Many of us heard "leaves of three, let it be" as children running wild through the suburban jungle, so we would know which plants were poison ivy. Just touching poison ivy, or touching something it touched, will give you a nasty rash.
Use lemon juice to relieve the itching or rash from poison ivy. Apply directly to the affected areas. The acid reduces the rash and surrounding redness the same way it clears up pimples. Avoid scratching -- the more you bother the rash, the longer it will take to heal.