How to Prevent and Treat Poison Ivy

Poison ivy, also known as Rhus dermatitis, is a type of skin rash caused by contact with the resin of plants in the Anacardiaceae family and Rhus genus (sometimes classed in the genus Toxicodendron). These plants include poison ivy, poison oak, and poison sumac.

The resin, called urushiol, can also be found in the cashew tree, mango tree, Japanese lacquer tree, and the marking nut tree. Ginkgo biloba contains a similar substance that can cause dermatitis in people who are sensitive to urushiol.

In the United States, poison ivy, poison oak, and poison sumac are among the most common causes of contact dermatitis. Millions of Americans require medical attention each year after being exposed to one of these plants.

Poison Ivy (Toxicodendron radicans)
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How to Identify a Suspect Plant

The three main types of plants that cause Rhus dermatitis vary in both their appearance and geographic location.

  • Poison ivy leaves are most often notched on the edges and arranged in groups of three (although some varieties are smooth-edged). Poison ivy is usually found east of the Rocky Mountains as either vines or shrubs.
  • Poison oak leaves grow in groups of either three, five, or seven. The leaves are smaller than poison ivy and have smooth, rounded edges. Poison oak is usually found west of the Rocky Mountains as a small bushy plant or climbing vine.
  • Poison sumac has seven to thirteen leaves on one stem pointing at an upward angle. They are oval, smooth-edged, and about 10 centimeters long. Poison sumac is found in boggy areas of the South.

How Poison Ivy Develops

Poison ivy occurs when a person comes into contact with the leaf and/or internal parts of the stem or root. The rash typically develops within 24 to 48 hours of exposure, though it can develop sooner. It usually appears in a linear or circular pattern with itchy red blotches. Rhus dermatitis is incredibly itchy, to the point that the victim may scratch the skin to the point of bleeding.

The resin itself can be active for years following exposure (meaning that it can be spread to others who come into contact with the clothing of an affected individual). By contrast, the fluid from the blisters cannot spread the rash.

If untreated, the rash usually heals in around three weeks.

Treatment of Poison Ivy

Poison ivy mostly occurs on exposed areas on the arms, legs, and face. The intensity of the rash can vary based on the person's sensitivity to the resin, as well as the amount and/or extent of exposure.

There are several ways to treat the rash:

  • Wash the skin with soap and water to inactivate and remove the resin. Washing is most effective if it is done within 15 minutes of exposure.
  • Cold, wet compresses are effective in the early stages. They should be applied for 15 to 30 minutes several times a day for the first three days.
  • Steroid creams or ointments can be helpful in reducing the inflammation and itching. Hydrocortisone can be used on the face; a stronger, prescription-strength steroid may be needed for the arms or legs.
  • Oral steroids may be required for severe cases and must be taken for at least a week.
  • Short, cool tub baths with colloidal oatmeal can be soothing and can help control inflammation.
  • Calamine lotion can help control itching, although excessive use can dry the skin and cause even more inflammation.
  • Antihistamines such as diphenhydramine (Benadryl) that are sedating may help encourage sleep, but won't generally help itching. This is because the source of the itching in Rhus dermatitis is not primarily caused by histamine, but by white blood cell (lymphocytes) infiltration into the skin.
  • Any exposure to the eyes or eyelids, or the development of a honey-colored crust, should be evaluated by a doctor.

Tips for Preventing Poison Ivy

Clearly, the best way to avoid poison ivy, poison oak, or poison sumac is to know what the plants look like and to steer well of them. Beyond that, there are a few handy tips you should remember if you live in an area where the plants are endemic:

  • Clothing serves as the most effective barrier. Wear pants, socks, and boots if plants are known to grow in areas of heavy brush. If contact occurs, removed your clothes carefully and launder immediately.
  • Use vinyl gloves when pulling weeds. Urushiol can penetrate rubber gloves.
  • A lotion containing 5% quaternium-18 bentonite (IvyBlock) can be applied to the skin and provide protection for up to eight hours. It must be washed off before reapplying.
  • Despite popular beliefs, you cannot desensitize yourself to poison ivy by chewing leaves or being injected with commercially prepared extracts.
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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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