Rhus toxicodendron (Poison ivy) is a plant in the family Anacardiaceae. The name is often spelled "Poison-ivy" to indicate that it is not a true Ivy or Hedera. It is a woody vine that is well-known for its ability to produce urushiol, a skin irritant that causes an itching rash for most people, technically known as urushiol-induced contact dermatitis. In extreme cases, corticosteroids can be used to treat rashes.
The reaction caused by poison ivy, urushiol-induced contact dermatitis, is an allergic reaction. For this reason some people do not respond to the "poison" because they simply do not have an allergy to urushiol. However, sensitivity can develop over time. For those who are affected by it, it causes a very irritating rash. If poison ivy is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty. If poison ivy is eaten, the digestive tract and airways will be affected, in some cases causing death.
Urushiol oil can remain viable on dead poison ivy plants and other surfaces for up to 5 years and will cause the same effect.
Urushiol-induced contact dermatitis (also called Toxicodendron dermatitis and Rhus dermatitis) is the medical name given to allergic rashes produced by oil urushiol, which is contained in various plants, including the plants of the genus Toxicodendron (including poison ivy, poison oak, and poison Sumac), as well as other plants in the family Anacardiaceae (mango, Rengas tree, Burmese lacquer tree, India marking nut tree, and the shell of the cashew nut), and even unrelated plants such as Ginkgo biloba.
Symptoms of the rash include itching, inflammation, oozing, and in severe cases a burning sensation. The American Academy of Dermatology estimates that there are up to 50 million cases of urushiol-induced dermatitis annually in the United States alone, accounting for 10% of all lost-time injuries in the United States Forest Service. Poison oak is a significant problem in the rural western and southern U.S., while poison-ivy is most rampant in the eastern U.S. Dermatitis from poison sumac is less common, but just as problematic.
Urushiol-induced contact dermatitis is contracted by contact with a plant or any other object containing urushiol oil. Chemically, urushiol is harmless to humans, but when it bonds to skin cells it initiates a T-cell mediated immune response. This immune response is directed towards the complex of urushiol derivatives which are bound up in the skin proteins. The result is an allergic eczematous contact dermatitis characterized by redness, swelling, papules, vesicles, blisters, and streaking. People vary greatly in their sensitivity to urushiol. It is thought that about 20 to 40% of individuals are not significantly affected by it, although at least 25% of the CPE have strong reactions to poison ivy. Since the skin reaction is an allergic one, people may develop an increasingly strong reaction after repeated exposures, or show no immune response on their first exposure, but show definite sensitivity on following exposures.
Normally, it takes about twenty-four hours for the rash to first appear. Although it may worsen during the next few days and may appear to spread, in fact what is happening is that areas that received a lesser dose are latently reacting. The rash takes one to two weeks to run its course, but normally does not leave scars. Severe cases will have small (1-2 mm) clear fluid-filled blisters on the skin. Pus-filled vesicles, containing a whitish fluid, may indicate a secondary infection. Most poison ivy rashes, without infections, will self-resolve within 14 days without treatment. Excessive scratching may result in secondary infection, commonly by staphylococcal and streptococcal species. These may require the use of antibiotics.
The causative agent, urushiol, does not spread once it has bound with a cell membrane, and it is not found in weeping blisters. Thus, once the oil and resin has been thoroughly washed from the skin, the rash is usually not contagious.
|
|
|
