Phytodermatitis Slides 41 through 45

Reprinted with permission from the American Academy of Dermatology. All rights reserved. Please note that the slides are very large JPEG files that will take up to 6.5 minutes to view or download using a 28.8 kbps modem.

Allergic Contact Dermatitis

Allergic contact dermatitis requires previous sensitization to low molecular weight compounds in a plant. Not everyone develops an allergic reaction to these compounds. The most common plant causing this reaction is poison oak or ivy. The large family of plants, Compositae, contain chemicals called sesquiterpene lactones, which are sensitizers and irritants. Most of these rashes are chronic, eczematous rashes as compared to the severe blisters that develop from contact with the poison oak or ivy plants. Allergic contact dermatitis is the least common type of plant reaction except for problems with poison oak or ivy.

Slide 41

The swelling and erythema on the face is from airborne contact with the sawdust of pine and fir.

Airborne contact dermatitis from sawdust

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Slide 42

The resin in the red pine (Pinus resinosa) contains turpentine and colophony which causes allergic contact dermatitis in loggers and woodworkers.

Red pine (Pinus resinosa)

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Slide 43

Needles and pinecone of red pine (Pinus resinosa).

Needles and pine cone of red pine (Pinus resinosa)

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Slide 44

The sawdust of the Western red cedar (Thuja plicata) can cause asthma and allergic contact dermatitis. The allergens are quinone compounds.

Western red cedar (Thuja plicata)

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Contact Urticaria or Pharmacologic Injury

Urticaria (hives) develops with contact of the plant or plant material. The reaction can be allergic or non-allergic. In the non‑allergic type reaction, irritant hairs on the surface of the plant enhance penetration of the pharmacological materials into the skin. These chemicals include acetylcholine, histamine and serotonin. The reaction can last for a few hours.

The allergic type reaction can result in swelling of the mucous membranes (eyes, lips and throat) with generalized urticaria. Individuals with atopic dermatitis are more prone to this type of reaction. Most of these reactions are caused by latex proteins, garlic, onions, tulips and lilies in susceptible people.

Slide 45

The nettles plant (Laportea canadensis) has sharp calcified tips on the stinging hairs of the plants. When the plant penetrates the skin, the tips break secreting histamine, acetylcholine and serotonin.

Nettles (Laportea canadensis)

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