I know a guy who had poison ivy all over most of his body as a teenager. An old timer came by his house and took him and his Dad to a real cold creek. The old timer had him get in the real cold water up to his neck and stay in it for over 30 minutes until his skin was fixing to turn blue. The poison ivy rash healed within two to three days. The guy is 47 years old now and has been immune to poison ivy ever since.