MONTEREY, CALIF. – It’s only found in 2%-3% of allergy cases. So Because, a dermatologist told colleagues, it’s so common.
Dr. Joseph F. Fowler Jr.
“If you’re allergic to it, it’s tough to stay away from it,” said Joseph F. Fowler Jr., MD, clinical professor of dermatology at the University of Louisville (Ky.) in a presentation about contact dermatitis at the annual Coastal Dermatology Symposium.
Indeed, the synthetic compound PG is found in skin care products and cosmetics, coated pills, topical medications such as corticosteroids, foods (including bread, food coloring, and such flavorings as vanilla extracts). “It’s in every topical acne product I know of,” and is even in brake fluid and so-called nontoxic antifreeze, he said. (Propylene glycol shouldn’t be confused with the poisonous toxin ethylene glycol, which also is found in antifreeze.)
Patients can be tested for allergy to PG, Dr. Fowler pointed out, but it’s important to understand that it can trigger an irritation reaction that can be mistaken for an allergic reaction.
Dr. Fowler offered the following tips related to contact dermatitis and allergens. Be aware that metals, topical antibiotics, fragrances, and preservatives are most likely to cause allergic contact dermatitis. According to 2016 figures on allergen prevalence from the North American Contact Dermatitis Group (NACDG), allergy to the metal nickel is the most common (16%); followed by neomycin (9%); fragrance mix I, a mixture of fragrances used in allergen testing (9%); bacitracin (8%); and myroxylon, also known as balsam of Peru, which is used for a variety of purposes in food, medicines, and fragrances (7%).
These are followed by the metal cobalt (6%); the preservatives quaternium 15 and formaldehyde (both 6%); para-phenylenediamine, also known as PPD, which is used in hair dye (5%); and the fragrance mix II (5%), another mix of fragrances used in allergen testing.
Dr. Fowler cautioned that nickel can trigger an intense body-wide allergic reaction in children with atopic dermatitis. “In this situation, it’s really good to be compulsive and tell parents to absolutely keep that person away from nickel as much as humanly possible,” he said.
Keep an eye out for allergens that aren’t on the NACDG list, which includes 70 items. According to Dr. Fowler, more than 20% of his patients were positive to allergens not on the NACDG list.
Contact dermatitis is as common in children as in adults and can even be more common in children. An Italian study published in 2012 found that 70% of children aged 1-15 years tested via patch test were allergic to at least one allergen, a number that’s similar in adults (Dermatitis. 2012 Nov-Dec;23[6]:275-80). There are wide disparities in reported levels of children who are allergic to nickel, cobalt, and myroxylon, Dr. Fowler said.
The T.R.U.E. Test patch test system has value, compared with standard patch tests, but beware of its limitations, he advised. T.R.U.E. is easy to use and requires no prep time, he said, but the number of allergens is limited. By contrast, his clinic mostly uses the Finn Chambers on Scanpor tape system, which can test for many more allergens and is cheaper if used at least 5-10 times a month.
He cautioned that T.R.U.E. could miss the cause of contact dermatitis as often as 39% of the time, as demonstrated in one study of children undergoing patch testing (Arch Dermatol. 2008 Oct;144[10]:1329-36). However, he said, the T.R.U.E test has value in detecting allergies to nickel, methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), and neomycin (J Am Acad Dermatol. 2001 Dec;45[6]:836-9).
Consider patch testing in a child with eczema if the eczema is not in normal atopic areas, it spreads beyond normal areas, it doesn’t respond to usual treatments, or it begins later than 5 years of age.
And, Dr. Fowler added, it’s fine to perform patch testing on patients who are taking antihistamines, tumor necrosis factor–alpha inhibitors, NSAIDs, or methotrexate.
Dr. Fowler disclosed consulting for IntraDerm, serving on speakers bureaus for SmartPractice and Regeneron/Sanofi, and serving as an investigator for companies that include AbbVie, Allergan, Bayer, Dow, Galderma, Johnson & Johnson, Eli Lilly, Merck, Regeneron, SmartPractice, and Valeant (now Bausch).
The meeting was jointly presented by the University of Louisville and Global Academy for Medical Education. This publication and Global Academy for Medical Education are both owned by Frontline Medical Communications.