Urushiol is toxic oil that causes skin-allergy. The oil is produced by the toxicodendron plants (poison ivy, poison oak, poison sumac). The exposure to urushiol occurs by touching such plants or any chemical that contains the oil. The oil does not spread so washing the affected area will save rest of the body. The rashes usually appear within a day and will stay for weeks. The allergy gets worse in repeated recurrences. The smoke produced by burning plants containing the oil is also toxic. Some fire-fighters catch the allergy due to exposure to the oil.

The affected person gets rashes, blisters, swelling, papules and vesicles. The severity of the allergy varies in people. Nearly 80percent people get the allergy when exposed to fifty micrograms of the oil. However more sensitive persons can catch the allergy from only 2 micrograms of oil.

Direct contact with urushiol should be avoided. If the contact is made skin should be washed with soap or detergent. Anthistamines are effective in treating the rashes produced by the oil. Cold water or sitting in cool room does not reduce the allergy but only reduces the itchiness and inflammation. The fluid from the allergic blisters does not spread the allergy.

According to sources approximately 50 million people in United States catch the allergy every year. Poison oak is the dominant culprit held responsible for it. People usually uproot the Poison Ivy plants to avoid possible contact. Poison Ivy is found in rural areas of southern and western parts of United States.