Look, But Don’t Touch

Poison Ivy vine and leaves (photos by Dianne Machesney)

If you’re like 85% of the human race, you’re allergic to Poison Ivy.  Some people are so sensitive it puts them in the hospital.  Others get no rash for years and then their bodies “switch on” one day.  Even if you’re part of the 15% who won’t react it’s best to be careful, if not for yourself then for others.

I’m not extremely allergic to poison ivy but I’m careful to know exactly what it looks like because the rash is so uncomfortable.  The rash is caused by an oil found in the plant’s leaves, roots, stems, vines and berry hulls called urushiol.  Humans are allergic to it; birds and other mammals are not.  Deer, horses, cattle and goats eat poison ivy without ill effect.  Birds eat its berries.  Bees pollinate its flowers.  Only humans are plagued by it.

Amazingly you can come in contact with urushiol and not know it for up to two days.  You can pick it up by brushing against the plant, touching clothing or tools that have touched the plant or its roots, or petting an animal that walked through poison ivy.  (How sneaky!)

If you know you’ve touched poison ivy, you can prevent the rash by a liberal dousing of the affected area with rubbing alcohol then copious water, but you have to do it within 4-6 hours of contact.  Otherwise, the oil works its way into your skin and breaks down.  A day or two later there’s nothing to wash off but your body begins a huge over-reaction:  red, swollen skin and spreading blisters.  This is not because the oil is still present but because your body is freaking out.

The good news is that if you can avoid contact with poison ivy for many years, your body may forget the allergy and allow you a mild exposure every once in a great while.  But you have to remain vigilant.  Frequent exposure restarts the allergy.

So how do you identify this annoying – even dangerous – plant?

“Leaflets 3, let them be” is one of the clues.

  • A poison ivy “leaf” is actually a compound of three lightly toothed leaflets on a long stem.
  • The center leaflet has a stem of its own and is symmetrical (both halves of the leaf are the same shape).
  • The left and right leaflets have no stems, are connected at their base and are asymmetrical (lopsided).
  • All three leaflets are attached to the plant on a long stem that floats them out toward you, temptingly within reach.
  • New poison ivy leaves are very shiny but for full grown leaves that’s not a good clue.  The older leaves are far less shiny than mulberry leaves.

Poison ivy’s greenish flowers and white berries grow in the leaf axils (see photo on right).  Not all of the plants bloom.  They must be two years old to do so.

Though poison ivy is classified as a vine you’ll often find it growing from gnarled woody stems.  Sometimes the stems support so many leaves that the plant looks shrubby.  When the stems find something upright to lean on they throw out aerial roots and climb as vines that look hairy (see photo on the left).  The vines and stems never have thorns.

In autumn the leaves turn red, dry up and fall off.  The vines become bare and the woody stems stick up from the ground like thin gnarly fingers.  Interestingly the dead leaves don’t cause a rash because the plant pulls the urushiol back into itself as it prepares for winter.

Now that you’ve read about it, are you ready for a quiz?  Click on the photo above and see if you can recognize the poison ivy in the linked photo.

Or try this quiz on the Poison Ivy website.   (Also see the Comments for more links and advice.)


(photos by Dianne Machesney)

13 thoughts on “Look, But Don’t Touch

  1. I’m one of those “lucky” people who will get not only the rash, but giant hives if exposed. (Poison oak too.) The worst case I ever got was when I picked up and cuddled the neighbor’s cat, who had apparently taken a roll in a patch of it. Definitely no fun!

    Growing up I was ragingly jealous of one of the kids in my neighborhood who was one of the 15% who has no reaction to it. I refused to believe him until he demonstrated one day by grabbing a bunch of it and rubbing it up and down his arms. I thought for sure he’d pay for such a brazen action–nope! Not even the faintest red spot.

  2. Perhaps you could post some pictures of what isn’t poison ivy? I can recognize it, but seem to be the minority.

  3. Does anyone know someone locally who is able to remove LARGE PI plants in trees? .. someone who knows what they are doing but isn’t outrageously expensive. We have discovered two really large plants that are probably the origin of the entire population in our yard, most of which we have been able to control. I checked online but the nearest person listed was in Philadelphia. I have read all the hints about how to remove it yourself… 🙂 Thanks!

  4. I had poison Ivy several times over the period of about 2 years (1994-1995). My first encounter was in the wooded area behind the playground behind my old elementary school. Me and 3 of my friends were looking for balls that any of the kids might have lost over the fence during recess and at some point I apparently scraped my leg on a stick and simultaneously or subsequently got poison ivy in the same place so I actually had it in the scrape (as well as all over my legs). I got it 3 or 4 times over the next couple years, but (thankfully) have not had it in about 14 years.

  5. Another clue to ID is that the center leaf is symetrical (both halfves match \/ ), the side leaves are asymetrical (only one half matches |/ ). We’ve also found that jewelweed (touch-me-not) is a good natural antidote within those first few hours. Just squeeze the juice from the leaves on the contact area.

  6. I don’t know anything about removing poison ivy from trees, but if I had that problem, I would take an axe to the lower parts of the vine and see if the rest just dies off. Almost all of the plants in a given area are connected. Too bad there isn’t a virus that you could give them. Or a poison ivy borer. I have some in my yard and am looking to get a spray for it.
    For Jewelweed, you can also crush up the stalks of the plants, they contain even more juice than the leaves.

  7. Oh, and here are more tips.
    Wear clothing that covers as much skin as possible.
    Wear disposable gloves under work gloves to prevent the oil from seeping through the work gloves to your hands.
    Wear a sweatband. If urushiol gets into your sweat you don’t want sweat to drip down your face… it makes me itch to think of it.
    Wash everything afterward but be prepared to throw away the work gloves.
    DON’T BURN POISON IVY! The oil will get into your lungs.

  8. Thanks for the hints – and yes, I had read those tips, including the axe, although even that needs to be gentle so the sap/oil does not spray around. My concern is that the [hopefully] dead plant will still be up there and still able to inflict attacks on anyone below. I have used a spray on the plants that I can reach safely.

  9. Just remembered a trick I learned in my toxicology class back in college. You can put some weed killer in a plastic bag and then place the bag over the leaves so that the chemicals get absorbed into the plant and kill it. I tried it with some success on some very stubborn vines (not poison ivy) that were growing all over the fence and garage at my moms old house. I imagine it would also work if you severed the stem and placed a baggie of weed killer on both ends. A baggie of weed killer on the root end would theoretically allow the chemical to be drawn into the roots and kill the whole plant.

  10. This was very interesting to read. I unfortunately got it a couple weeks ago and It’s still not completely gone away. Luckily it is finally drying up now. It itches like no other itch I’ve ever experienced.

  11. Kate ~

    Thank you, thank you so much for the information. I now know that what I have in my back yard is definitely poison ivy, and can warn guests appropriately. It also helps to explain why what I’m spraying it with doesn’t seem to make much of a dent. I understand that it’s difficult to kill. While I am not a fan of chemicals, it may be time for Round-up, maybe even the concentrate. Thanks again.

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