Allergic Contact Dermatitis

Question 1

Cross-reactivity vs Co-reactivity

Answer 1

Cross-reactivity: reaction to two or more allergens because of shared chemical features leading to similar recognition by the immune system.

• Ester anesthetics such as benzocaine are known to cross-react with the hair dye paraphenylenediamine
• Patients sensitized to ethylenediamine, an ingredient in topical medications, may manifest systemic contact dermatitis following exposure to hydroxyzine
• Neomycin and gentamicin are both aminoglycoside antibiotics
• Patients sensitized to urushiol in Toxicodendron plants may react on exposure to the ginkgo fruit

Co-reaction: reaction to two or more allergens due to concomitant sensitization or simultaneous exposure, without any immunologic basis.

• Nickel and cobalt, commonly found together in the same metal products•Neomycin and bacitracin, which are often combined in topical antibiotics, but unrelated chemically.

Question 2

Urishiol/Asteraceae

Answer 2

The predominant allergen in plant members of the Asteraceae/Compositae family is SQL. This family is composed of edible plants such as chicory, sunflower, and artichoke as well as decorative plants like chrysanthemum and dahlias

Question 3

Acrylates

Answer 3

The contact allergen in question is in the acrylate family, specifically methyl methacrylate, which polymerizes to form a plastic material. The acrylates have many uses, and methyl methacrylate in particular is used to form acrylic bone cements in orthopedic surgery, medical spray adhesives, and dental prosthetics. The dermatitis formed by methyl methacrylate is usually in areas of exposure and in classic cases, appears as itching, burning, scaling, fissuring, and similar eczematous changes. Purpuric changes have also been described. Chronic exposure can result in paresthesias that take months to resolve. Unfortunately, methyl methacrylate readily crosses surgical gloves. It passes through latex within one minute and vinyl/nitrile within three minutes. Double gloving does not decrease methy methacrylate permeability, but the addition of a layer between the gloves (such as water) may decrease permeability fourfold.

The formaledhyde releaser quaternium 15 is not a major cause of hand dermatitis in dentists. The allergen ethylenediamine cross-reacts with hydroxyzine. Paraphenylenediamine is a black dye used in henna tattoos.

Question 4

Latex

Answer 4

Latex is more likely to cause a type I hypersensitivity reaction (immunologic contact urticaria), but repeat exposures may result in eczematous hand dermatitis. Common cross-reactors of latex can be remembered with the mnemonic “BLACK Panther”:

Bananas, Latex, Avocados (A), Chestnuts, Kiwis, Passionfruit. Health care workers are at an increased risk of latex allergy.