Click on the pictures (in number order) below to learn more about the urushiols’ effect on humans. Who gets it? What causes the symptoms? Poison ivy Poison oak 1 2 3

Who gets it? About 50% of people will get poison ivy or poison oak when they brush up against a plant in nature.

Does age matter? In one study urushiol containing leaves were rubbed on the backs of individuals of various ages, and the following was found.

What occupations get it? It affects those who spend significant time in the forest the most. For example 10% of the days taken off by lumberjacks is due to urushiol allergies, and 1/3 of forest firefighters have gotten poison oak or poison ivy by inhaling urushiols during a fire.

What causes the symptoms? When urushiols are transferred to the skin, they will remain there for 3 days if not washed off. Because urushiols are small lipophilic molecules they can easily penetrate the epidermis of the skin or the layers of the respiratory tract and cause a delayed type hypersensitivity reaction (DTH). The next three slides illustrate the 3 steps of these reactions.

Afferent Phase Because urushiols are lipophilic they are able to pass through the membrane of the Langerhan cells (LC) in the epidermis of the skin. The urushiols are displayed on the surface of the cell by an MHC I molecule. Some of the LC cells then travel to the lymph nodes (see picture) where T cells will be activated toward the urushiols in those with an allergy to them.

Efferent phase The activated T cells reach the epidermis within about 48 hours and they begin releasing cytokines, which recruits more T cells and causes dermatitis. This picture shows severe dermatitis caused by poison ivy.

Resolution phase Ultimately, T cells and macrophages release cytokines that will stop the response. The whole process can take up to 3 weeks in severe cases.

What else is affected? The same immune reaction occurs when urushiols are inhaled, with sometimes severe respiratory reactions. When urushiols enter through the skin they also enter the blood stream and have been found in many other organs, but no allergic reaction occurs there.

Sources Information source McGovern, T.W. Toxicodendron Dermatitis; Identification, Immunological Mechanisms, Diagnosis, and Treatment. Professional Educations Services Group Photo sources pfaller-en.html (Photo slide 6) McGovern, T.W. Toxicodendron Dermatitis; Identification, Immunological Mechanisms, Diagnosis, and Treatment. Professional Educations Services Group (All other photos and chart)