Toxicodendron: A painful summer institution

A Latin Refresher: Toxicodendron means Poisonous Tree Toxicodendron radicans is Poison Ivy Toxicodendron toxicarium is Poison Oak Toxicodendron vernix is Poison Sumac

Leaves are primarily trifolate

Urushiol is the allergenic component Urushiol is the allergenic component. It is a kind of oil found in the leaves, stems, and roots.

It is found in other foodstuffs:

Urushiol penetrates the epidermis and binds to Langerhans cells Urushiol penetrates the epidermis and binds to Langerhans cells. In sensitized patients, previously stimulated helper T cells recognize the urushiol and initiate an immune response.

Time Course Symptoms develop in 4 to 96 hours. Symptoms can peak up to 2 weeks after exposure. The fluid in the blisters is NOT antigenic. The rash doesn’t spread. Continued infection is due to re-exposure. Allergic responsiveness wanes with age, particularly in those with milder reactions.

More information about urushiol: It binds to cell membranes. After an hour or so, it won’t wash off. It is stable at high temperatures. So, burning poison ivy or poison oak disperses through the air with it’s allergenic potential intact. It can cause inflammation and irritation of respiratory tissues. It is stable in general, and can remain on fomites for a long time. Some say up to 5 years! It can waft on a summer breeze and cause a reaction in the very very allergic. Some native American tribes use it to remove warts. Only homo sapiens react to it.

Looks like:

Not…

Complications Edema, especially when the face or genitals are affected. Respiratory difficulties. Bacterial super-infection, primarily with gram positive organisms.

Treatment Calamine lotion and oatmeal baths. Sedating anti-histamines. High potency topical corticosteroids. (But not on mucous membranes or in skin folds.) Systemic glucocorticoids if: face or genitals are affected; more than 10% of the body is involved; reaction is severe. Start with 1 mg/kg of prednisone, give it for a week, and then taper over the next two weeks. NB: Avoid topical benadryl, which causes a reaction all it’s own.