KOLOA, HAWAII — Next time a patient's skin disease isn't improving despite what ought to be effective topical medication, consider the possibility of occult allergic contact dermatitis caused by a chemical in the vehicle base, Dr. David E. Cohen urged at the annual Hawaii Dermatology Seminar sponsored by the Skin Disease Education Foundation.
This is a surprisingly common occurrence. Indeed, well over half of the 32 most common contact allergens are chemicals contained in medical vehicles, according to the results of patch testing conducted in 2001–2002 by the North American Contact Dermatitis Group (NACDG) in nearly 5,000 patients with suspected allergic contact dermatitis.
Fragrance chemicals are the group of allergens that most often cause contact dermatitis due to topical medication vehicles, followed by preservatives, said Dr. Cohen, director of allergic, occupational, and environmental dermatology at New York University.
Fragrance chemicals are also the No. 1 cause of allergic contact dermatitis in the United States as a whole, as shown by the most recently published NACDG patch test results.
Leading the way is balsam of Peru, a liquid derived from a plant bark that consists of more than 180 aromatic compounds. Balsam of Peru tied with neomycin for second place on the NACDG allergen list, with each eliciting positive allergic patch test reactions in 11.6% of the 4,913 patients tested. Only nickel sulfate was a more frequent allergen, with a 16.7% positive test rate. Occupying third place on the NACDG list was fragrance mix, with a 10.4% rate.
When patch testing is performed on the general population rather than in patients with suspected allergic contact dermatitis, up to 4% of subjects prove sensitive to fragrance chemicals.
The preservative systems employed in topical medication vehicle bases are complicated. They fall within two major categories: the formaldehyde releasers and the nonformaldehyde preservatives.
Two of the six widely used formaldehyde releasers cracked the NACDG top 10: quaternium-15 (9.3%), and formaldehyde (8.4%). Methyldibromoglutaronitrile (Euxyl K400) was the nonformaldehyde preservative with the highest positive patch test rate, at 5.8%.
“Euxyl K400 is in a lot of cosmetic product bases. It's so important an allergen that in the European Union they're pretty much not allowing it in leave-on products, only in wash-on/wash-off products,” according to Dr. Cohen.
Parabens is a nonformaldehyde preservative commonly used in topical corticosteroid bases, as is methylchloroisothiazolinone/methylisothiazolinone (Kathon CG). Parabens gets a lot of negative publicity, yet its positive patch test rate was a mere 0.6% in the NACDG study. There are far worse offenders. “If you look at Kathon or Euxyl K400 or quaternium-15, they're 3, 6, or 9 times more likely to be allergens than parabens,” the dermatologist continued.
He highlighted three emerging underappreciated contact allergens as worthy of special mention:
▸ Benzalkonium chloride: This quaternary ammonium preservative is now used in five times more products than thimerosal, including contact lens solutions, cosmetics, and shampoos.
▸ Cocamidopropyl betaine: It's an amphoteric surfactant present in more than 600 personal care products. It's especially popular for use in shampoos, soaps, and facial cleansers because it is nonirritating to the eyes.
▸ Propylene glycol: Like benzalkonium chloride, it can cause not only allergic contact dermatitis, but irritant contact dermatitis marked by nonimmunologically related burning and stinging.
The Skin Disease Education Foundation and this news organization are wholly owned subsidiaries of Elsevier.
Parabens gets a lot of negative publicity, yet there are far worse offenders. DR. COHEN