Identifying Poison Ivy With Detection Patches

Toxic Urushiol Oil Is Found in Poison Ivy, Poison Oak, and Poison Sumac

Poison Ivy
  Cyndi Monaghan / Getty Images

Experienced outdoors enthusiasts usually have a good idea what poison ivy looks like, but many people have trouble identifying it at certain times of the year or when poison ivy (Rhus radicans) is mixed in with other dense ground cover plants. Identification is pretty important, though, as you know if you have ever experienced the itchy, painful rash that comes with exposure to urushiol, the toxic oil in poison ivy that it causes the rash. Some 50 million Americans develop a poison ivy rash each year, according to the American Skin Association, and for some people who are especially allergic to urushiol, it can lead to weeks or even months of misery.

Having a good familiarity with what poison ivy looks like in different seasons is still a good idea for anyone who regularly spends time in the woods or doing yard work, but several different "detection cloth" products are also available. These products help you identify the plant by crushing a leaf in a specially treated patch of cloth and watching for a chemical reaction. The most familiar brand of detection patch is sold under the name See Leaf. The patches can be used to test for poison ivy, as well as poison oak and poison sumac, plants which also contain urushiol and can cause painful, itchy rashes.

Using Poison Ivy Detection Patches

The See Leaf product comes in a light-sealed pouch containing 10 small cloths. The pouch can easily be slipped into a pocket. To use a patch, simply remove it from its envelope and use it to crush a small leaf of the suspected plant, pinching the leaf inside the cloth and rubbing thumb and finger together. The manufacturer strongly suggests wearing a glove while crushing the leaf.

If the leaf contains urushiol, the chemical in the cloth will react with it, turning bright pink. If you don't see pink, you are safe—the plant is not poison ivy.

To test for poison oak or poison sumac, the process is slightly different. Cut a small nick out of a branch or stem of the suspected plant, wait for the sap to ooze up in the wound, the rub the sensing patch against the wound to absorb some of the sap. Once again, if there is urushiol present, the cloth will turn bright pink, identifying the plant as poison oak or poison sumac.

The cloth should be throw away after use, and make sure to thoroughly wash the gloves or knife you used to take the sample. If you have come into contact with the plants, now is the time to thoroughly wash all skin and to launder clothing, since you likely have time to remove the urushiol oils before they cause a skin reaction.

How Reliable Is a Detection Patch?

The key to good identification with this patch product is to make sure the leaf is vigorously crushed to fully release the urushiol oils. Merely touching the cloth the leaf or stem will not initiate the color change. If you are testing the stems of suspected poison oak or poison sumac, it is important to make sure you are testing actively oozing sap—merely touching dry wood will not cause the patch to react.

But if you follow manufacturers instructions, the See Leaf detection patches have a very good rate of accuracy for all plants containing urushiol, including poison ivy, poison oak, and poison sumac. Although less well known, cashew and mango trees also contain urushiol and can cause reactions in sensitive individuals.


Good visual familiarity with poison ivy remains the best preventive measure. Learn what poison ivy looks like in various seasons and in all its forms, and be on the lookout for suspicious vines along the ground or growing up trees and shrubs when you are in the woods or working in brushy margins along your property. If you suspect poison ivy, use See Leaf patches to verify. Time is fairly important here, since removing the urushiol oils quickly can prevent the tell-tale rash from developing. Soap and water applied in copious amounts will help remove most of the urushiol oils, but there are also specially formulated skin wash products that can neutralize the oils. If you manage to remove all oils within 8 hours of exposure, there is a good chance you will avoid the skin rash altogether.

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