What is Poison Ivy? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Upon contact with human skin, poison ivy often causes a rash, known as contact dermatitis. (1) This rash may develop into increased redness, swelling, and blisters, which are often itchy or painful.

While poison ivy can grow in completely wild areas, it often thrives in places that have been disturbed by humans, such as along the sides of roads and trails, or on the edges of cleared or developed plots of land.

“It’s one of those species that are able to grow where others cannot,” says Linda Radimecky, an interpretive naturalist at Afton State Park in Hastings, Minnesota.

Some reactions to poison ivy are relatively mild and can be treated at home using over-the-counter (OTC) medicines or home remedies to relieve discomfort. But in severe cases, you should seek medical treatment.

You can take steps to prevent a poison ivy reaction by wearing protective clothing if you think you might come in contact with the plant, and by properly cleaning your clothes and skin within 30 minutes of a potential exposure.

Identifying Poison Ivy: More Than ‘Leaves of Three’

An important step in limiting your exposure to poison ivy is, of course, knowing what it looks like.

Many people are familiar with the phrase, “Leaves of three, let it be” — but according to Radimecky, this usually isn’t enough information to avoid the plant.

First, what does “leaves of three” actually mean? “The leaves each have a leaf stem,” says Radimecky. “On poison ivy, three leaf stems branch from the same spot on the plant.”

The two leaf stems on the sides, she notes, tend to be shorter than the one in the middle.

As for the color of its leaves, poison ivy can vary widely. “Sometimes they’re green, sometimes they’re red. Sometimes they’re shiny, sometimes they’re not,” Radimecky says.

Poison ivy leaves do have a defining feature: They’re not usually symmetrical. “One side of the leaf might not be the same as the other side, and the three leaves on the plant are not identical,” says Radimecky. “That’s very odd in the plant world.”

Poison ivy leaves may be toothed or lobed but may also be smooth-edged.

The plant itself usually isn’t very tall — generally less than a foot high, according to Radimecky, unless it’s climbing the side of a tree or another vertical surface. But in some areas it grows as a bushy shrub, up to four feet tall. (2)

Signs and Symptoms of Poison Ivy

A poison ivy skin rash can arise in as little as four hours if you’ve previously been exposed to the plant, or as long as three weeks if it’s your first exposure to it.

Symptoms of a skin rash may include:

  • Redness, often in streaks or lines
  • Black spots or streaks (3)
  • Intense itching
  • Blistering
  • Swelling, especially if the reaction is serious

The severity of your reaction will depend on your natural level of sensitivity, as well as how much of the plant’s oil has bonded to your skin.

Getting more of the oil on your skin may also cause a rash to develop sooner.

If you inhale smoke containing the oil from poison ivy, symptoms may include irritation in your airway and lungs and difficulty breathing.

Causes and Risk Factors of Poison Ivy

Poison ivy contains an oily resin known as urushiol. It’s found in the leaves, stems, and roots of the plant, and it’s both colorless and odorless.

This oily substance easily sticks to many different types of surfaces when it comes into contact with them, including skin, clothing, pet fur, and outdoor tools and equipment.

If the oil comes into contact with an object and isn’t washed off afterward, it’s possible to have a skin reaction after touching that object — even years later. (4)

“If you get it on your shoelace, then you tie your shoe and you wipe your forehead, you could have poison ivy on your forehead,” Radimecky says.

10 Myths About Allergies

When the oil from poison ivy touches your skin, it bonds to the area and causes a reaction from your body’s own immune system. This reaction is known as allergic contact dermatitis.

Most people are susceptible to this allergic reaction from poison ivy, but about 15 percent of people won’t ever get a reaction, according to the American Skin Association. (1)

No one is born allergic to poison ivy, though.

“Our bodies become sensitized to poison ivy after an initial exposure,” says Joshua Zeichner, MD, the director of cosmetic and clinical research in dermatology at Mount Sinai Hospital in New York City. “Upon future exposure, our immune system becomes activated, leading to significant inflammation.”

In addition to direct contact and touching contaminated items, you can also have a poison ivy reaction by breathing smoke from the plant if it's burned. This can harm your nasal passages and lungs, and can cause a severe reaction in some people.

Poison ivy isn’t contagious unless there is still oil from the plant on your skin and you spread it to other surfaces. You also can’t spread a rash across your body by scratching once you've washed off the oil.

If a skin rash appears to spread, it’s probably because the area was already exposed and it's experiencing a delayed reaction. Or you may have oil from the plant under your fingernails, or you've unknowingly touched a contaminated item.

How Is Poison Ivy Diagnosed?

Poison ivy is diagnosed on the basis of symptoms — itching, redness, and bumps, blisters, or streaks on the skin. Knowing where someone was, what they were doing, and what they may have touched during the hours before the symptoms appeared can make diagnosis easier.

Duration of Poison Ivy

A skin rash from poison ivy typically lasts one to three weeks, according to the American Academy of Family Physicians. (5)

After about a week, your blisters will start to dry up, and the rash should begin to fade.

More severe skin reactions, or those covering larger areas of your body, may take longer to clear up.

Your skin rash may also last longer if it’s your first reaction to poison ivy — for as long as three to four weeks. (6)

Treatment and Medication Options for Poison Ivy

Most of the time, treatment for poison ivy consists of self-care to alleviate discomfort.

The most important first step in treating any reaction, according to Dr. Zeichner, is to make sure none of the plant’s oil remains on your skin.

If you haven’t already, he says, wash the area immediately with a gentle cleanser, and also make sure that any exposed clothing gets washed thoroughly.

Once you’re sure you’ve removed any remaining plant oil, try the following steps to help soothe your rash:

  • Take an anti-inflammatory pain reliever, such as Advil or Motrin (ibuprofen) or Aleve (naproxen).
  • Take an oral antihistamine, such as Benadryl (diphenhydramine).
  • Apply an over-the-counter steroid cream (such as hydrocortisone) for the first few days.
  • Apply calamine lotion, which can reduce itching.
  • Apply a heavy-duty moisturizer, such as one containing petrolatum.
  • Soak the affected area in a cool or lukewarm bath containing oatmeal or baking soda.
  • Place a cool, wet compress on the area for 15 to 30 minutes several times each day.
When to See a Doctor for Poison Ivy

It’s usually not necessary to see a doctor for a poison ivy rash. Most rashes will clear up by themselves in a couple of weeks.

But if your reaction is serious or widespread, you’ll need to seek treatment to help alleviate your discomfort and limit the risk of serious complications.

The following situations in a poison ivy reaction require medical attention:

  • A fever over 100 degrees F (37.8 degrees C)
  • Pus or yellow scabs on your rash
  • Tenderness or itching that gets worse or disturbs sleep
  • A rash that covers your eyes, mouth, or genital area
  • A rash that covers large areas of your body
  • A large area of broken blisters, or other broken skin
  • No sign of improvement after a few weeks
  • Difficulty breathing

Prevention of Poison Ivy

There’s a lot you can do to prevent a poison ivy reaction in the first place — both by reducing your risk of exposure and by acting quickly if you know you’ve been exposed.

Avoid areas where poison ivy thrives. If you’re hiking or camping, stay on designated trails or campsites and away from areas where you know poison ivy plants have returned after being cleared.

Remove poison ivy from your property. In your own yard, you can get rid of poison ivy either by applying an herbicide or by pulling it out of the ground.

If you decide to pull the plant out, be sure to wear heavy gloves and to remove the roots along with the plant. Afterward, carefully remove the gloves and wash them and your hands thoroughly.

Never burn poison ivy that you’ve removed, because the smoke will contain the plant’s toxic oil. Seal it in a heavy-duty garbage bag and place in the trash.

Wear protective clothing. Sometimes it’s not possible to avoid areas prone to poison ivy growth — especially if you work in landscaping or gardening, construction, farming, or cable installation.

Depending on your activity, it can help to wear long pants tucked into boots, as well as long sleeves tucked into protective gloves.

Wash clothing and objects after potential contact. Be sure to remove your clothing carefully — without letting it touch furniture, rugs, or appliances — and wash it promptly in a washing machine. Wash boots and shoes using detergent and water.

It’s also a good idea to wash items like gardening tools and recreational gear. Remember to wear long dishwashing gloves while washing or handling any potentially exposed item.

Wash your skin after known or potential contact. Even if your skin touches poison ivy, you can still prevent or limit an allergic reaction by cleaning it with soap and water as quickly as possible.

According to the Mayo Clinic, there’s a good chance you’ll prevent a rash if you wash your skin within 30 minutes of exposure. Even after an hour, you can limit the severity or any reaction by washing.

Teach your family and friends to recognize the plant. Once you’ve educated yourself about poison ivy, educate your family and friends. That way you can all look out for each other when spending time outdoors.

Mind your pets. Even though most pets don’t get a reaction from poison ivy, they can spread its oil to humans.

Try not to let your pet wander into areas where poison ivy may grow. If you think your pet may have been exposed, give the animal a bath using an appropriate shampoo while wearing rubber or vinyl gloves.

There’s one animal that you may want to set loose in areas with poison ivy: goats. Not only are they not allergic to the plant, but goats will help clear poison ivy from certain areas by eating it. (7)

Complications of Poison Ivy

Serious complications from a poison ivy reaction are rare.

The most troublesome problem to look out for is swelling, especially if your face swells or your eyes swell shut. This can result in lasting or serious damage.

It’s also possible for a poison ivy rash to get infected, especially if you scratch the area and break open blisters. Bacteria under your fingernails are often the source of this infection, which may need to be treated with antibiotics.

Usually, the only lasting effects of a poison ivy reaction are cosmetic — and even these tend to fade away eventually.

“Extremely severe cases theoretically can lead to scarring,” says Zeichner. But more commonly, he says, a rash will leave behind a red or brown stain.

This stain tends to diminish and eventually disappear over a number of weeks, and it isn’t a reason for medical concern.

Research and Statistics: How Many People Have Poison Ivy?

As many as 50 million Americans have a poison ivy reaction each year, making it the most common allergy in the United States, according to the American Skin Association. (1)

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