Poison ivy, poison oak, and poison sumac are plants that can cause an allergic skin reaction. These poisonous plants contain an oil that can trigger the body’s immune system and produce a rash. Becoming familiar with the appearance of these plants can help a person identify and prevent an allergic rash from exposure.

The Centers for Disease Control and Prevention (CDC) note that while the expression “leaves of three, let it be” can be helpful for identifying poison ivy and poison oak, this is not true for poison sumac, as this plant usually has clusters of 7–13 leaves. Additionally, some species of poison ivy and oak may also have more than 3 leaves.

If a person suspects contact with one of these plants, the CDC recommends they wash the exposed skin and scrub their nails. When a rash appears, applying wet compresses or hydrocortisone cream can help reduce itching and blistering. However, if the rash is severe or if someone is having trouble breathing, they should get immediate medical attention.

In this article, we discuss how a person can identify poison oak, poison ivy, and poison sumac, as well as symptoms, treatment, and prevention of the rash.

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Toxicodendron is a group, or genus, of woody plants belonging to the Anacardiaceae family. The name derives from the Greek words for “toxic tree.” The Toxicodendron genus includes a number of plants known for their toxicity that grow throughout the United States.

The key to avoiding exposure to poison oak, ivy, and sumac is being able to recognize them. The U.S. Food and Drug Administration (FDA) provides the below information on how to identify the plants:

Poison oak

Poison oak grows in long vines or tall clumps on the Pacific Coast. It is also present in the southern and eastern United States as a low shrub. The plant has fuzzy green leaves, usually in groupings of three. The leaves of poison oak are typically either deeply toothed or lobed with rounded tips. Yellow-white berries may be present.

Poison ivy

Poison ivy grows throughout the 48 contiguous states except for parts of the West Coast. It grows as a small shrub or vine trailing along the ground. The plant may also grow on low plants, poles, and trees.

Every leaf has three glossy leaflets that have toothed or smooth edges. The leaves are green in summer, reddish in the spring, and red, orange, or yellow in the fall. Whitish-yellow berries and greenish-white flowers may be present.

Poison sumac

Poison sumac grows as a small tree or tall shrub in swamps or bogs in the Midwest, Northeast, and parts of the Southeast. The leaves consist of clusters of 7–13 leaflets with smooth edges, which are green in summer, orange in the spring, and red, orange, or yellow in the fall. Yellow-greenish flowers and clusters of whitish-green berries may be present.

When poison oak, ivy, and sumac are damaged, bruised, or burned, they release an oil called urushiol. If it gets on a peson’s skin, most people experience an allergic reaction that manifests as an itchy, red rash with blisters or bumps. Exposure to just 50 micrograms, which is less than one grain of table salt, can trigger a rash in 80–90% of adults.

Exposure may result from:

  • direct contact through handling or brushing against the plant
  • indirect contact through touching tools, clothing, or animals such as household pets that have urushiol on them
  • inhalation of urushiol from burning plants, which can cause lung irritation

Following exposure, the time it takes for a rash to appear depends on whether a person has had a prior rash from poison ivy, oak, or sumac. Typically, if an individual has not had a previous rash from the plants, the rash usually appears within 2–3 weeks. In someone who has experienced a previous rash from the plants, the rash may manifest within 4–48 hours.

Symptoms may include:

  • red rash
  • itching
  • swelling
  • possible streaking, patches, bumps, and weeping blisters

Most people who get the rash experience the following course:

  • The first symptom is intense itching where the rash will appear.
  • Shortly after itching starts, the rash develops.
  • Next, if a person has blisters, they break open and leak fluid.
  • Lastly, the blisters form a crust, and the rash disappears in 2–3 weeks, even without treatment.

The CDC recommend these measures if a person is exposed to poison ivy, oak or sumac:

  • Immediately rinse the skin with rubbing alcohol, dishwashing liquid, detergent, or a specialized poison plant wash and plenty of water.
  • Rinse frequently to prevent the wash solution from drying the skin and spreading exposure to the urushiol.
  • Clean under the nails with a brush.

If a rash appears, take the following steps:

  • Apply calamine lotion, wet compresses, or hydrocortisone cream to the exposed skin to decrease blistering and itching. Follow the directions on the package when applying a cream, but do not apply to broken skin.
  • Take an oatmeal bath, as it may relieve itching.
  • For further itching relief, take an antihistamine such as diphenhydramine (Benadryl). Use it according to the package directions. If a child has come into contact with a poison plant, it is advisable to ask a pediatrician about dosage. Note that Benadryl can cause drowsiness.

A person can do several things to try and prevent a rash. The FDA advises the below practices:

  • Learn what the plants look like to be able to avoid them. Watching online videos can help someone become familiar with their appearance.
  • Wear long sleeves, long pants, and gloves when working in the garden to protect the skin from exposure.
  • Wash the skin as soon as possible after exposure. Do not delay because this can help prevent further spread of any reaction.
  • Wash an exposed pet with pet shampoo and water while wearing rubber gloves. Although pets are not sensitive to poison plants, petting them can expose someone to the oil on the fur and produce a reaction.
  • To avoid inhalation of the urushiol, do not burn plants that may be poisonous.

The FDA recommends seeing a doctor if:

  • an individual has a fever higher than 100°F (38°C)
  • the rash covers more than one-fourth of the skin
  • there is tenderness, pus, or soft, yellow scabs on the rash
  • the rash does not improve within a few weeks

Sometimes a person may need more urgent care. The CDC advise immediate medical attention if the rash is severe or if it is on the face or genitals.

If a person has a severe allergic reaction, such as difficulty breathing or swelling, or if they have had a severe allergic reaction in the past, they require immediate help. Call 911 or take them to a hospital emergency room.

Toxicodendron plants, such as poison oak, ivy, and sumac are poisonous plants that can secrete a toxic oil called urushiol. Learning to identify these plants and being able to differentiate them from similar plants is the most important way to prevent exposure. It is also important to remember that exposure can be indirect, such as touching garden tools and pets that have had contact with the plants, or from inhaling smoke from burning plants.

Following contact, a rash may appear within a few hours to 2–3 weeks. The rash will typically go away without treatment, but medications, such as hydrocortisone cream, calamine lotion, and antihistamine tablets, can relieve itching and make a person feel more comfortable.

If a person has an extreme reaction to these plants, it is advisable they receive immediate medical attention if an exposure occurs.