A rash caused by skin contact with an allergen is referred to by the medical term "allergic contact dermatitis." Allergic contact dermatitis occurs when the body identifies a foreign substance as being a potential threat and responds by releasing chemicals called histamines. Histamines increase blood vessel permeability, allowing fluid containing white blood cells to flow into areas affected by the allergen. This results in the swelling, redness and itch characteristic of an allergic skin rash. Several vining plants have been identified to cause allergic reactions.
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The poison ivy plant, known by the botanical name Rhus radicans, is the most well-known vine that commonly causes allergic contact dermatitis. The red, itchy blisters of a poison ivy reaction result when the skin brushes up against the leaves of the plant, leaving a sticky resin called urushiol deposited on the skin’s surface. Urushiol exposure can also result from touching the stem or root of the plant, or even from brushing against another object that has touched the plant, such as firewood, or a pet’s fur, according to the Mayo Clinic.
Urushiol remains persistently on an object until it is washed, so clothing that has been exposed to urushiol, put away, and worn a year later can cause a poison ivy rash.
The poison ivy plant is commonly found forests. It can grow as a vine, plant or bush form. It has green leaves that may turn red in autumn. These leaves occur in sets of 3, and may have saw-toothed, or smooth edges.
Poison oak, or Toxiconfrendron diversilobum, takes three different forms: shrub, ground cover or vine. It is part of the same family of plants as poison ivy, and similarly, has leaflets grouped in sets of three. The surfaces of poison oak leaves are shiny, and the edges can be lobed or smooth. Poison oak leaves are green in the spring and summer and turn red in autumn.
As with poison ivy, poison oak contains urushiol. Humboldt University notes that most of the population is allergic to this resin, with only 10 to 25 percent of people unaffected by urushiol exposure.
DermNet NZ reports that the vines that bear the cute, fuzzy fruit known as kiwis can cause a no-so-cute case of allergic contact dermatitis. The kiwi plant, or Actinidia chinensis, contains an allergen called proteinase actinidin. In addition to allergic contact dermatitis, contact with kiwis and kiwi vines can cause urticaria, or hives, and irritant contact dermatitis, which results when an irritant disrupts the skin's natural protective barrier.