017 Oct 23. doi: 10.1097/DER.0000000000000307. [Epub ahead of print] 

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