Keep this in mind if you went for a hike and came back with an angry-looking rash.

By Madison Yauger
June 28, 2021
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You've just spent a lovely day outdoors, perhaps working in your garden, or hiking a woodsy trail, when your leg starts itching. You look down and see a streaky red rash starting to form across the back of your calf, and come to the frustrating realization that you must have encountered a poisonous plant, and are having an allergic reaction.

The three likeliest culprits for skin irritation or rashes from outside plants are: poison oak, poison ivy, and poison sumac. According to the American Skin Association (ASA), poisonous plant reactions affect roughly 50 million Americans annually-that's because 85% of the US population is allergic to the oil that comes from these plants' sap.

Poison-Oak-Rash-AdobeStock_242565916
Credit: AdobeStock

Sometimes though, it's hard to determine what plant, exactly, is the cause of a rash on your body-especially if you didn't see what you came into contact with. Here's what you need to know about poison oak rashes specifically, including symptoms and treatment options.

What is poison oak-and why does it cause a rash?

Poison oak grows as a low shrub in the eastern and southern US, but it can also grow in tall clumps or long vines in the Pacific Coast, according to the US Food & Drug Administration (FDA). The plant has "fuzzy green leaves" that grow in clusters of three, and may also have yellow-white berries.

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Credit: AdobeStock

The sap from a poison oak plant-along with poison ivy and poison sumac plants-is what triggers the allergic reaction, that typically shows up a few hours to a few days after exposure. "The plant produces an oil called urushiol that can cause [a] rash in people allergic to it," Debra Jaliman, MD, a board-certified dermatologist and assistant clinical professor of dermatology at the Icahn School of Medicine at Mount Sinai, tells Health.

"When your skin comes in contact with the leaves of the plant, the urushiol touches the skin and elicits an immune response," Joshua Zeichner, MD, associate director of cosmetic and clinical research in dermatology at Mount Sinai Hospital, tells Health.

Urushiol is colorless and odorless, per the ASA, which means it's hard to determine when you've come into contact with it (oftentimes, the only way you'll know if once a rash appears). It's also important to know that you don't have to come into direct contact with poison oak to develop a rash-you can get it from simply touching something else that has come into contact with it. One example of this is if your pet touches poison oak or another urushiol-containing plant, they can spread it to you via their fur, says Dr. Jaliman.

What are the symptoms of a poison oak rash?

Generally speaking, the main symptom that comes after exposure to a poison oak plant (or other similar plants) is a red rash within a few days of contact, according to the Centers for Disease Control and Prevention (CDC). "The rash typically comes in streaks because it only develops in the areas [where] the leaves brush up against the skin," says Dr. Zeichner. "[But] if you touch the areas of skin exposed to the urushiol, you can actually spread it to other parts of the body through your fingertips."

Poison Oak Plant Dermatitis-2
Credit: DermNet NZ

The rashes may also occur in stages. "[First], the rash look like red, itchy bumps on the skin," says Dr. Jaliman. "Then it will become blistered, and then crusted." It can take up to two weeks for a poison oak rash to fully heal, as long as there's no infection, per the ASA.

While most people will only experience a red, itchy rash, a portion of the population may develop more a more serious allergic reaction (10%-15% of the US population is severely allergic to urushiol, per the ASA). According to the American Academy of Dermatology Association (AADA), if you have any of these symptoms, you are having a serious allergic reaction to poison oak and should seek immediate medical care:

  • Difficulty breathing or swallowing
  • A rash around your eyes, mouth, or on your genitals
  • Facial swelling, especially around your eyes
  • Severe itching that prevents sleep and worsens over time
  • Rashes on most of your body
  • If you develop a fever (in addition to basic poison oak symptoms)

How can you treat and prevent a poison oak rash?

If you think you've been exposed to poison oak, the first thing you want to do is wash your skin thoroughly with soap and water, says Dr. Jaliman. This helps to prevent spreading the oil to other parts of your body.

To help with itching-which you don't want to do-Dr. Jaliman also advises using cool compresses or a short, lukewarm bath with colloidal oatmeal. All of our experts also recommend using topical ointments like OTC cortisone cream or calamine lotion to reduce itching and inflammation. Anti-histamines like Benadryl can help reduce the allergic reaction, says Dr. Jaliman, while Dr. Zeichner says Vaseline can also help soothe and protect irritated areas.

In cases of severe allergic reactions, oral steroids can sometimes be prescribed, says Dr. Stevenson. And if the rash is extensive, you should see a dermatologist who can prescribe prescription strength creams or medication. "Prednisone can be taken and will get rid of this rash within a few days to a week," says Dr. Jaliman.

Prevention, however, should be your first line of defense against poison oak rashes. "Know how to identify the plant and avoid it. If you're going to be in a woody area, make sure to wear long pants and sleeves," advises Dr. Zeichner. Dr. Jaliman also recommends ivy blocker products, like Ivy X which "create a barrier on your skin, making it harder to get the rash."

In addition to protective barriers and layers, Dr. Jaliman suggests washing materials that may have encountered these plants and could bring the oils indoors, such as gardening tools and gloves, the clothes you wore during the outdoor encounter, and even your pets.

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