How Does Poison Ivy Work?

poison ivy and rash

Did you know just how many American citizens suffer from the effects of the poison ivy on an annual basis? According to certain medical associations, it’s more than 40 million people! It’s no wonder, seeing as the plant is notoriously hard to spot among other garden plants that are common in most areas. Plus, this pesky plant can easily mask its presence among other weeds. Though, once you do come into contact with the poison ivy, you’ll know it’s happened; you’ll probably get a horribly itchy rash. So, why does this happen? We’ll go into the details right here, so stay tuned!

The Poison Ivy 101
Why does the poison ivy represent one of the most irritating poisonous plants you can come across? The culprit for its effects is the chemical found in every poison ivy plant, named urushiol. If you’re thinking this is a weird name, it’s because it’s not Latin, like most names of plants are - but Japanese. This is also the substance that basically triggers the same reaction once people come into contact with poison sumac and poison oak plants. In fact, all of the aforementioned plants come from the same biological family - scientists call them the Anacardiaceae.

Poisonous Plants
Upon coming in contact with poison ivy, people often develop an itchy, red rash caused by the plant. Generally, people who work in the garden suffer from this; though hikers, bikers, paddlers, and kids playing at the edge of the lawn often come into contact with it as well. If you touch any part of the plant, including the stems, roots or leaves, you’ll definitely be in for a rash; possibly accompanied by blisters.

An astounding majority of people have an allergic reaction once they come in contact with urushiol found in the poison ivy; some 85%, in fact! And only trace amounts are enough to trigger the allergic reaction; as little as one-billionth of a single gram! Naturally, you’ll hear some people boasting that they’ve touched the plant a bunch of times without suffering any consequences. However, this doesn’t mean that they’re immune to the effects of the poison ivy. In some cases, the allergy isn’t triggered unless the subject is exposed to the plant a couple of times.

So, as urushiol is present in pretty much the entirety of the poison ivy; root, stem, and leaf, you’d do well to completely avoid this plant. As for where you can find the plant, as you may know already - it’s pretty much present throughout the entire continental United States. And while the plant usually has leaves grouped in threes, this is only a general rule of thumb. Be careful, as it may grow to have as many as five leaves in a single group!

Finding The Poison Ivy
So, how else can you identify this poisonous plant, apart from its leaves? Firstly, you need to know that there are two different kinds of poison ivy. Indeed, we differentiate between the Eastern and Western types. The former climbs and grows as a ground vine or a shrub, while the latter is only found in the form of ground vine or shrubbery.

When it comes to poison oak, we’ve got the Atlantic and Pacific kinds. The Pacific is only found in the state of California, and it’s quite similar to the Eastern poison ivy; it grows as a climbing vine, shrubbery, or ground vine. There isn’t much to differentiate the Pacific poison oak and the Eastern poison ivy, apart from the fact that the former has no hairs; while the Eastern ivy attaches to surfaces via “hairs”. The Pacific poison oak, conversely, climbs by wrapping itself around trees. That’s possibly why you won’t find it growing on buildings like the Easter poison ivy would.

Eastern poison ivy can be found in a wide variety of habitats. In fact, it can thrive in both dry and wet areas. In the West, the plant is found in dry areas with a lot of heat. However, the poison ivy avoids the heat by growing in the shade of trees, and near water. On the other hand, the Eastern poison ivy appears in both the dryest and the wettest areas; we’re talking about an incredibly adaptable plant.

Poison Ivy And The Immune System
Next up, we’ll have a look at just how the poison ivy has an effect on your immune system.

First of all, a quick recap; as you probably know already, the immune system of the human body is there to protect us from any viruses, bacteria, and any other type of foreign invaders that may cause us harm and sickness. But if you touch the poison ivy with your bare skin, you’ll have an immune response - referred to as dermatitis. This is the same kind of response the body has with hay fever; in that case, your immune system is having an overreaction to pollen.

Going back to the poison ivy, though - the urushiol gets under your skin (no pun intended), where it is broken down. Then, your immune cells spot the urushiol derivatives and recognize them as a threat. That’s why they send a signal, in the form of inflammatory cytokines; these serve to bring white blood cells “to the scene of the crime”. Upon reaching the spot on your skin, the abovementioned white blood cells morph into macrophages. And the macrophages are there to devour the foreign intruder, but the process also damages your regular skin tissue - which is what causes the inflammation you see.

The specific allergic reaction people have to the poison ivy is referred to as “delayed hypersensitivity”. Conversely to immediate hypersensitivity, the former may not emerge for a couple of hours, or possibly even days. That’s why some people don’t have an inflammatory reaction the very first time when they come into contact with the poison ivy. However, they do develop a reaction once they’ve been exposed to it a couple of times. The sensitivity of each individual varies, so people may have a slightly different, or differently timed reaction to the plant.

Editor's Note
This is a guest article by those knowledgable folks at Gardener's Path.