In the winter, dormant poison ivy and oak plants may lose all of their leaves and berries. It can be difficult to tell if the plants are still alive. Even with dead poison ivy, all parts of the plants, including the roots and stems, contain rash-causing urushiol. Urushiol will remain intact and does not evaporate, even after the plants die.
A common way of getting poison ivy in the winter is by handling firewood. Be cautious of any cut trees that have leafless vines wrapped around them as you could touch dead poison ivy without realizing it. Burning poison ivy or oak can be quite dangerous as it can result in inhalation of urushiol causing a severe rash that spreads systemically throughout the body.