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Published on April 29, 2021

Poison ivy poison oak sumac skin rash

Poison ivy, poison oak, poison sumac…oh my!

How to identify and treat common plant rashes

Whether you enjoy hiking, doing yard work or just being outside, it's likely that you'll eventually encounter some of the Tri-state Area's least favorite plants: poison ivy, poison oak and poison sumac. Learn how to spot the plants and what to do if you accidentally touch them.

What do poison ivy, poison oak and poison sumac look like?

There's a reason for the saying "leaves of three, let it be." That's because both poison ivy and poison oak commonly have three green leaves per stem. Poison sumac, on the other hand, can have anywhere between seven and 13 leaves. See the differences here.

Why do poison ivy, poison oak and poison sumac cause a rash?

The plants are part of the Toxicodendron genus—a family of plants characterized by its mixture of oil and resin known as oleoresin. Within this oleoresin is a chemical called urushiol. Urushiol is allergenic, so much so that a rash develops in up to 90 percent of people who come into contact with as little as 50 micrograms of it. For reference, that's less than one grain of table salt!

How can I tell if I have a rash from urushiol?

A urushiol rash usually has a linear (line-like) appearance. The rash may appear flat and red or as large blisters. What it looks like specifically, and how much area the rash covers, depends on how much poison ivy, poison oak or poison sumac you touched or if you previously were ever exposed to urushiol.

Will my rash spread from itching it?

Some people believe that itching or scratching a urushiol rash can make it spread on the body. This isn't true. If it seems like poison ivy, poison oak or poison sumac rash is spreading, this is because of the amount of urushiol you touched.

For example, if you get a lot of urushiol on one part of your body, your immune system will recognize this large dose first and blossom a rash there more quickly. Other areas where you encounter less urushiol will take longer for a rash to pop up, making it seem like your rash is growing over time. (It can take up to three weeks for a rash to appear if you've never come into contact with urushiol before.)

Regardless, the next time you are exposed to urushiol, your body will already have immune cells waiting to make a rash. This means that with each subsequent exposure to urushiol, your rash will likely appear faster and be worse.

So, urushiol rashes aren't contagious?

That's right. While poison ivy, poison oak and poison sumac rashes aren't contagious, urushiol can be spread by contaminated surfaces. Think dogs or cats. The oleoresin that contains urushiol can sit on an animal's fur without causing a rash and then transfer to you.

What should I do if I touch poison ivy, poison oak or poison sumac?

If you have a known exposure to the plants, flush the area with plenty of water. And be sure to act quickly. After 10 minutes, you've missed your window of opportunity to rinse off and a rash will form. It's also important to keep in mind that soap and alcohol can expand the area of oleoresin on your body, so don't immediately use these substances. Stick to water.

What else can I do to treat a urushiol rash?

As for at-home treatments, taking a cool bath and applying calamine lotion can help. If your rash covers a lot of skin, talk to your healthcare provider about your options. They can help you understand the most effective treatments, including a prescription oral steroid that's taken for two to three weeks.

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