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Urushiol Oil

 

Author:   Sara E. Mullins

Contributed to Toxipedia as part of the University Partnerships Program.

Overview


Urushiol, pronounced [ (y)o͝oˈro͞oSHēˌôl, -ˌōl, -ˌäl ], is an allergenic oil found in members of the plant family Anacardiaceae. Members of the Anacardiaceae family include poison ivies (Toxicodendron radicans, Toxicodendron rydbergii), poison oaks (Toxicodendron toxicodendron, Toxicodendron diversiloba), and poison sumac (Toxicodendron vernix), as well as some trees such as mango (Mangifera sp), Chinese lacquer tree (Toxicodendron vernicifluum), cashew nut (Anacardium occidentale), and the Indian marking nut (Semecarpus anacardium). The ginkgo tree (Ginkgo biloba) has also been found to have some related allergenic catechols (Rietschel and Fowler 2008, p. 406).

Exposure to plants of the Anacardiaceae family accounts for more allergic contact dermatitis than all other plant families combined. In the United States, the most important members of this family are those of the genus Toxicodendron (previously classified as in the genus Rhus). Toxicodendron means "poisonous tree" (Prok and McGovern 2014).

When their leaf or other plant parts are bruised, damaged, or burned, Toxicodendrons release urushiol oil. When the oil gets on the skin, an allergic contact dermatitis reaction occurs. Most exposed people develop an itchy, red rash with bumps or blisters. Exposure to as little as 50 µg of urushiol is enough to cause a reaction. Depending upon where it occurs and how broadly it is spread, the rash may significantly impede or prevent a person from working. Although over-the-counter topical medications may relieve symptoms for most people, immediate medical attention may be required for severe reactions, particularly when exposed to the smoke from burning these poisonous plants, which can cause irritation to the lungs (CDC 2014).

Species of Toxicodendrons are found in most parts of the continental US as well as Canada and are found in abundance in places such as fields, forests, and around streams. These plants can also be found in urban environments such as backyards and playgrounds, which increases the chance of humans coming into contact with them. The leaflets of the poison ivy and oak plants usually grow in groups of three, giving rise to the warning, “Leaves of three, leave them be!” However, finding species that have more than three leaves in their configuration is not uncommon. There are species of Rhus that also have three leaf configurations but do not exhibit the same allergenic properties that are found in Toxicodendrons. Being able to distinguish Toxicodendrons from others, such as Rhus, is the key to avoiding exposure (CDC 2014).

Chemical Description


 

           Urushiol

 

R = (CH2)14CH3 or
R = (CH2)7CH=CH(CH2)5CH3 or
R = (CH2)7CH=CHCH2CH=CH(CH2)2CH3 or
R = (CH2)7CH=CHCH2CH=CHCH=CHCH3 or
R = (CH2)7CH=CHCH2CH=CHCH2CH=CH2 and others


Molecular Formula: C21H36O2 

Color/Form: Pale yellow liquid

Boiling Point: 200-210 °C

Density/Specific Gravity: 0.968

Solubility: Urushiol is soluble in alcohol, ether, and benzene (Lewis 2001, p. 1155).

History


The name urushiol originates from the Japanese word “urushi” which means lacquer. The Japanese extracted urushiol from the Japanese lacquer tree and used it to coat pottery. When urushiol is oxidized, it leaves a hard coat of lacquer giving the coated pottery the name, lacquerware. Due to its abundance, the exact origin of urushiol is unknown. Some of the first records of poison ivy, a plant containing urushiol, date back to the 1600s. Captain John Smith gave poison ivy its name in 1609 when visiting America, and the plant was taken back to England as an ornamental plant. Poison oak, another plant that contains urushiol, was formally discovered on Vancouver Island by David Douglas in the early 1800s (Dunphy 2015).

Routes of Exposure


Since the body does not have the appropriate antibodies to combat a specific allergen at the time of initial exposure, an allergic reaction does not occur. An allergic reaction to urushiol, usually resulting in dermatitis, will typically occur after the second exposure to the allergen when the body has had the time to build up antibodies to attack the allergen. This buildup of antibodies in the body is called sensitization. This initial sensitization process begins when the antigen is taken up by the Langerhans cells in the skin. The Langerhans cells migrate to the lymph nodes where the antigen is presented to T-lymphocytes. The T-lymphocytes process the urushiol antigen and become specifically reactive to it. These T-cells are now ready to respond the next time the individual is exposed to the allergen (Rietschel and Fowler 2008, p. 1).

Routes of exposure by which one can develop dermatitis from urushiol exposure include direct contact, indirect contact, and inhalation. Direct contact occurs when one’s skin touches or rubs against a bruised or damaged plant containing urushiol. For example, pulling a plant from the ground with one’s bare hands will likely damage the plant and result in direct contact with urushiol. Indirect contact occurs when one touches an object that has been in contact with urushiol. For example, touching a glove that was previously used to pull a plant can result in one’s skin being exposed to urushiol. This exposure can occur years after the gloves were used to pull the plant. Inhalation exposure occurs when urushiol particles become airborne and are subsequently inhaled into the lungs. Burning an area that has plants containing urushiol or burning the plants after removal from the ground puts one at risk for inhalational exposure (Rietschel and Fowler 2008, p. 408-411).

Undamaged or unbruised plants are innocuous. If contact is made, it will not result in dermatitis. This is due to the fact that the plant only excretes urushiol when it is damaged or bruised. After a previously sensitized person is exposed to urushiol, dermatitis usually occurs within two days, but the effects can sometimes be seen in as little as a few hours after exposure (Rietschel and Fowler 2008, p. 408). Urushiol enters the skin so rapidly that one has only ten minutes after exposure to wash it off in order to prevent dermatitis. After the urushiol reacts with the skin, washing will no longer prevent dermatitis, although it may remove excess urushiol that is unreacted, possibly limiting the spread to uncontaminated areas (Lee and Arriola 1999).

Human Health Effects


Approximately 50-70 percent of adults in America are sensitized to urushiol, the allergenic compound found in poison ivy, poison oak, and poison sumac. Annually, an estimated 25 to 40 million Americans will have to seek medical treatment after exposure to urushiol. People who are at a higher risk of becoming exposed to Toxicodendron species and urushiol are those who have outdoor occupations. “Forestry workers and firefighters who battle forest fires are at additional risk because they could potentially develop rashes and lung irritation from contact with damaged or burning poisonous plants” (CDC 2014). Because of the increased risk, the Centers for Disease Control and Prevention recommends that those who have such occupations and their employers take the basic precautions and steps to prevent unnecessary exposure.

Poison ivy dermatitis affects all ethnicities and skin types, and most geographical regions in the United States are at risk. Dermatitis caused by urushiol is not age dependent and also affects children. Most children in the United States have had their first exposure and have become sensitized to urushiol by the age of eight (Prok and McGovern 2014).

Signs and Symptoms


Signs and symptoms associated with dermal contact with poisonous plants containing urushiol may include:

  • Red rash within a few days of contact
  • Possible bumps, patches, streaking, or weeping blisters
  • Swelling
  • Itchy and irritated skin (CDC 2014)

These symptoms usually occur within the first 24 to 48 hours of exposure; and the course of the dermatitis is usually self-limiting, lasting approximately 1 to 2 weeks. Although most cases resolve without significant problems, complications may include secondary bacterial infections and, rarely, skin conditions such as erythema multiforme, a“bulls-eye” rash, and urticaria, or hives (Lee and Arriola 1999).

 

Environmental Health Effects


Since some vines in controlled laboratory studies exhibit enhanced growth with elevated CO2 levels, Toxicodendron varieties might respond similarly. Rising CO2 levels are potentially responsible for the increase in vine growth that is inhibiting forest regrowth and increasing the loss of trees. Experimental evidence shows that elevated CO2 levels increases the growth stimulation of poison ivy more than that of most other woody species and causes these plants to produce a more allergenic form of urushiol. Evidence suggests that the Toxicodendron species will become more abundant and more "toxic" in the future, potentially affecting global forest dynamics and human health (Ziska et al. 2006).

Preventive Measures

The most effective preventative measure is keeping the skin from being exposed while in proximity to urushiol-containing plants. This can be done by the implementation of long sleeves, pants, boots, and gloves, assuming that the gloves used are vinyl. This is necessary due to the fact that the catechols in urushiol are soluble in rubber, making rubber an insufficient form of protection (Rietschel and Fowler 2008, p. 410). If there is a possibility that clothing has come into contact with urushiol, wash the exposed clothing separately in hot water with detergent. Furthermore, to avoid indirect contact, cleaning and washing contaminated tools with either rubbing alcohol or soap and water will decrease the chances of exposure in the future, keeping in mind that urushiol can remain effective for several years on inanimate objects. To avoid inhalation, plants or brush piles that may contain poison ivy, poison oak, or poison sumac must not be burned. Inhaling the smoke from these burning plants can cause a severe allergic reaction and respiratory problems. Additionally, the implementation of various skin creams to create a barrier between the skin and the urushiol oil can provide some protection. For example, Ivy Block, which contains bentoquatam, provides protection for many who are sensitive to urushiol (Rietschel and Fowler 2008, p. 409).

As stated previously, urushiol penetrates and reacts with the skin very rapidly. Therefore, actions must be taken quickly after exposure to minimize the reaction. The affected area must be washed thoroughly with mild soap and water to remove any remaining urushiol that might otherwise be transferred to other areas of the body. Since the allergen remains active on surfaces for a long period of time, contaminated clothing and gear must also be removed as soon as possible and washed.

References

Centers for Disease Control and Prevention. 2014. Poisonous Plants. http://www.cdc.gov/niosh/topics/plants/ [accessed April 4, 2015]

Dunphy, Jim. 2015. Poison Ivy, Oak, and Sumac Information Center. AESIR Computing, Inc. http://poisonivy.aesir.com/view [accessed April 11, 2015]

Lee, N. P., & Arriola, E. R. “Poison Ivy, Oak and Sumac Dermatitis.”  Western Journal of Medicine 171, 5-6 (1999): 354-355.

Lewis, R. J. Sr. Hawley's Condensed Chemical Dictionary. 14th ed. New York: John Wiley & Sons, Inc. 2001.

Prok, Lori, & McGovern, Thomas. 2014. Poison Ivy (Toxicodendron) Dermatitis. Uptodate, Inc. http://www.uptodate.com/contents/poison-ivy-toxicodendron-dermatitis [accessed April 4, 2015]

Rietschel, Robert L., & Fowler, Joseph F. Fisher's Contact Dermatitis. 6th ed. Ontario: BC Decker, Inc., 2008.  

Ziska, L. H., Sicher, R. C., George, K., & Mohan, J. E. “Rising Atmospheric Carbon Dioxide and Potential Impacts on the Growth and Toxicity of Poison Ivy (Toxicodendron Radicans).” Weed Sciences 55, 4 (2007): 288-292.

 

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