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Poison Ivy, Oak, and Sumac Information
Leaves of three, leave it be!

Fast Facts

*Urushiol Oil is Potent

  • Only 1 nanogram (billionth of a gram) needed to cause rash
  • Average is 100 nanograms for most people
  • 1/4 ounce of urushiol is all that is needed to cause a rash in every person on earth
  • 500 people could itch from the amount covering the head of a pin
  • Specimens of urushiol several centuries old have found to cause dermatitis in sensitive people.
  • 1 to 5 years is normal for urushiol oil to stay active on any surface including dead plants
  • Derived from urushi, Japanese name for lacquer
When the Japanese restored the gold leaf on the golden Temple in Kyoto, they painted the urushiol lacquer on it to preserve and maintain the gold. Guess you could say that you would be caught red handed if you stole it.

*Poison Ivy, Oak, and Sumac

  • Most common allergy in the country claiming half the population
  • Sensitivity to urushiol can develop at any time
  • Solutions or cures are those that annihilate urushiol
  • Everyone appears to react slightly different to all the remedies.
  • Covered by workers compensation in some states (CA, for example)
  • First published records of poison ivy in North America date back to 1600s
  • Poison Ivy coined by Captain John Smith in 1609
  • Western Poison Oak discovered by David Douglas (1799-1834) on Vancouver Island. Douglas fir also named after him.
  • People will serious deficiency in cellular (T-cell) immunity such as AIDS patients may not have problems with dermatitis.

*Myths vs. Facts

Myth Fact
Poison Ivy rash is contagious. Rubbing the rashes won't spread poison ivy to other parts of your body (or to another person). You spread the rash only if urushiol oil -- the sticky, resinlike substance that causes the rash -- has been left on your hands.
You can catch poison ivy simply by being near the plants Direct contact is needed to release urusiol oil. Stay away from forest fires, direct burning, or anything else that can cause the oil to become airborne such as a lawnmower, trimmer, etc.
Leaves of three, let them be Poison sumac has 7 to 13 leaves on a branch, although poison ivy and oak have 3 leaves per cluster.
Do not worry about dead plants Urushiol oil stays active on any surface, including dead plants, for up to 5 years.
Breaking the blisters releases urushiol oil that can spread Not true. But your wounds can become infected and you may make the scarring worse. In very extreme cases, excessive fluid may need to be withdrawn by a doctor.
I've been in poison ivy many times and never broken out. I'm immune. Not necessarily true. Upwards of 90% of people are allergic to urushiol oil, it's a matter of time and exposure. The more times you are exposed to urushiol, the more likely it is that you will break out with an allergic rash. For the first time sufferer, it generally takes longer for the rash to show up - generally in 7 to 10 days.

Poison Oak

What does poison oak look like?

Western poison oak, in the form of a bushy shrub or a climbing vine, can be found from Western Canada to Mexico. Poison oak grows from sea level to 5,000 feet of elevation. Characterized by alternate leaves with three or occasionally five veined, shiny leaflets, poison oak thrives throughout California. In the autumn, the leaves turn a deep red color.

Exposure to the oily sap contained in all parts of the poison oak - roots, stem, leaves, flowers, and the fruit (berries) - may cause skin irritation ranging from mild to severe. Between 50% and 85% of the population is allergic to poison oak, resulting in a more severe reaction when exposed.

Primary contamination results from contact with bruised or broken plant parts that release toxicodendrol, an oily resin containing the toxic chemical urushiol. Because the lacquer-like resin does not dissolve in water, it is difficult to wash off and its toxicity persists for a long time. Poison oak branches left on a garage roof for 18 months were found to be toxic. Twigs kept in water for 16 months were still active. Unwashed contaminated clothing retained toxicity for more than one year.

What symptoms does poison oak cause?

Severity of poison oak skin reaction depends on the degree of patient sensitivity, the amount of exposure, and on which body parts are exposed. Eyes, lips, genitals and other sensitive body parts exposed to poison oak sap will experience a more severe reaction.

Skin irritation characterized by redness, blistering, swelling and severe itching generally develops 24-48 hours after the exposure. Some victims experience symptoms after as little as 30 minutes. Others may not have symptoms until two weeks after their exposure.

In typical cases, the reaction is most severe five days after the exposure. Mild cases of poison oak last from seven to 10 days. Severe cases may last up to three weeks or longer. Fair-skinned people are more susceptible than dark-skinned people and younger people are more susceptible than older people.

CAUTION: Burning poison oak can result in a dangerous smoke that can cause severe symptoms to the eyes, nose, throat and lungs.

How contagious is poison oak? How is it spread?

Fluid in the blisters does not contain the toxic poison oak chemical, urushiol. If the blisters break, the fluid will not cause the poison oak to spread.

Scratching other parts of the body with contaminated fingernails can spread poison oak. The toxic chemical can remain under the nails for several days unless carefully removed by thorough cleaning of the nails.

A person who has washed thoroughly and has changed into clean clothing cannot spread poison oak. The only way to become a victim of poison oak is to make direct contact with the toxic resin. This is possible by coming in contact with a contaminated person who has not washed properly or changed into clean clothes.

Other secondary exposures may result from simply handling garden tools, hunting or sports equipment, or camping gear exposed to poison oak. Thick fur protects most pets that run through poison oak patches from developing symptoms. But people who touch contaminated animals can come directly in contact with the toxic resin and can develop poison oak.

How do you treat poison oak?

Treatment consists mainly of protecting the damaged skin, preventing infection and relieving the itching. The pharmacist at your local pharmacy will be happy to help you select the best over-the-counter medications to treat poison oak. Store-brand or generic versions of these medications also work and are usually available.

If the case of poison oak is severe, the patient should see a physician for more extensive treatment with stronger steroid medications.

Avoid the use of older Caladryl® that contains the ingredient "diphenhydramine," unless directed by your physician. Applying diphenhydramine to open sores and taking diphenhydramine by mouth can cause a build-up of the drug leading to toxic symptoms.


  • Learn to recognize poison oak and teach children at an early age to recognize it as well. Leaves of three, let it be.
  • Wear protective clothing when out in the wild.
  • Keep pets from running through poison oak areas.
  • As soon as possible after an exposure, thoroughly wash the affected areas with soap and cool water. Rinse with copious amounts of cool water. (Warm water supposedly enhances the penetration of the oily sap.)
  • Using rubbing alcohol (isopropyl alcohol) on affected skin areas and rinsing with copious amounts of cool water is said to prevent skin irritation.
  • Unfortunately, urushiol binds so strongly to the skin that washing more than 15 minutes after exposure does little to remove the chemical from the skin.
  • Change clothing as soon as possible after exposure and handle contaminated clothing carefully to avoid spreading the poison oak.
  • Launder clothes several times before re-wearing.
  • Never burn poison oak.
  • Apply cool soaks or compresses to reduce itching and decrease heat from inflamed areas. Exposure to hot water increases itching.
  • Do NOT wash the body with liquid bleach after a poison oak exposure. Bleach is not helpful and the vapors can be irritating to the eyes, nose, throat and lungs. Bleach will irritate inflamed skin even more, causing redness and pain to sensitive body parts.
  • Be prepared for an exposure by including hydrocortisone cream and oral antihistamines in your first aid kit when hiking or camping. Check with your pharmacist for selection and use of these products.

California Poison Control System
1-800-876-4766 . . Anytime, Anyplace in California

Poison Ivy

poison ivy leaves
Poison Ivy

Common Name:
Poison Ivy

Scientific Name:
Toxicodendron radicans

Favorite Habitat:
Woodland edge

W hen exploring the woods and fields of the Great Plains, a curious naturalist will usually be on the lookout for dangerous animals such as skunks or venomous snakes, but might not give any thought to the possibility of encountering a dangerous plant.  Of course, plants cannot "attack" a person, but some plants can cause harm if they are touched.  One plant that should definitely be avoided is Poison Ivy, and that can be a real challenge because it grows in different forms, does not have a consistent leaf shape and there are some plants in the same habitat that look like it!

Poison Ivy is a woody vine or sub-shrub that has a very wide distribution.   It may be found coast to coast from southern Canada to Mexico.  It is also known from the West Indies and China.  It is a member of the Anacardiaceae, or Cashew, family.  Most members of this plant family have a tropical or sub-tropical distribution.  In North America, it is represented by the Sumacs (Rhus sp.), Poison Ivy, Poison Oak, Poison Sumac and the Florida Poison Tree (Metopium toxiferum).

Poison Ivy is a nuisance because it contains a chemical that can cause the skin of persons sensitive to it to develop a red, itchy rash and even erupt in blisters.   Urushiol is the active ingredient in Poison Ivy that causes the rash and irritation.  It is present in all parts of the plant, but particularly in the sap.  People vary in their sensitivity to urushiol.  Some have no problem with it and others experience severe allergic reactions.  This can also vary over the life of a person.  You might be unaffected as a child and become sensitized with repeated exposures.  So even if you are not allergic now, it is a good idea to learn how to recognize Poison Ivy in case your body changes as you age.

The clinical name for the skin irritation caused by Poison Ivy is Rhus Dermatitis.  It usually starts as itching and small blisters within a few hours after exposure.  Depending on how strong the exposure was and/or how sensitive the person is, that may be all there is to it.  However, it may develop into an inflamed, swollen rash with open, weeping sores that persists for up to two weeks.   Severe cases may require a visit to the doctor.  Urushiol is absorbed into the skin within three minutes of exposure.  If it is washed off quickly with dishwashing soap and water, the consequences will be less, but you are seldom close to a lavatory when you get exposed, so learning to recognize and avoid it is the best strategy.  An important fact to remember is that the urushiol can travel on your clothes or the fur of your pets, so remember to wash them too if you suspect they were in contact with Poison Ivy.

Poison Ivy grows in a number of different ways:
As a ground cover - It can creep across the ground surface and make a knee-high thicket of foliage.  This is what is shown in the picture at the top of the page.
As a skinny free-standing "shrub" - It can grow in the open with one stem and only a few side branches.  It may be up to ten feet tall in this form, and this is the form that people call Poison Oak.  (According to the experts, Poison Oak is a distinct species that doesn't occur on the prairie [see below], but for all practical purposes they look the same and BOTH should avoided.)  
As a vine - Using thin, brown, aerial roots, it can attach itself to the side of a tree or other object and reach high into the sky.  This is the form where it reaches it greatest size.  It is not uncommon to find vines as thick as your arm growing up the side of large trees.

Poison Ivy is often confused with another woody vine, Virginia Creeper (Parthenocissus quinquefolia).   Notice how much bigger and lighter colored the tendrils of Virginia Creeper are compared to the aerial roots of Poison Ivy.  Both the vines shown below are about as big around as your thumb, and were growing on the same tree. 

poison ivy rootlets
Poison Ivy (don't touch!)
Virginia creepe rootlets
Virginia Creeper (OK to touch)
The fruits of Poison Ivy are grapelike clusters of tiny, white, pumpkin-like seeds with an off-white or pale yellow rind.  The photo below was taken in mid-November and shows that the rind dries out and flakes off eventually.  The fruits also contain urushiol, but that does not stop the birds from eating them!   Flickers and other woodpeckers are fond of them, along with sapsuckers, thrushes, pheasants and quail.  The rind provides food to the birds while the seeds usually pass on through their gut unharmed and, in this way , birds are the agent for dispersal of Poison Ivy seeds.

poison ivy berries
Poison Ivy berries


Poison Ivy has variable leaves:
Poison Ivy has compound leaves.  That is, each leaf is made up of distinct parts, called leaflets.  In this case there is one leaflet at the end of the leaf stalk (or petiole) and two leaflets opposite each other below the first.  This is called a trifoliate pattern.  The two lower leaflets have very short stalks and are often shaped like  mittens, with a lobe on one side.

The shape, color and texture of the leaflets is highly variable.  These shown on the right have fairly smooth margins, but others may have rounded teeth or lobes.

poison ivy leaf


Several other plants look like Poison Ivy:

All the following woody plants have trifoliate leaves and may be found in the Great Plains.

Aromatic Sumac (Rhus aromatica) Also known as Skunkbush, Aromatic Sumac forms dense thickets up to 7 feet tall.  It is native to the eastern half of the U. S. and is often used for landscaping purposes and stabilizing eroding slopes.  In the wild, it will be found on rocky outcroppings and fence rows.  Its berries are red and densely hairy and form in dense clusters.   While in the same family as Poison Ivy, it does not contain urushiol.
Box Elder (Acer negundo) A member of the Maple family, Box Elder has leaves that strongly resemble Poison Ivy in spring, but later in the year has leaves with 5 - 7 leaflets.  Also, its leaves are directly opposite each other on the twigs, while those of Poison Ivy are alternate.  It becomes a medium sized tree and has the typical paired, winged seeds that are common to Maples.  It does not contain urushiol.
Eastern Poison Oak (Toxicodendron toxicarium)   The range of Eastern Poison Oak includes eastern Oklahoma and the adjacent counties in southeast Kansas.  It is otherwise absent from the Great Plains.  Its leaflets are smaller and have more lobes than those of Poison Ivy and it always grows in a shrubby form.  Its fruits are similar to those of Poison Ivy, but usually hairier and larger.  It does contain urushiol and should be avoided.
poison ivy fall leaf Poison Ivy leaves turn a vivid red color in the fall.  It is usually one of the first plants to change.  This touch of beauty on the landscape is, perhaps, a small repayment for all the misery it causes!

California Poison Control System
1-800-876-4766 . . Anytime, Anyplace in California

Back to Begining of Poison Ivy

Poison Sumac

Poison Sumac is not something that we here in the western part of the country need to worry about. It is a problem on the eastern side of the U.S. However in case you are heading back east, here is a little information about the plant.

Poison Sumac (Toxicodendron vernix or Rhus vernix) is a woody shrub growing to 3 m tall. All parts of the plant contain a toxic resin called urushiol that causes skin and mucous membrane irritation to humans. The leaves are pinnate, 25-50 cm long, with 7 - 13 leaflets; the leaflets are 4-10 cm long and sometimes mistaken for individual leaves. The veins from which the leaflets grow are always red. The fruit is a small white or grey berry, produced in panicles 10-20 cm long; this distinguishes it from other sumacs which have red berries.

Poison sumac grows exclusively in very wet or flooded soils, usually in swamps and peat bogs, in the eastern United States and Canada.

In the U.S., it can grow as far west as Wisconsin, where it is found only in the southern part of the state. In the U.S., it is listed under the Federal Noxious Weed Act of 1974, as amended (7 U.S.C. 2801 et seq.), as a "noxious weed". Most U.S. states list this plant in similar categories. It is considered one of the "U.S. Invasive Weeds".

Poison Sumac

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