As someone who is allergic to poison ivy, I know how miserable the itchy rash it causes can be. The rash occurs 12-72 hours after exposure to poison ivy, poison oak, and poison sumac. It is always best to recognize the plant and avoid it, but if you think your child has been exposed, immediately wash the exposed skin with warm, soapy water, and also wash their clothes. If a rash develops, mild cases can be treated with hydrocortisone cream and calamine lotion. Oral antihistamines may also help with the itching. More extensive rashes may need to be treated with a prescription medication such as prednisone. Contrary to popular belief, the rash itself is not contagious and does not spread, although it may seem to do so due to a delayed reaction.