Poison Ivy...Outsmarting Poison Ivy and Its Cousins

What is poison ivy, poison oak, and poison sumac?

The Summer is upon us and so are those nasty rashes from brushing up against poisonous plants such as poison ivy, poison oak, and sumac.  Approximately 85 percent of the population will develop an allergic reaction if exposed to poison ivy, oak or sumac, according to the American Academy of Dermatology.

Poison Ivy, Poison Oak, Poison Sumac

Usually, people develop a sensitivity to poison ivy, oak or sumac only after several encounters with the plants, sometimes over many years. However, sensitivity may occur after only one exposure.

The cause of the rash, blisters, and infamous itch is urushiol (pronounced oo-roo-shee-ohl), a chemical in the sap of poison ivy, oak and sumac plants. Because urushiol is inside the plant, brushing against an intact plant will not cause a reaction. But undamaged plants are rare.

Poison oak, ivy and sumac are very fragile plants, and stems or leaves broken by the wind or animals, and even the tiny holes made by chewing insects, can release urushiol.

Reactions, treatments and preventive measures are the same for all three poison plants. Avoiding direct contact with the plants reduces the risk but doesn't guarantee against a reaction. Urushiol can stick to pets, garden tools, balls, or anything it comes in contact with. If the urushiol isn't washed off those objects or animals, just touching them--for example, picking up a ball or petting a dog--could cause a reaction in a susceptible person. (Animals, except for a few higher primates, are not sensitive to urushiol.)

Urushiol that's rubbed off the plants onto other things can remain potent for years, depending on the environment. If the contaminated object is in a dry environment, the potency of the urushiol can last for decades, says Epstein. Even if the environment is warm and moist, the urushiol could still cause a reaction a year later.

Almost all parts of the body are vulnerable to the sticky urushiol, producing the characteristic linear (in a line) rash. Because the urushiol must penetrate the skin to cause a reaction, places where the skin is thick, such as the soles of the feet and the palms of the hands, are less sensitive to the sap than areas where the skin is thinner. The severity of the reaction may also depend on how big a dose of urushiol the person got.

What can you do to avoid poison ivy, poison oak, and poison sumac?

Learn what poison ivy looks like and avoid it. While "leaves of three, beware of me, is the old saying, "leaflets of three, beware of me" is even better because each leaf has three smaller leaflets.

Wash garden tools regularly, especially if there is the slightest chance that they've come into contact with poison ivy. If you know you will be working around poison ivy, wear long pants, long sleeves, boots, and gloves.

Hikers, emergency workers, and others who have a difficult time avoiding poison ivy may benefit from a product called Ivy Block, made by EnviroDerm Pharmaceuticals Inc.. It's the only FDA-approved product for preventing rashes from poison ivy, oak, or sumac. The OTC lotion contains bentoquatam, a substance that forms a clay-like coating on the skin.

If you come into contact with poison ivy, oak, or sumac, wash the skin in cool water as soon as possible to prevent the spread of urishiol. If you get a rash, oatmeal baths and calamine lotion can dry up blisters and bring relief from itching. You can also talk to a health care professional about medicines that may help.

How can you deal with the rash?

If you don't cleanse quickly enough, or your skin is so sensitive that cleansing didn't help, redness and swelling will appear in about 12 to 48 hours. Blisters and itching will follow. For those rare people who react after their very first exposure, the rash appears after seven to 10 days.

Because they don't contain urushiol, the oozing blisters are not contagious nor can the fluid cause further spread on the affected person's body. Nevertheless, Epstein advises against scratching the blisters because fingernails may carry germs that could cause an infection.

The rash will only occur where urushiol has touched the skin; it doesn't spread throughout the body. However, the rash may seem to spread if it appears over time instead of all at once. This is either because the urushiol is absorbed at different rates in different parts of the body or because of repeated exposure to contaminated objects or urushiol trapped under the fingernails.

The rash, blisters and itch normally disappear in 14 to 20 days without any treatment. But few can handle the itch without some relief. For mild cases, wet compresses or soaking in cool water may be effective. Oral antihistamines can also relieve itching.

There are a number of OTC products to help dry up the oozing blisters, including:

  • aluminum acetate (Burrows solution)
  • baking soda
  • Aveeno (oatmeal bath)
  • aluminum hydroxide gel
  • calamine
  • kaolin
  • zinc acetate
  • zinc carbonate
  • zinc oxide

How to identify poison ivy, poison oak, and poison sumac

Unfortunately, poison ivy, oak and sumac don't grow with little picture ID badges around their stems, so you have to know what to look for. To avoid these plants and their itchy consequences, here's what to look for.

Poison Ivy

  • grows around lakes and streams in the Midwest and the East
  • woody, ropelike vine, a trailing shrub on the ground, or a free-standing shrub
  • normally three leaflets (groups of leaves all on the same small stem coming off the larger main stem), but may vary from groups of three to nine
  • leaves are green in the summer and red in the fall
  • yellow or green flowers and white berries

Poison Oak

  • eastern (from New Jersey to Texas) grows as a low shrub; western (along the Pacific coast) grows to 6-foot-tall clumps or vines up to 30 feet long
  • oak-like leaves, usually in clusters of three
  • clusters of yellow berries

Poison Sumac

  • grows in boggy areas, especially in the Southeast
  • rangy shrub up to 15 feet tall
  • seven to 13 smooth-edged leaflets
  • glossy pale yellow or cream-colored berries

Source: Food and Drug Administration

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Last Editorial Review: 7/18/2006

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