What is Black Spot Poison Ivy?

Patient Presentation
A 16-year-old female came to clinic with linear black streaks on her arms that began the day before. She had been in the woods and fields in the morning and in the afternoon noticed the black streaks. During the night she awoke because of intense itching and noticed that she now also had reddened skin with vesicles in the area around the black streaks. She denied direct exposure to any poison ivy, poison oak, etc., and said that after being in the woods she had washed her clothing and showered. She had had poison ivy in the past and thought this looked similar but it had never been black before. The pertinent physical exam showed a healthy female with normal growth parameters and vital signs. Both volar forearms and right dorsal forearm had linear black lines that were 1-3 cm in length and ~2-3 mm wide. There were 2-3 black lines in each location. Surrounding the areas were linear reddened skin with some shiny vesicles and scratch marks. The rest of her examination was negative.

The diagnosis of of black spot poison ivy was made. “This doesn’t happen very much, but you got a pretty good exposure to some poison ivy and this is why it is black. We treat it the same though. I recommend that you use some antihistamines and I’ll prescribe a steroid cream. I know you said you washed all the clothing but make sure that you wash anything else you might have contacted like garden gloves, backpack etc. because the resin can stay on those too for a long time,” the physician said.

Poison ivy (PI, Toxicodendron radicans) is a common plant in North America that causes allergic contact dermatitis. Poison oak and sumac also cause similar problems. The rash usually appears as linear erythematous papules or vesicles occurring soon after exposure.

Patients often do not identify the exposure specifically but will say they were walking/playing in gardens, fields or woods. PI can be a small plant, vine or even a shrub. The coloring changes over the growing season. Fires may also be a source as burning the plants and being in the smoke can cause extensive lesions on the body. The plant has 3 leaves and never more. The leaf stems alternate along the growing plant and are not found directly across from each other. The leaves have smooth edges and are not saw-toothed, serrated or scalloped. There also are no thorns. Several identification guides can be found here.

PI has an oleoresin called urushiol which causes the main problem but it also contains allergens (pentadecylcatechols). The urushiol does not evaporate well and therefore stays on clothing, sports equipment etc.. for longer time periods. The allergens can contaminate clothing for years. These properties account for exposure at unexpected times of the year (i.e. in the winter children using a contaminated sleeping bag for an overnight party and getting the PI rash), or in unexpected places (e.g. PI rash presenting in the United Kingdom which has no PI after travel to the United States).

Treatment is by antihistamines and topical or oral steroids, along with appropriate skin hygiene. Oral steroids for extensive lesions usually need to be tapered over a long time to prevent rebound symptoms. Prevention is by avoiding exposure. Use of protective clothing including areas between garments such as socks over pant legs, long-cuffed gloves that cover sleeves, and hoods or handkerchiefs to protect the neck can decrease exposure. As soon as possible, the person and all clothing and equipment should washed thoroughly to prevent the rash and further contamination of other clothing/equipment. Washing with soap and not just plain water increases prevention efficacy. Fresh jewelweed plant mash (Impatiens capensis) has been shown to decrease PI rash after exposure but not its extract or that which is added to soap. Although the author does not have scientific evidence to support the practice, the author personally recommends rubbing soap on potentially exposed areas such as wrists, ankles, neck etc.. before potential exposure and then showering immediately after exposure. In her experience, it is a low-cost, reasonably effective preventative measure.

PI plant is part of a larger family called Anacardiacaea which is a flowering, sap producing family. Mangos, cashews and pistachios are examples of this family. Other species are used for tanning and lacquers. There is global experience where first exposure to urushiol orally appears to induce tolerance to the resin and people do not react to it when it is encountered dermally; that is, they have an induced oral tolerance for the resin. People who eat mangos from an early age, children who eat chicken off of lacquerware that contains the resin (i.e. “lacquer chicken” in Korea) or Native American orally ingesting the plant are all examples of groups of people who seem to have tolerance after dermal exposure to the resin.

Learning Point
Black spot PI is an atypical variation where the initial lesions are spots or linear black streaks that are followed by the more classic presentation several hours later. The black coloring is because of high concentrations of the urushiol which oxidizes in a warm, humid environment. The black lesions cannot be washed off but they will peel away with time and do not scar. It is treated the same as regular PI.

Questions for Further Discussion
1. What PI or similar plants are in your location?
2. What skin hygiene measures do you recommend for PI?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Poison Ivy, Oak and Sumac

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Poison Ivy. Available from the Internet at http://www.poison-ivy.org. (cited 11/29/16).

Anacardiacaea. Wikipedia. Available from the Internet at https://en.wikipedia.org/wiki/Anacardiaceae. (cited 11/29/16).

Abrams Motz V, Bowers CP, Mull Young L, Kinder DH. The effectiveness of jewelweed, Impatiens capensis, the related cultivar I. balsamina and the component, lawsone in preventing post poison ivy exposure contact dermatitis. J Ethnopharmacol. 2012 Aug 30;143(1):314-8.

Pittman MA, Lane DR. Black spot poison ivy: under the cover of darkness. J Emerg Med. 2013 Apr;44(4):e331-2.

Colbeck C, Clayton TH, Goenka A. Poison ivy dermatitis. Arch Dis Child. 2013 Dec;98(12):1022.

Sinha K, Elpern DJ. A baleful weed and the king of fruits: tolerance, immunity, and the microbiome. Int J Dermatol. 2016 Jan;55(1):121-2.

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa Children’s Hospital