Poison Ivy
Toxicodendron radicans

 

Poison Ivy contains a chemical that can cause the skin of persons sensitive to it to develop a red, itchy rash and even erupt in blisters. Urushiol is the active ingredient in Poison Ivy that causes the rash and irritation. It is present in all parts of the plant, but particularly in the sap.  People vary in their sensitivity to urushiol.  Some have no problem with it and others experience severe allergic reactions.  This can also vary over the life of a person.  You might be unaffected as a child and become sensitized with repeated exposures. 

The clinical name for the skin irritation caused by Poison Ivy is Rhus Dermatitis.  It usually starts as itching and small blisters within a few hours after exposure.  Depending on how strong the exposure was and/or how sensitive the person is, that may be all there is to it.  However, it may develop into an inflamed, swollen rash with open, weeping sores that persists for up to two weeks.   Severe cases may require a visit to the doctor.  Urushiol is absorbed into the skin within three minutes of exposure. An important fact to remember is that the urushiol can travel on your clothes or the fur of your pets, so remember to wash them too if you suspect they were in contact with Poison Ivy.

Poison Ivy grows in a number of different ways:

As a ground cover - It can creep across the ground surface and make a knee-high thicket of foliage. 

As a skinny free-standing "shrub" - It can grow in the open with one stem and only a few side branches.  It may be up to ten feet tall in this form, and this is the form that people call Poison Oak.  

As a vine - Using thin, brown, aerial roots, it can attach itself to the side of a tree or other object and reach high into the sky.  This is the form where it reaches it greatest size.  It is not uncommon to find vines as thick as your arm growing up the side of large trees.