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Allergic Contact Dermatitis From Usnic Acid Produced by Lichenized Fungi

J. C. MITCHELL, MD

Arch Dermatol. 1965;92(2):142-146.

Abstract
Two forest workers affected with allergic contact dermatitis, which occurred only during work in forest areas, showed positive patch test reactions to lichens containing usnic acid and to isolated usnic acid.

Lichens are plants composed of fungi living in symbiosis with algae. Usnic acid, one of the lichenic acids which accumulates in lichenized fungi, is a monobasic acid with dibenzofuran structure and antibiotic properties. Dibenzofuran is chemically related to furocoumarans.

Lichens are plentiful in temperate zone forests and allergy to usnic acid represents some part of the "cedar-poisoning" problem in British Columbia. Geographical distribution of lichens containing usnic acid suggests that allergy to usnic acid will be found to be more common than presently recognized.

Author Affiliations
VANCOUVER, BRITISH COLUMBIA

From the Department of Medicine (Dermatology), University of British Columbia, Vancouver. Clinical Assistant Professor.

Footnotes
Accepted for publication April 23, 1965.

Presented at the Institute of Dermatology, St. John's Hospital for Diseases of the Skin, London, Dec 2, 1964.

Reprint requests to the Department of Medicine (Dermatology), University of British Columbia, Vancouver 8 (Dr. Mitchell).

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