All parts of poison oak contain poisonious oil, Urushiol. Urushiol is highly potent and will cause severe rash and discomfort. The oil binds with skin proteins within 10-15 minutes, making it hard to remove. Rashes can form anywhere from 6 hours to 5 days after exposure.
Tecnu poison oak soap and other products are available at most drug stores. Please make sure the product is safe and will not exacerbate or irriate symptoms. Good luck!