Leaves of Three

August 1, 2002
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It lurked just a few feet away, poised to deliver misery to the campers as they prepared lunch. That is how it attacks, silently, without warning. It blends so well into the scene, green and lush, winding around the pine tree in such an innocent fashion. Without so much as a sound it will deliver the toxin to its victim, who needs only to touch the plant.

Poison oak and its close cousin, poison ivy, are in abundance in many parts of the country. In the southeast it carpets the forest and has a resilience that can only be compared to that of the common cockroach. In the West, poison oak is a scourge for mountain climbers, hikers and campers alike.


For most people, the two plants are indistinguishable. Both normally grow with three leaflets on a single stem, but may have up to 11 leaflets. Poison ivy leaflets are usually oval and lightly toothed. Poison oak leaflets are usually slightly lobed, like oak tree leaves. But the two plants can hybridize where their ranges overlap, and plants from rootstocks may produce different leaflet shapes than plants grown from seeds. Fortunately, both have leaflets approximately 4 inches long, with woody stems, and waxy (they can be dull or hairy underneath) leaves that start out bright green and turn yellowish or reddish, then bright red, toward late summer and fall.

Poison ivy is a vine, growing across open ground or twining its way up shrubs and trees. It is a hardy plant that can grow on limited amounts of soil and moisture. It can sprout and adapt to a rock crevice, making it a danger for rock climbers. The vine is a prolific spreader as well, putting down roots wherever a leaf-stem junction makes contact with soil. It seems to grow well in shade or full sun, and it thrives on most soil types from sea level to 5000 feet elevation. It will grow in the crack of a city sidewalk as readily as in a lush forest.

Poison oak adds insult to injury because of its ability to adapt to its surroundings. It may grow as a bush with upright stems, attach itself to a tree with hair-like roots or creep along the ground in an open meadow.

Poison sumac has a different leaf formation than poison oak and ivy. It’s far more similar to the other members of the sumac family. The leaves are pennate with each cluster of leaves 8 to 12 inches in length. The poison variety favors the damp soil of swamps, bogs, seepage slopes and frequently flooded areas. The sumac sap turns black upon contact and begins to cause a rash almost immediately.

The nature of the poison sumac’s habitat tends to limit human contact. Considered by some sources as one of the most dangerous North American plants, the poison sumac grows primarily east of the Mississippi River.

These poison plants are more than just a scourge to the camper. According to the Mining Safety and Health Administration, contact with poison ivy, poison oak and poison sumac, each of which causes urushiol poisoning, is the greatest single cause of worker’s compensation claims in the mining industry.


The toxin from the plants is a sticky substance, yet it isn’t so sticky that it can easily be noticed. The toxin attacks the victim and causes irritation as it penetrates the outer layer of the skin cells. In normal cases, the time required to begin the process is roughly 20 minutes. The typical reaction is an area of small blisters and the aggravating itch that accompanies them.

Avoidance is the best preventive. If the plant is not touched, it cannot be harmful, right? Well, not exactly. The smoke from the burning plant can contain the toxin as well. Thus, inhaling the smoke can cause the irritation to occur inside the nasal passages, lungs or throat. This is most dangerous to those persons with a high sensitivity to the toxin, as it can lead to severe respiratory problems.

Touching the plant or breathing the smoke are by far not the only means of contact, however. Handling clothing that has been in contact with the plant or even petting an animal that has walked through the leaves and stems can cause the toxin to be spread to humans. Even something so innocent as rolling a sleeping bag and putting it away can transfer the toxin from the plant to the bag and then to the skin.

It has even been noted that firemen and rescue personnel who have come in contact with poison oak toxin in the mud around a landslide, have developed the rash. Another example of the resiliency of the toxin is its ability to lie dormant for months, even years. The toxin can attach itself to a tent, shovel or axe handle, a sleeping bag or even a boat cushion, be stored and then infect an unsuspecting camper the next time the equipment is pulled out for use.


Washing affected areas thoroughly with soap and water is one of the best solutions to the problem of urushiol contamination. If contact is suspected, wash the affected area as soon as possible. The cooler and drier the skin, the more time you have to wash away the toxin. The hotter and sweatier the skin, the faster the toxin can react. This is one reason some people are lulled into thinking that they are not “allergic” to the plant. Few people, if any, are completely immune to the toxin.

Now that we know the common ways the toxin comes into contact with skin, we need to look at some of the treatments for the itching and blistering that can follow. First of all, if the smoke of burning plants has been inhaled and any symptoms of respiratory distress appear, contact a physician immediately.

For the skin rash, a number of topical lotions, creams and ointments are available over the counter. Calamine lotion – the chalky flesh-colored stuff with the very distinctive odor – is still the most common treatment for poison ivy and poison oak rash. However, today there is also an assortment of clear lotions, soothing creams and even cooling sprays that relieve the relentless itching.

The probability of the rash turning into a secondary skin infection is increased when the victim scratches the rash. That’s the primary reason to treat and dry the rash as quickly as possible. Severe rashes caused by poison oak, ivy or sumac should be treated immediately by a physician, especially those cases affecting the face and head.

Poison sumac may be comparatively rare, but poison ivy and oak are prevalent across the United States at a time when people are enjoying the great outdoors. Simple avoidance is the best preventive, so just remember, “leaves of three, leave them be.”


According to William L. Epstein, M.D., Professor of Dermatology, University of California, San Francisco, if you’ve been exposed to poison ivy, oak or sumac, stay outdoors until you complete the first two steps, if possible:

First, says Epstein, cleanse exposed skin with generous amounts of isopropyl (rubbing) 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.

Second, wash skin with water. Water temperature does not matter; if you’re outside, it’s likely only cold water will be available.

Third, 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.

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.

The rash will only occur where urushiol has touched the skin; it doesn’t spread throughout the body. It may appear to spread over time, but this is either because the urushiol is absorbed at different rates in different parts of the body or because of repeated exposure to contaminated objects or urushiol trapped under the fingernails. The rash, blisters and itch normally disappear in 14 to 20 days without any treatment. For mild cases, wet compresses or soaking in cool water may be effective. Oral antihistamines can also relieve itching. The Food and Drug Administration (FDA) also considers over-the-counter topical corticosteroids (commonly called hydrocortisones under brand names such as Cortaid and Lanacort) safe and effective for temporary relief of itching associated with poison ivy.

For severe cases, prescription topical corticosteroid drugs can halt the reaction, but only if treatment begins within a few hours of exposure. “After the blisters form, the [topical] steroid isn’t going to do much,” says Epstein. The American Academy of Dermatology recommends that people who have had severe reactions in the past should contact a dermatologist as soon as possible after a new exposure.

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