The single most common cause of allergic reaction in the United States is that of Poison Ivy. In the Midwest it grows as a crawling or climbing vine. In the far Northern and Western areas of the U.S. and Canada, it grows as a shrub. All parts of the plant can cause severe skin inflammation, itching, and blisters. The roots, stems, leaves, berries and flowers are all toxic; producing a volatile oil called urushiol. It is rendered inactive by water; …