Watch out! This stuff is bad news and it’s on the Nature Trail. You’ll find it mostly in among the English Ivy and climbing on a few trees.
It will cause an itching, irritating, and sometimes painful rash in most people who touch it. In extreme cases, a reaction can progress to anaphylaxis. 15% to 30% of people have no allergic reaction, but most people will have a greater reaction with repeated or more concentrated exposure.
Poison Ivy affects the skin by way of an oil, urushiol, which is a clear liquid compound in the plant’s sap. Immediate washing with soap and cold water or rubbing alcohol may help prevent a reaction. Hot water should not be used, as it causes pores to open up and admit the plant oils.
Learn to identify it and stay clear. Here are three helpful rhymes which describe the characteristic appearance of poison ivy:
- Leaflets three; let it be
- Hairy vine, no friend of mine
- Berries white, run in fright
There are plants that look similar:
Virginia creeper (Parthenocissus quinquefolia) vines can look like poison ivy. The younger leaves can consist of three leaflets but have a few more serrations along the leaf edge, and the leaf surface is somewhat wrinkled. But the best way to be sure is to count the leaves, most Virginia creeper leaves have five leaflets.
- Box-elder (Acer negundo) saplings have leaves that can look very similar to those of poison ivy, although if you look carefully, you’ll see that there are more than three leaves on the small branches.
Kudzu, which we all know is an invasive species in the southern United States. Like poison ivy, it has three leaflets, but the leaflets are bigger than those of poison ivy and are underneath have hairy margins.
Did you know that:
- Poison ivy can grow as ground cover, as a climbing vine reaching very high and growing quite large, and as a shrub.
- If your pet rolls in poison ivy, the oils can be transferred to you. Clothing, tools, and other objects that have been exposed to the oil should be washed to prevent further transmission.
- Urushiol oil can remain active for several years, so handling dead leaves or vines can cause a reaction.
- You should never burn poison ivy. If poison ivy is burned and the smoke then inhaled, a rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty. 
- A poison ivy rash usually develops within a week of exposure and can last anywhere from one to four weeks, depending on severity and treatment. In rare cases, poison ivy reactions may require hospitalization. 
- As much as we dislike it, birds feel differently and eat the berries, which is how it can spread to our yards and natural areas.
References and Additional Information
 Mayo Clinic: Poison Ivy Rash
 CDC: Poisonous Plants
 Wikipedia: Toxicodendron radicans