Poison ivy

Poison ivy, or more properly Toxicdendron radicans, is a plant which produces a sap that causes an allergic rash and itch on contact with skin in about 70-85% of all human beings. The plant is found throughout North America and thrives in sunny areas. The rash is characterized by small bumps which develop into fluid filled blisters. If the plant is ingested, similar blistering will occur in the upper digestive tract. Neither of this type of exposure is generally dangerous, athough hospitalization may be necessary if exposure is heavy. However, the sap survives burning and if contaminated smoke is inhaled, it can cause life-threatening inflammation of the lungs.
A poison ivy rash will resolve itself in about four weeks. Treatment is symptomatic. When exposure is realized, washing with a strong detergent is recommended, although care should be taken not to spread even the diluted sap to unaffected areas. Topical cremes, oatmeal baths and baking soda help relieve the itching. Antihistamines can help reduce the inflammation. Ice packs are recommended to ease the oozing from the blisters.
Poison ivy is often difficult to distinguish, and a series of mnemonics have been developed to identify it:
#"Longer middle stem; stay away from them." This refers to the middle leaflet having a visibly longer stem than the two side leaflets and is a key to differentiating it from the similar-looking fragrant sumac.
#"Leaves of three; let it be."
#"Hairy vine, no friend of mine"; Poison ivy vines are very poisonous.
#"Raggy rope, don't be a dope!" Poison ivy vines on trees have a furry "raggy" appearance. This rhyme warns tree climbers to be wary. Old, mature vines on tree trunks can be quite large and long, with the recognizable leaves obscured among the higher foliage of the tree.
#"One, two, three? Don't touch me."
#"Berries white, run in fright" and "Berries white, danger in sight."
#"Red leaflets in the spring, it's a dangerous thing." This refers to the red appearance that new leaflets sometimes have in the spring. (Note that later, in the summer, the leaflets are green, making them more difficult to distinguish from other plants, while in autumn they can be reddish-orange.)
#"Side leaflets like mittens, will itch like the dickens." This refers to the appearance of some, but not all, poison ivy leaves, where each of the two side leaflets has a small notch that makes the leaflet look like a mitten with a "thumb". (Note that this rhyme should not be misinterpreted to mean that only the side leaflets will cause itching, since actually all parts of the plant can cause itching.)
#"If butterflies land there, don't put your hand there." This refers to the fact that some butterflies land on poison ivy, since they are not affected, which provides them protection as their predators avoid eating the plant.
#"If it's got hair, it won't be fair."
Toxicodendron radicans at Wikipedia
Part of this article was copied from Wikipedia under its Creative Commons license.
Poison ivy