In North America, it is estimated that 80% of the population is sensitive to poison ivy (eastern and western) and its cousins plants (poison sumac, eastern and western poison oaks). The degree of sensitivity can vary significantly over the life of a person and from one person to another. For example, children are often more sensitive than adults and people with thicker skin and strong hair have less severe reactions. The American Academy of Dermatology estimates there are up to 50 million cases of urushiol-induced dermatitis annually in the United States, accounting for 10% of all lost-time injuries in the United States Forest Service.
Non allergic people? (the lucky ones)
Because urushiol is contained in a varnish widely used in Asia, obviously Asian people are not worried about this allergy. People of these regions are exposed to urushiol since centuries and millennia, so their bodies are accustomed to this substance. Indians of America, that originate from Asia, are also not allergic to urushiol. White people of North America are exposed to urushiol since 1 to 3 centuries. Apparently, it’s not long enough. The miscegenation can increase or decrease the allergic reaction of person to urushiol.
About 20% of the people in North America are not allergic to urushiol, but there’s no guarantee one person won’t become sensitive. People can develop the allergy after exposure to the plants. Repeated exposures to urushiol can make a person more and more sensitive. So a person living in city since birth and moving to countryside can develop this allergy slowly, being exposed repeatedly to poison ivies or poison oaks.
The toxic effects of urushiol are induced by an immune response. Urushiol acts as a hapten, and is combined with proteins on exposed skin cells and elicit the production of antibodies that bind specifically to it. Affected proteins interfere with the immune system’s ability to recognize these cells as normal parts of the body. This immune response is directed towards the urushiol derivatives (pentadecacatechol) bound in the skin proteins, attacking the cells as if they were foreign bodies.
The irritant element in poison ivy is urushiol, which is present in the sap of this plant. The name urushiol comes from the Japanese word urushi, which is a varnish made from the sap of a tree. Thus, all parts of the poison ivy are poisonous to the touch: leaves, stems, roots and fruits. Urushiol is a powerful allergen which penetrates the skin cells in less than 5 minutes. It is a stable compound that does not evaporate and its toxicity may persist for several months on dead plants and objects that have been contaminated.
Various contacts with urushiol
The sap, contained within the plant, is released when the plant is damaged. The leaves are more fragile, and more likely to poison us. In this sense, a skin contact with an intact plant will produce no reaction.
Animals do not react to urushiol but a sensitive person will be poisoned if it is in contact with an animal that moved in poison ivy. This is an indirect contact. Urushiol can also reach us by air if the plants are burned in a fire or crushed and thrown by a lawnmower or trimmer. Personally, when I stopped mowing the lawn, my reactions to poison ivy fell significantly.
Videos about urushiol