What are the signs and symptoms of allergic contact dermatitis due to Anacardiaceae plants?

Updated: Jun 10, 2021
  • Author: Glen H Crawford, MD; Chief Editor: Dirk M Elston, MD  more...
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After an individual who is sensitized has contact with urushiol, an erythematous pruritic eruption typically develops within 2 days. If the skin is washed within 30 minutes of contact with the toxin, the eruption may be prevented. The time until eruption can be extremely variable. It is influenced by body site, allergenicity, the concentration and length of exposure, prior sensitization, and other host factors.

Involved areas demonstrate streaks of erythema and edematous papules; later, vesicles and bullae appear. The sequential appearance of lesions over different areas of the body may create the false impression of a spreading or infectious process. Poison ivy dermatitis may seem to spread because different concentrations of allergen contact skin sites of varied thickness. The allergen must travel through variable layers of the stratum corneum to reach the Langerhans cells, the antigen-presenting cells of the epidermis.

In some patients, asymptomatic and persistent black lesions may appear on the skin. These lesions are referred to as black lacquer spots. They occur where a sufficient amount of resin has been deposited to cause a vesicant reaction (the oleoresin is a vesicant at high concentrations). On rare occasions, severe reactions to poison ivy can cause erythema multiforme, [6] erythema scarlatiniform, or urticarial eruptions. Postinflammatory hyperpigmentation is common in dark-skinned individuals following a poison ivy eruption.

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