Poison ivy, poison oak, and poison sumac are closely related species, all three containing a colorless or slightly yellow oil called "urushiol." Skin contact with this oil causes an allergic reaction. While each of these three plants contains a slightly different type of urushiol, they are so similar that children sensitive to one type will react to all three. The entire plant contains urushiol and is therefore poisonous: leaves, berries, stalk, and roots.
Urushiol is easily transferred from the plant to an object and then to a child, so anything that touches these poison plants—clothing, gardening tools, a pet's fur, athletic equipment, sleeping bags—can be contaminated and cause poison ivy in anyone who touches the object. Urushiol remains active for up to one year, so any equipment that touches poison ivy must be washed. The smoke from burning poison ivy is especially toxic to the skin of the face, the eyes, or the lungs. it will also irritate the throat if eaten.
As the leaves die in the fall, the plant draws certain nutrients and substances (including the oil) into the stem. But the oil remains active, so that even in winter it may cause a rash if the broken stems are used as firewood, or the vines on a Christmas wreath.
Despite persistent folklore, poison ivy is NOT spread by scratching open blisters or by skin-to-skin contact. Only the oil can trigger a reaction. However, doctors recommend that a child not touch the blisters, because any remaining oil on the skin that has not been washed off could be transmitted to another part of the body. Scratching blisters also may cause infection from germs on the skin surface.
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