Contact with sap from poison ivy, oak, and sumac causes a rash in most people. It begins with redness and swelling at the contact site, then becomes intensely itchy. Blistering appears within hours or a few days. The typical rash is arranged as a red line on an exposed area, caused by the plant dragging across the skin. The rash usually lasts up to two weeks.
Above: Poison Ivy Skin Rash Picture Above: A severe case of Poison Ivy skin rash Above: An innocent looking Poison Ivy can cause severe skin rashes. SKINIPEDIA, your Skin Encyclopedia
The rash is caused by skin contact with the oils (resin) of these plants. Smoke from burning these plants can cause the same reaction. The oils usually enter the skin rapidly. It is rarely spread from person to person.