Poison ivy (Toxicodendron radicans) is not a true ivy, but rather a member of the cashew family (Anacardiaceae) which also includes poison oak, poison sumac, mango, cashew, and pistachio. Three out of four Americans are sensitive to poison ivy, and many are allergic to other members of the family as well. Poison ivy has dark green leaves, each of which is divided into three 2-4 inch smooth sided leaflets. In summer the leaflets are shiny green, but they turn red or orange in fall before dropping off in winter. This is a thornless vine whose larger stems are woody. The vines may scramble across the ground, rooting along the way, or cling to tree trunks with hairlike aerial rootlets. If there’s nothing to climb on, poison ivy can stand erect without support for a foot or two.
The similar looking Virginia Creeper (Parthenocissus quinquefolia) also has a woody stem, aerial rootlets, and red leaves in autumn, but its leaves are divided into five leaflets. A harmless plant mimicking one that’s not so harmless!
Poison Oak (T. pubescens) is similar to poison ivy, but has thicker leaves that are hairy (not smooth), and is always an upright shrub, not a vine. It tends to occur in dry habitats.
Poison Sumac (T. vernix) is an uncommon wetland shrub or small tree that has 7-13 leaflets per leaf.
Poison ivy can spread and start new plants from underground rhizomes, adventitious rooting along the stem, and by seed. Poison ivy produces inconspicuous yellowish or greenish white flowers in summer that give rise to attractive white berrylike drupes in fall. The fruits are eaten by birds and small mammals which return the favor by spreading the seeds further than the plant could ever do by itself.
The active ingredient in poison ivy sap is called urushiol (pronounced yoo-ROO-shee-all). When urushiol touches the skin of susceptible folks, it causes contact dermatitis, an itchy red rash which often leads to blisters.
You cannot get the rash from simply brushing against poison ivy; you must actually break the stem, leaves or roots to release the urushiol. You can, however, get contact dermatitis from touching clothing, shoes, tools, or pets that have urushiol on them. (Your pets are immune to the effects of the toxin!) Even the smoke from burning poison ivy can cause symptoms internally as well as externally.
Scratching the poison ivy rash does not cause it to spread. You can’t spread the rash with the fluid that oozes from the blisters. Other people can’t catch the rash from you. By the time a rash has developed, the urushiol is gone and it’s your body responding.
If you think you might become exposed to poison ivy, you should wear protective clothing, including gloves, long sleeves, and long pants (be sure to wash them afterwards). If you’ve been exposed to poison ivy sap, you can reduce or even prevent a reaction if you act fast.
Rinse the affected area with rubbing alcohol (isopropanol) within 10 or 15 minutes after exposure.
The rubbing alcohol dissolves the urushiol which can then be rinsed away with soap and water. If you don’t have any rubbing alcohol, you can scrub and rinse, and scrub and rinse some more with soap or detergent and tepid (not warm) water. Warm water opens skin pores, allowing more of the toxin into the skin. This tends to move the sap around rather than dissolve it, so be thorough.
Treatments for poison ivy rash and blistering include any of several commercial poison ivy creams, Calamine lotion, hydrocortisone, or a simple paste of baking soda and water. These don’t cure the dermatitis, but they relieve the itching and help dry the blisters. For poisoning so severe that there are systemic symptoms, an antihistamine such as Benadryl can bring some relief. Your doctor will prescribe steroids or other medications for especially severe cases.
Here at Perfect Plants, when we see poison ivy growing around our gardens and yards, we get out the gloves and pull it up by the roots. If there’s more than we care to pull up, we treat it (carefully) with an herbicide that contains triclopyr, 2,4-D, or Glyphosate such as Ortho Max Poison Ivy®, Spectracide®, or Roundup Poison Ivy®. If you cut the stem and then apply the herbicide to the open stump, you can kill the roots and prevent further spreading from rhizomes.