Toxicodendron diversilobum

The old adage - "Leaves of three, let it be; berries white, poisonous sight" - is useful, but there are a number of plants with 3 leaflets growing in the same areas as poison-oak. The best way to recognize this plant is the 3-part leaf whose central leaflet has a distinct petiole (leaf stem) as circled in orange above.

Though the Eastern US species of Toxicodendron was first noted by Captain John Smith in the early 1600s, Western poison-oak was noted by another British explorer of the 19th century, Captain Frederick Beechey. Much to the chagrin of unwary gardeners, he took samples back to England! Both poison oak and poison ivy were planted in English gardens for their graceful climbing habit and beautiful fall foliage (you can probably guess the rest). Many newcomers to California also admire the handsome shiny leaves and red coloration of this species, occasionally leading to equally unfortunate contact.

Yes, few would intentionally wish to add this shrub/vine to their gardens. Indeed, most would like to know how to remove it! On large properties bordering wildlands, unless you need routine access into or through areas where poison-oak is growing, avoidance is perhaps the most prudent. Management and removal are possible but should be approached with extreme caution (see References at the end of this page). Burning poison-oak is ill-advised as the harmful (but non-volatile) oils can then become airborne and enter the throat, lungs, or intestines, causing the most severe reactions.

Though many people believe that they may be 'immune' to poison-oak, 80-90% of the world's population can become sensitized to the active chemical, urushiol, which is found in the resin canals and leaf surfaces of the plant (it is absent from pollen or honey made from the flowers). Except for highly sensitive individuals, the allergic reaction generally occurs after one or more exposures to the oil (usually unknown to the individual).

Within 15-30 minutes after contact with poison-oak, heptadecylcatechol molecules contained within the oil penetrate the epidermal layer of the skin then oxidize and bind onto cell proteins. Immediately washing exposed skin after exposure is advised, using special soaps or rubbing alcohol, which dissolves the oil more easily, to minimize binding of the urushiol. There are also skin creams which help prevent urushiol binding when exposure is likely or expected (see References at the end of this page).

At the point of binding to your body's cells, the oxidized heptadecylcatechol molecules are virtually impossible to remove, and, contrary to popular belief, cannot be spread by scratching the rash or spreading released blister fluids. Oils remaining on clothing, pet fur, or other items can 'infect' innocent bystanders who were not in direct contact with poison-oak and/or re-infect the individual who was (immediate standard laundering is highly recommended).

The rash may continue to form in new places after the initial onset because of a delayed reaction of the molecules and the body's reaction to them. Except in severe cases (for which medical help should be sought) the rash will dissipate in one to four weeks, depending upon the rash extent. Once you've had this rash you are more 'sensitized' to a repeat occurrence if exposed to urushiol in future - this is due to the now increased number of white blood cells created by your body to react to urushiol (thereby causing the rash).

'Remedies' for poison-oak rash generally address relieving the symptoms of the rash (again see References at the end of this page for various suggestions). Gently dabbing with rubbing alcohol helps cool and sooth the itch. California native indians used the white gummy substance found in the floral buds of Gumweed, Grindelia camporum similarly, or made a poultice from boiled leaves and flowers. The first white immigrants recorded this practice and no doubt used it themselves.

This author, while touring in the wooded countryside behind Nice, was surprised at how similar this French landscape looked to areas of California. After a few moments I realized that the main reason for this mental comparison was the reddish foliage that would appear occasionally. This turned out to be the closely related Cotinus coggygria, Smokebush, another member of the Anacardiaceae which contains smaller amounts of urushiol and it generally not regarded as a potential threat. Be that as it may, there do seem to be cases where individuals who have become sensitized to urushiol via poison-oak also showed a new sensitivity to Smokebush and other members of the Anacardiaceae.

It's all over California, especially the Bay Area! It is insidious, creeping up on you when you least suspect it. And it's miserable to deal with. The diabolical skin rash we call poison oak can affect anyone at anytime of the year. In California, the rash is caused by poison oak, in the Midwest and East coast it's caused by poison ivy, and in the South it's caused by poison sumac. But whatever the cause, the reaction is generally the same. It is triggered by an oil [called urushiol]. And the reaction of this oil to your skin will lead to the typical rash we see. This rash can occur on any skin that has contact with the oil. The rash can occur within two days of exposure to the oil, or as long as two weeks if this is your first exposure.

Initial symptoms are skin irritation followed by itching and blister formation. The rash can be pretty extensive and may be spread by touching the initial exposure site and spreading the oil to other parts of the skin. Often the rash is seen in a linear deposition due to the patient scratching the skin in a line.

The best thing to do if you know you have been exposed to poison oak is to immediately wash all exposed skin with rubbing alcohol in which the resin in soluble. Soap works also but not as well. And rinse with cold water that will not open the skin pores to the oil.

Once the rash appears, the horse is out of the barn and no washing will help. However, contrary to popular belief, the fluid from the blisters and skin vesicles cannot spread the rash. But you must be careful not to touch any clothes that may still have the oil and be ure to wash the clothes thoroughly to get rid of the oil.

Treatment of poison oak consists of cool compresses to sooth the rash. Antihistamines like Claritin or Zyrtec can be helpful to minimize the itching. And these antihistamines should not cause drowsiness like the older ones do such as Benadryl.

However if the poison ivy or poison oak is moderate, severe or more extensive, a visit to your doctor may be warranted. They can prescribe potent topical steroids to the affected areas or if the rash is extensive enough than oral steroids. These medications will suppress the allergic reaction caused by the oil on the skin. In two or three days, the itching should subside and the rash should start to recede. However it is crucial to take these meds in tapering doses over two to three weeks to prevent a recurrence of the rash.

Some researchers have tried to desensitize patients to poison ivy and poison oak by giving them increasing dosing of the oil over a period of time. This has been less than successful and complicated with intolerable side effects such as outbreaks in the GI tract. They are usually reserved for those highly sensitive or people who cannot avoid contact such as forest rangers.

A better approach would be learning to recognize the plant and avoiding contact with it. Staying on a well marked trail wearing long pants and shoes have helped. If accidental contact occurs then wiping the oil with alcohol or alcohol based beverages can help. Using barrier creams such as Ivy Shield or Ivy Block may help prevent outbreaks of the rash. But old fashion vigilance in identifying the plants and avoiding it is the best approach to preventing contracting this annoying and intolerable skin rash.

Each year, poison oak and poison ivy cause about two million cases of skin poisoning serious enough to require either medical attention or at least restricted activities. Poison oak poses a serious risk to firefighters, according to Jerry Jeffries, safety and health specialist at the Missoula Technology & Development Center. It's an extremely disruptive problem, says Jeffries. Depending on the fire season, it can affect thousands of people. We have to send people home, because they get sick and we have to get them away from the fire line.

Respiratory emergencies resulting from inhalation of dust or smoke from burning plants are extremely rare among the general population, but common with firefighters. Immediate attention is required, and treatment should include maintaining a patent airway and administering intravenous corticosteroids. We have the problem of getting poison oak stands on fire, says Jeffries. Then firefighters inhale the smoke and get it in their lungs. It causes blisters, which break and run. The heavy particles of the smoke contain the poisonous resin; it falls down in soot form. When it's inhaled, the lungs swell, causing coughing and extreme irritation and swelling in the throat. It makes breathing near impossible, and can be life-threatening.

I have never had a poison oak rash, despite living in and around it much of my life. I do not know if I have been fortunate not to touch any or not, but I find that hard to believe since my nearest brother gets terribly infected by the least brush with it. My father was immune until he brushed an open cut with it my accident, and now is sensitized. However, when growing Ceanothus maritimus 'Valley Violet', a UC Davis Arboretum introduction in my thesis project, I discovered that the slightest brush with that will leave raised, red rashy trails wherever I rub against it. Unlike poison oak, though, they appear fairly quickly, and are gone within about 3 days. I don't know if there are hairs or chemicals involved, but I have learned to wear long sleeves when doing anything near it!

I seem to be one of the lucky ones and have never had a case that I know of. This insensitivity is particularly obvious when one realizes that I did archaeological surface surveys for thirty years, all over our county. I was probably in minor contact with it quite often. Because of [my wife's] sensitivity, when I returned from these junkets I would enter the garage through the side door, go to the washer, strip and wash everything except my shoes, then streak through the house, holding the shoes appropriately, hoping she wasn't entertaining a bunch of her women friends!

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