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In North America there is a high incidence of exposure to poison ivy/oak and sumac (PIOS) plants at residential, occupational, or recreational settings. It is estimated that 10-50 million Americans seek medical treatment annually for allergic contact dermatitis (ACD). This is not surprising since it is estimated that 50 to 75% of the U.S. population are sensitized to PIOS. Toxic plant exposure can result in discomfort, disability, lost work days, and workman’s compensation claims. Recommendations for prevention and treatment for this type of ACD has not changed significantly for many decades. Consequently, myths, and confusion about these toxic plants still remains. Thus, our aim is to focus on up-to-date prevention and treatment recommendations for mild to severe ACD.

Distribution

PIOS plants are members of the Anacardiaceae family in the genus Toxicodendron (toxico=poison and dendron=tree. Their distribution is actually very widespread and many States have all three toxic plants (See Figure 1). In North America there are five Toxicodendron species: Atlantic/Eastern Poison Ivy; Western/Northern Poison Ivy; Atlantic/Eastern Poison Oak; Pacific/Western Poison Oak; and Poison Sumac

Figure 1. Distribution of these three Toxicodendron plants in the U.S. (Figure credit: Zanfel Laboratory, Inc.)

Urushiol and Immunochemistry 

Exposure to the oil of these toxic plants, urushiol (oo-roo-shee-awl) oil, causes an allergic reaction. Urushiol is a nonvolatile oil that resides in the leaves, berries, stem, and roots of all Toxicodendron. Typically urushiol is released from damaged PIOS plants and can unknowingly get on a person’s skin, clothes, or a pet’s fur resulting in primary or secondary exposure. The binding and penetrating of urushiol on the skin causes a T lymphocyte-mediated delayed hypersensitivity reaction. This is not a histamine reaction, and the use of antihistamine oral/topical provides no symptomatic relief. It is beyond the scope of this article to discuss urushiol immunochemistry, and it is uniquely presented in this animated video.

Clinical Features

In the U.S., PIOS account for the greatest amount of ACD cases, specifically known as Toxicodendron dermatitis (TD). A typical sensitive individual presents with skin lesions in approximately 24 to 48 hours after contact with a PIOS plant (9 to 14 days in less sensitive). Extremely sensitive individuals can present with TD in 4 to 5 hours. Mild cases present with small isolated areas (10-15% of total skin area), erythema (redness), pruritus (itching), papules (raised skin), but no vesicles (small blisters) or bullae (large blisters); Moderate cases present with intense itching, redness, raised skin, and plaques with small blisters (less than 25% of total skin area); Severe cases present with extreme discomfort, redness, raised skin, severe itching, pain, and large fluid-filled blisters (25% or greater total skin area) that is followed by weeping and oozing lesions. Classically, TD is initially arranged in small isolated spots, linear streaks or large areas of red, elevated skin lesions. See Figure 2 for a spectrum of clinical images for mild to severe TD. 

Figure 2. Three examples of mild to severe allergic contact dermatitis from urushiol exposure.

Furthermore, some individuals may present with “black spot” dermatitis, which is oxidized urushiol dried on the skin. Urushiol can be aerosolized during forest fires and carried in smoke particles. Wildland firefighters (or others who are exposed and sensitive) can develop respiratory tract inflammation, eye irritation and temporary blindness, and severe TD requiring emergent medical care. Without medical intervention, TD will last approximately three weeks, but in very sensitive individuals it can last up to 6 weeks (See Figure 3) with significant lifestyle disruption. More clinical images can be viewed at poision-ivy.org.

 

Figure 3. Average time course for mild to moderate allergic contact dermatitis to resolve without treatment. (Figure credit: Zanfel Laboratory, Inc.)

Prevention 

The most common activities for urushiol exposure are: yard trimming (clearing bush, trimming bushes, using a weed eater; gardening (pulling weeds); and other (exposure from pet fur). Suggested options to avoid TD are: 1) avoidance; 2) protective clothing; 3) skin barrier products; and 4) skin (washing) decontamination; 5) oral desensitization and vaccines.

Avoidance

It is recommended to learn how to recognize PIOS and avoid them. For many, this is easy to say, but not practical during military field training, wildland firefighting, search & rescue missions, and wilderness endurance events, or other recreational activities where the plants live. The old adage of “Leaves of three, let it be; Leaves of five, let it thrive; hairy vine, no friend of mine” is an important place to start plant identification for the majority of poison ivy/oak, but not for poison sumac, which has 7-13 leaves (Figure 4). One prevention strategy is to learn leaf pattern, color for each season, and to be able to differentiate them from nonpoisonous look-a-likes, such as the Virginia Creeper (take a plant identification quiz), and other resources for plant identification. Researchers at Duke University state that warmer temperatures brought on by climate change, and increased atmospheric CO2 level promotes greater plant growth and a more toxic form of urushiol. This potentially will affect human health by increasing the occurrence and severity of TD.

Figure 4. Classic leaf identification of poison ivy, poison oak and poison sumac

Clothing

When avoiding these plants is not possible, it is recommended to wear personal protective clothing, e.g., disposable or washable, as a common solution for outdoor occupations. However, caution is needed to avoid urushiol secondary exposure (until clothes are laundered) or from clothing material that does not stop urushiol penetration to skin, e.g., sweaty, thin clothing. Use woven fabric, such as wool. If necessary, consider a waterproof coverall suit. Use heavy duty leather, not cotton gloves, for good protection from urushiol. Depending on protection needs, consider heavy duty vinyl (PVC) gloves since they prevent urushiol penetration, but latex or rubber gloves do not.

Barrier Creams

Although controversial, the evaluation of skin barrier creams, as protective agents prior to exposure to toxic plants, has been investigated for a 20+ years in effort to decrease the extensive hazard in the U.S. Forestry Services and other occupations. In the mid 1990s, it was reported that up to 150 barrier preparations had been evaluated. In 1992, several barrier creams were evaluated in clinical studies and reported to be effective to prevent or reduce TD severity, but they are not commercially available today. Of these barrier creams, only one, topical 5% quaternium-18 bentonite lotion, has been evaluated to prevent or minimize allergic reaction from urushiol exposure. This preparation was approved by the FDA in 1996 as Ivy Block, and was the preferred barrier cream, but unfortunately it was discontinued in ~2018. Currently, there is another purported barrier cream, e.g., Ivy-X, available commercially that claims to be effective, but there is no published randomized clinical trials reporting effectiveness at this time.

Cleaning Skin 

It is paramount to lessen the amount of time and concentration of urushiol on skin in effort to decrease symptom severity, but many lack awareness of when they were exposed. Urushiol is known to be degraded with water. If you are aware, immediately wash exposed skin within 60 minutes. (See Table 1). However, it is still recommended by expert consensus to wash exposed skin up to two hours after urushiol exposure by using repetitive high-pressure, single direction gentle washing with soap (e.g., Dial Ultra or Dawn) and under hot running water. However, this recommendation is not applicable in the outdoors with limited resources. (Note: it is still controversial to use cool, warm or hot water with dish soap to remove urushiol from skin). Based on the evidence, we recommend to use water and dish soap, or wash exposed skin with rubbing (isopropyl) alcohol as a common household product reported for many decades to be effective. The use of rubbing alcohol should be followed by a water rinse, if available. Other recommended household solutions for cleaning urushiol off skin or tools is either mineral spirits, or hypochlorite (dilute 1:9 bleach/water). 

Table 1. Prevention of Toxicodendron dermatitis by cleaning with soap and water.

Commercial skin rinses for urushiol exposure are organic solvents (e.g., deodorized mineral spirits) and are thought to be superior to soap and water. Available products are the classic Tecnu outdoor skin cleanser, Ivy-X post-contact skin cleaner, and Aitex, but they all lack evidence-based research comparing them to household skin decontamination products as mentioned above. Of these three skin rinse solutions, Tecnu skin cleanser has been around since the 1960s and was developed a wash to remove radioactive dust from skin. By chance it was later used for skin decontamination from urushiol exposure and proved to be effective to prevent TD. Even though there is supporting evidence that Tecnu skin cleanser can reduce the chance of ACD developing, this reduction is not significantly more effective than Dial Ultra dish soap and water. The limitation of these rinse products for toxic plants post exposure is that they are expensive options when compared to rubbing alcohol, and soap and water. Consequently, in an outdoor setting we recommend using rubbing alcohol, e.g., carry a small bottle or isopropyl alcohol wipes for post-exposure PIOS skin decontamination. Alternatively, hand sanitizer, such as Germ-X or Purell, contains 62-70% isopropyl alcohol and it is commonly carried today for COVID-19 virus prevention; it has multiple uses to decontaminate skin or use as an antiseptic for soft tissue injuries. 

Oral Desensitization & Vaccines

There is some literature that indicates the use of oral (homeopathic) preparations of PIOS may be protective, but randomized controlled trials are lacking. Some studies suggest hyposensitization can occur, but not for desensitization. This area of investigation remains controversial at this time for any evidence-based research with recommendations to ingest antigens from parts of PIOS without side effects, e.g., skin rashes, or any evidence to desensitization individuals to prevent TD when exposed to urushiol.

There has been long-term interest to develop a vaccine to prevent TD and new clinical trials are underway. The collaborators for the initial clinical trials are Hapten Sciences Inc., ElSohly Laboratories Inc., University of Mississippi School of Pharmacy (personal communication Raymond J. Hage Jr., Chief Executive Officer, Hapten Sciences 27 April 2021). The first of two Phase I clinical trials was completed in 2017. Forty human volunteers were randomized in a double-blind, placebo-controlled study of single ascending dose levels of PDC-APB, a small molecule that acts like a vaccine to prevent TD. The primary objective of the study is to assess the safety and tolerability of PDC-APB following single doses administered intramuscularly to healthy volunteers who are sensitive to urushiol (patch test) between 18 and 55 years old. PDC-APB was reported to be generally well tolerated. A second ascending dose level Phase I study is scheduled to start in July 2021. The outcome of these studies will provide key data for further development in larger trials with the ultimate goal of meeting FDA requirements for a new drug application. Those who will benefit the most from a vaccine to prevent TD are individuals with significant job-related urushiol exposure hazards, and the 10-15% of the population who are severely sensitive to urushiol. 

Treatment

A recent review stated that even with a very high sensitivity and annual exposure to PIOS there are few published well-designed treatment studies of TD. Consequently, management approaches are based on clinical experience. Many individuals eventually seek a clinician for itching, but only after experiencing ineffectiveness with over-the-counter products. See Table 2 for when it is essential to see a clinician for severe signs and symptoms. 

Table 2. When to see a clinician for severe Toxicodendron dermatitis

Most individuals with TD are seen by a family medicine practitioner or other primary care clinicians. Occasionally it is recommended to see a dermatologist for TD that doesn’t improve. The goal in treatment is to decrease the symptoms, e.g., itching, redness, edema, dry weeping lesions, and shorten the time course. For the most common treatment options, see Table 3. See the following for a more in-depth discussion about clinical management options: Toxicodendron Toxicity and Poison Ivy (Toxicodendron) dermatitis.

$ = less than ten dollars; $$ = less than twenty dollars; $$$ = more than twenty dollars.
Table 3. Up-to-date treatment options for mild to severe Toxicodendron dermatitis.

Patient Education

Two resources for patient education about PIOS exposure are provided by UpToDate. One is titled: "The Basics" and is for patients who want a basic level overview. The other is called "Beyond the Basics," a more detailed article written for patients who want greater information. Individuals can get further education about PIOS at an annual poison ivy conference and interact with subject matter experts.

Summary

There is a significant impact annually from exposure to PIOS plants during outdoor occupations, residential yard work, and from wilderness recreational activities. Mild exposure is self-limiting and can be managed with proven over-the-counter medications, such as Zanfel, Burow’s solution, etc. However, for patients with moderate to severe symptoms resulting in extreme discomfort, and poor sleep quality, we recommend seeking a clinician early for systemic and topical steroids prescriptions. An early course of prescription steroids will lessen the symptoms, rash duration, and improve quality of life. The key is to implement prevention steps by using plant recognition, protective clothing, and urushiol skin decontamination. In the future, it will be a tremendous achievement for a FDA approved vaccine for preventive use, particularly for individuals in outdoor occupations, and those with extreme sensitivity to urushiol. 

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