Randy Jacobs, M.D. Patient Education

To return to the Patient Education page and read more articles, click here.

Poison Plant Rashes





Poison Plants: Ivy--Sumac--Oak. Also known as poison ivy in the East, poison oak in the West and poison sumac and ivy in the South -- grow practically everywhere in the United States, except Hawaii, Alaska and some desert areas of Nevada. They are the single most common cause of allergic reactions in the United States and will affect ten to 50 million Americans every year. Poison Oak In the East it grows as a shrub. In the West it may grow as a vine as well as a shrub. Hair is found on the fruit, trunk and leaves. Poison Ivy In the East, Midwest, and South, it grows as a vine. In the Northern states, Canada and around the Great Lakes, it grows as a shrub. Poison Sumac grows in standing water in peat bogs in the North and in swampy areas in parts of the South. Each leaf has 7-13 leaflets. For the sake of convenience, poison ivy in this discussion will refer not only to ivy but to sumac and oak as well. Poison Ivy Rash: Poison ivy rash is really an allergic contact dermatitis caused by a substance called urushiol, (you-ROO-shee-ol), found in the sap of poison ivy, poison oak and poison sumac. Urushiol is a colorless or slightly yellow oil that oozes from any cut, or crushed part of the plant, including the stem and the leaves. You may develop a rash without ever coming into contact with poison ivy, because the urushiol is so easily spread. Sticky, and virtually invisible, it can be carried on the fur of animals, on garden tools, or sports equipment, or on any objects that have come into contact with a crushed or broken plant. After exposure to air, urushiol turns brownish-black, making it easier to spot. It can be neutralized to an inactive state by water. Once it touches the skin, the urushiol begins to penetrate in a matter of minutes In those who are sensitive, a reaction will appear in the form of a line or streak of rash (sometimes resembling insect bites) within 12-48 hours. Redness and swelling will be followed by blisters and severe itching. In a few days, the blisters become crusted and begin to scale. The rash will usually take about ten days to heal, sometimes leaving small spots, especially noticeable in dark skin. The rash can affect almost any part of the body, especially areas where the skin is thin; the soles of the feet and palms of the hands are thicker and less susceptible.


Recognizing Poison Ivy

Identifying the plant is the first step toward avoiding poison ivy. The popular saying "leaves of three, let them be," is a good rule of thumb, but it's only partially correct. Poison oak or poison ivy will take on a different appearance depending on the environment. The leaves may vary from groups of three, to groups of five, seven, or even nine. Poison oak is found in the West and Southwest, poison ivy usually grows east of the Rockies, and poison sumac east of the Mississippi River. The plants grow near streams and lakes, and wherever there are warm, humid summers. Poison ivy grows as a low shrub, vine or climbing vine. It has yellowgreen flowers and white berries. Poison oak is a low shrub or small tree with clusters of yellow berries and the oak-like leaves. Poison sumac grows to a tall, rangy shrub producing 7-13 smooth edged leaves, and cream-colored berries. These weeds are most dangerous in the spring and summer. That's when there is plenty of sap and urushiol content is high, and the plants are easily bruised. Although poison ivy is usually a summer complaint, cases are sometimes reported in winter, when the sticks may be used for firewood, and the vines for Christmas wreaths. The best way to avoid these toxic plants is to know what they look like in your area and where you work, and to learn to recognize them in all seasons. Among the diseases of man related to his environment, plants of the poison ivy family cause the most universally encountered skin disease in this country poison ivy dermatitis. This family of plants can grow in the great variety of conditions of soil, water, and sun present in all of the states of the continental United States. Common poison ivy (Rhus radicans) can be found in all states but California and Nevada; oak leaf poison ivy grow chiefly in the southeastern part of the country; poison oak is found in California, Oregon, and Washington; and poison sumac grows all along the eastern seaboard and extends to the south into Louisiana and to the north into Minnesota. The plants grow as vines attached to trees, walls, telephone poles, or other vines or along walks, fences, and paths. They also may be seen as ground shrubs, usually small but sometimes large enough to resemble trees. Poison sumac, however, grows only in the form of a woody shrub or a small tree, and as a vine. Both the shape of the plant growth and the shape of the leaves depend on the amount of moisture in the soil and on the quantity and quality of available sunlight. But, with this exception of sumac, the distribution of the leaves never varies only one leaf (comprised of three leaflets) arises from a node on the stem. The leaves, therefore, are never seen in pairs. The leaf of poison sumac consists of 7 to 13 leaflets that are paired (except for the terminal leaflet) along a straight midrib. The nonpoisonous species of sumac all have winged midribs.


The "Poison" and the "Poisoned"

All parts of the plant contain the compounds (catechols) that may produce an eruption of the skin in man. Erroneously called a poison, the material is an allergen, which is a substance capable of inducing allergic reactions after future exposure to that agent. When such an allergic changes occurs from exposure to poison ivy, an inflammation of the skin, called "dermatitis", results at the site of contact with any part of the plant. The first time the skin is exposed to the poison ivy plant chemical, usually no reaction of the skin will be seen. If this or later exposure initiates the allergic state, the dermatitis usually will appear in 7 to 14 days, the time necessary for that contact with the plant to have produced the change in the allergic state and a skin reaction. After such a change in the allergic state takes place, all subsequent significant exposures to the plant will result in dermatitis at the sites of contact within a few hours or up to two to five days later. Some people acquire allergy on the first exposure to the plants, while other acquire it only after many years despite repeated exposures. The oleoresins from poison ivy plants are very potent sensitizers. Many people never seem to become allergic to poison ivy plants. It is quite likely that some people who think themselves to be immune to poison ivy have had minimal, untold reactions, or they may have a low degree of allergy to the plant, and thus have less reaction, or they have little, if any contact with the plant. No person can be certain of being or of remaining insensitive to poison ivy, and all possible precautions should be taken to avoid contact with the plants despite previous evidence of no reactivity. In addition, poison ivy, on occasion, may act as a primary irritant and produce a dermatitis shortly after initial contact in an individual before he becomes sensitized or allergic to the oleoresins of the plants.


The Dermatitis: Who's Sensitive, Who's Not?

Sensitivity to poison ivy is not something we are born with. It develops only after several encounters with the plants, and sometimes over many years. Studies have shown that approximately 85 percent of the population will develop an allergic reaction if exposed to poison ivy. This sensitivity varies from person to person. Although they are not sure why, scientists believe that an individual's sensitivity to poison ivy changes with time and tends to decline with age. The first bout of poison ivy usually occurs in children between the ages of 8 and 16, and can be quite severe. If there is no repeated exposure to poison ivy, or urushiol, sensitivity will probably decrease by half by the time these individuals reach their thirties. Investigators have found that people who reach adulthood without becoming sensitized have only a 50 percent chance of developing an allergy to poison ivy. Those who were once allergic may lose their sensitivity later in life. However, dermatologists say you should not assume that you are one of the few people who are not sensitive-- only 10 to 15 percent of the population is believed to be resistant. That same percentage (25-40 million people) is thought to be very susceptible to poison ivy. These people will develop a rash and extreme swelling on the face, arms and genitals. In such severe cases, treatment by a dermatologist will be required. All poison ivy, and sumac plants cause identical dermatitis consisting of reddening of the skin and blistering. The extent of the dermatitis depends on the areas with which the plants has been in contact, and the severity of the eruption depends on both the amount of plant materials deposited at a particular site and on the degree of allergic sensitivity of the patients. The more allergic plant material left on his kin before washing with mild soap and water, the more likely will an intensely red and severely blistered dermatitis result. Neither the redness nor the blister fluid causes "spread" of the dermatitis. The skin reaction appears to "spread" because of differences in the time of appearance of the lesions. The time required for the lesions to become apparent depends on the amount and duration of the skin's contact with the plant. Areas that have greater contact with the plant, will react earlier than areas of lesser contact, giving the false impression that the later-appearing lesions result from a "spread" of the earlier ones. The blisters may then become infected, and it is the superimposed pustular infection that may spread to other skin sites. Itching almost always accompanies the dermatitis.


Treatment and Prevention

If you think you've had a brush with poison ivy, poison oak or poison sumac, follow this simple procedure: Wash all 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 will neutralize or deactivate the urushiol in the plant's sap and keep it from spreading to other parts of the body. Soap is not necessary, and may even spread the oil. When you return home, wash all clothing outside, with a garden hose, before bringing it into the house, where resin could be transferred to rugs or to furniture. Handle the clothing as little as possible until it is soaked. Since urushiol can remain active for months, it's important to wash all camping, sporting, fishing or hunting gear that may also be carrying the resin. If you do develop a rash, avoid scratching the blisters. Although the fluid in the blisters will not spread the rash, fingernails may carry germs that could cause an infection. Cool showers will help ease the itching and over-the-counter- preparations, like calamine lotion or Burow's solution, will relieve mild rashes. Soaking in a lukewarm bath with an oatmeal or baking soda solution is often recommended to dry oozing blisters and offer some comfort. 0ver-the-counter hydrocortisone creams will not help. What To Do About Poison Ivy? Prevention is the best cure. The best way to avoid the misery of poison ivy is to be on the look-out for the plant whenever you are out-of-doors. Know what you are looking for, and stay away from it. The weeds can be destroyed with herbicides in your own back yard, but this is not a practical solution for forest preserves and other natural areas. If you are going to be in areas where you know poison oak or ivy is likely to grow, wear long pants and long sleeves, and, whenever possible, gloves and boots. Remember that the plant's virtually invisible, oily resin-- urushiol--sticks to almost all surfaces, and can even be carried in the wind if it is burned in a fire. Studies have shown that a sensitive person may develop an internal inflammation from inhaling urushiol. In addition, don't let pets run through wooded areas since urushiol may be carried home on their fur. Removal of the allergen (oleoresin) from the skin with a detergent as soon as possible after exposure will prevent entirely or reduce the severity of an attack of poison ivy dermatitis. Thorough cleansing of the skin under the finger nails should be done, and it is very important to wash the hands so that the poison ivy agents will not be transferred by touching other areas of the body with contaminated fingers. If this washing is delayed more than ten minutes after the initial contact with the plants, then a dermatitis usually will develop in an individual who is sensitive to poison ivy. The application of cold water compresses to the affected areas will afford relief from itching and will reduce the inflammation. Contrary to popular superstition, bathing, showering, and other exposures to water are useful, and even essential, in treatment. Calamine lotion, applied early, will hasten the drying of small blisters. Extensive eruptions are treated by dermatologists with local or systemic corticosteroid remedies, and superimposed infections are treated with antibiotics. Antihistaminic drugs given orally often relieve the itching. For eruptions of the body, where the application of wet dressings may be impractical, tepid baths can relieve discomfort and reduce inflammation. The only satisfactory method for preventing poison ivy dermatitis is avoiding the plants that cause it. There is as yet no perfect skin "protectant" or immunizing technique to improve on the old adage "Leaflets three, let it be".


Common Myths About Poison Ivy

1. Scratching poison ivy blisters will spread the rash. This is not true. The rash is spread by urushiol on the hands--scratching the nose, for instance, or wiping the forehead--before blisters have formed.

2. Poison ivy is "catching." It's not. The rash cannot be passed from person to person-- only urushiol can be spread by contact.

3. Once allergic, always allergic. False. A person's sensitivity changes over time, even from season to season. People who were particularly sensitive to poison ivy as children may not be allergic as adults.

4. "Leaves of three, let them be." This is usually true, but not always.

5. Dead poison ivy plants are no longer toxic. This is not true. Urushiol remains active for up to several years. Never risk handling dead plants.

6. There's no immunization against poison ivy. There is, but it's not recommended-- the procedure is tedious, and carries unwelcome side effects.

7. Hydrocortisone creams will relieve poison ivy itches. They may help with very mild rashes, but, in most cases, these over-the-counter remedies are far too weak to combat the itch of poison ivy.