A look at (but no touching) Poison Ivy

It’s that time of year again---visits to the ER by patients who have been in contact with any of the nasty threesome--- poison ivy (Toxicodendron radicans), poison sumac (Rhus vernix) and poison oak (Rhus diversiloba).

According to the American Academy of Dermatologists (AAOD), they are the single most common cause of allergic reactions in the United States as every year between 10 and 50 million Americans develop a rash after contact with these plants.

Poison ivy is found east of the Rocky Mountains, while poison sumac grows in southern Canada, throughout the northeast and midwest. Poison oak is typically found along in the southeast and in the western US. 

“Leaves of three, let it be” is good advice for those wary of poison ivy and poison oak (though botanists clarify that these are actually clusters  three “leaflets” of single leaveson each stem). Poison sumac, commonly found in wet boggy areas, has seven to 13 leaflets (per leaf) all directly opposite one another on the stem except for the one slightly longer one on the end or tip. 

The contact dermatitis is caused by contact with an oil found throughout the plant (throughout the year) called urushiol (you-ROO-shee-ohl). Urushiol is a mixture of catchol derivatives. The major catechol on poison ivy leaves is pentadecylcatechol.

If urushiol is washed off the skin quickly, the reaction can be largely prevented. However, if left on the skin, some diffuses through the skin, where it is metabolized to quinone derivatives. These form covalent complexes with skin proteins such as keratin. These complexes appear foreign to the immune system, which therefore attacks them. Uruahiol typically clear or pale yellow, the oil darkens with prolonged exposure to air. Contact occurs with-- 1) direct contact with any part of the plant, 2) indirect contact as the oil is on another object (gardening tools, animal fur, clothing), and 3) airborne particles when the plant is burned and comes in contact with skin or breathed into the lungs (this is one of the leading causes of disability in forest firefighting teams). Nearly one-third of forestry workers and firefighters who battle forest fires in California, Oregon and Washington develop rashes or lung irritations from contact with poison oak, which is the most common of the three in those states. 

Penetration begins within minutes of contact and the characteristic linear rash accompanied with itching presents within 12-48 hours. Blistering is not uncommon,  and the rash can take 10-20 days or more to resolve.

The rash does not spread itself; first appearing in thin-skinned areas like the face; it appears to be absorbed more slowly in thicker skinned areas with the rash appearing later in these areas---giving rise to the belief that the rash is “spreading.” Reactions seldom occur with the first exposure---second exposures produce a reaction in about 85% of the population. Sensitivity appears to decline with age, some say that the sensitivity is cut in half as children with repeated exposures transition into early adulthood. Immunity is possible through the use of a prescription version of the urishiol—this process can take four months to accomplish and the medication must be continued to sustain the effect. Barrier skin creams containing bentoquatum can be applied prior to exposure (eg. IvyBlock) and provide limited protection. Newer products being developed focus on blocking the absorption of urishiol. 

Post-exposure considerations

If you suspect an encounter with poison ivy, poison oak or poison sumac, follow these simple steps:

•Wash exposed areas with cold running water as soon as you can reach a stream, lake or garden hose. If you can do this within five minutes, the water may keep the urushiol from contacting your skin and spreading to other parts of your body. Within the first 30 minutes, soap and water are helpful.

•Relieve the itching of mild rashes by taking cool showers and applying OTC preparations like calamine lotion or Burrow's solution.* Soaking in a lukewarm bath with an oatmeal or baking soda solution also may ease itching and dry oozing blisters. Over-the-counter hydrocortisone creams are not strong enough to have any effect on poison ivy rashes, according to literature from the AAOD. The FDA considers them effective in managing some of the itching. 

*aluminum acetate (Burrows solution) --baking soda --Aveeno (oatmeal bath) --aluminum hydroxide gel --calamine --kaolin --zinc acetate--zinc carbonate --zinc oxide --manganese sulfate solution --jewel  weed (homeopathic)

Severe reactions can be treated with prescription oral corticosteroids. Phillip M. Williford, M.D., assistant professor of dermatology, Wake Forest University, prescribes oral corticosteroids if the rash is on the face, genitals, or covers more than 30 percent of the body. The drug must be taken for at least 14 days, and preferably over a three-week period, says FDA's Ko. Shorter courses of treatment, he warns, will cause a rebound with an even more severe rash.

•Wash your clothing  in a washing machine with detergent (be careful that you do not transfer the urushiol to any surfaces as you bring the clothing into  the house). Dry cleaning is also effective. Do not forget to clean tents, and hunting and fishing gear---the oil can remain active for many months. 

William L. Epstein, M.D., professor of dermatology, University of California, San Francisco, recommends the following more specific regimen:

1.   Cleanse exposed skin with generous amounts of isopropyl alcohol.        (Don't return to the woods or yard the same day. Alcohol removes your skin's protection along with the urushiol and any new contact will cause the  urushiol to penetrate twice as fast.)

2.     Wash skin with water. (Water temperature does not matter; if  you're          outside, it's likely only cold water will be available.)

3.  Take a regular shower with soap and warm water. Do not use soap before this point because "soap will tend to pick up some of the urushiol from the surface of the skin and move it around," says Epstein.

4.     Clothes, shoes, tools, and anything else that may have been in contact with the urushiol should be wiped off with alcohol and water. Be sure to wear   gloves or otherwise cover your hands while doing this and then discard         the hand covering.

For further information and investigation, consider the following Resources via the Internet:

http://www.poison-ivy-protection.com/

http://www.bio.umass.edu/immunology/poisoniv.htm poison ivy immunology

http://poisonivy.aesir.com/welcome (includes treatment and lots of photos)

http://www.aad.org/pamphlets/PoisonIvy.html   (American Academy of Dermatology)

http://www.fda.gov/fdac/features/796_ivy.html  

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