“Leaves of 3, Let Them Be”--Poison Ivy, Oak and Sumac by Mark B. Levin, M.D., Timothy J. Patrick-Miller, M.D. and Louis J. Tesoro, M.D. The Pediatric Group, P.A., Princeton

This is the seventh article in a series written for Princeton Online on summer hazards. Click here for an archive of other articles.

The common dictum cited above describing plants with 3 leaves originating from the same point on the plant is accurate only for Rhus radicans (poison ivy) and Rhus toxicodendron (poison oak). Rhus vernix (poison sumac), which typically grows in swampy areas, has clusters of 7 to 13 leaves. The reaction to direct (leaves, stem, root or woody vine) or indirect (clothing, shoes, tools and animal fur) contact can occur in 1 to 2 days for those who are very sensitive to the plant oil (urushiol) or as late as 9 to 14 days for those who are not very sensitive and have never before been exposed.

The rash begins as itchiness and usually progresses through stages of redness, swelling and papules (bumps). More severe cases can blister. The irregular pattern that Rhus dermatitis causes on the skin is called “scratch mark distribution” because the oil is spread wherever it has been put by the hands (including around the eyes and the ano-genital area). The folklore that poison ivy travels around the body or from person to person after it appears is not true. Once the skin has been washed and the nails have been cleaned, the offending oil is removed. Increased skin sensitivity in certain body parts or greater amounts of the oil can cause different rates of rash appearance, giving the impression that the rash is traveling. Blisters contain a person’s own body fluid--not the plant oil. This fluid can not spread the rash.

Treatment involves topical symptomatic relief with products such as cortisone cream, Rhulli gel®, Itch-X®, Aveeno Cream® or Clear Caladryl®. Preparations that contain diphenhydramine (Benadryl®) should not be applied to broken skin. For weepy lesions, compresses of Domeboro® solution aid drying. Oral antihistamines, such as hydroxyzine (Atarax® or Vistaril®), diphenhydramine (Benadryl®), cyproheptadine (Periactin®), loratidine (Claritin®)or cetirizine (Zyrtec®) can be helpful in controlling itching. Oral steroids are reserved for more severe cases, especially if the eyelids are swollen shut or the genitalia are involved. Avoidance of injury to the skin from scratching, repeat exposure to the plant oil or exposure to the sun is advisable. Healing takes 4 to 14 days, depending on the extent and severity of the rash.

Allergy shots for Rhus dermatitis were popular several decades ago. Unfortunately, they have not been shown to be effective. Most physicians have abandoned their use. The mainstay in preventative management is recognizing the plants and avoiding contact with them. Many people do not realize that the hairy projections on the woody vines that climb many trees are poison ivy plants. Also, when removing contaminated clothing or gloves, be sure not to touch the outside of the garment with your skin and launder them immediately. Ivy Block®, a topical pre-exposure preventative has not been shown to be reliably effective.

Although other plants may cause dermatitis if a particular person is sensitive to them, none are as universally feared (or celebrated, as in the song, “Poison Ivy”) as the Rhus family. The treatment is the same for other plant induced dermatidites. Some very sensitive people may have a Rhus-like dermatitis from the skin of the Mango, which contains a similar oil.

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Dr. Levin has been a member of the staff at The Pediatric Group since 1977. Currently an attending Pediatrician at the Medical Center at Princeton, he has been Chairman, Department of Pediatrics, Medical Center at Princeton, 1984 to 1986, 1989 to 1992, and past President, Medical and Dental Staff, Medical Center at Princeton, 1987 to 1988. Dr. Levin has served on numerous Departmental and hospital committees. He has published original articles both while at Upstate Medical Center in Syracuse and at The Pediatric Group. He has a wife and three children. Dr. Levin enjoys alpine skiing, jogging, hiking and camping, travel, computers and racquetball.

Dr. Patrick-Miller has been a member of the staff at The Pediatric Group since 1985. Dr. Patrick-Miller has served on several Departmental and hospital committees. He has published original work while at The Pediatric Group. He and his wife enjoy travel. He also likes hiking, biking, gardening and reading.

Dr. Tesoro has been a member of the staff at The Pediatric Group since 1988. Dr. Tesoro is Chairman, Department of Pediatrics, Medical Center at Princeton, 1996 to present and Attending Pediatrician, Medical Center at Princeton, 1988 to present. He has served on several Departmental and hospital committees, lectured at the Universiy of Pennsylvania and has published original articles both while at The Children's Hospital of Philadelphia and at The Pediatric Group.