Washington Publishers

The Health Gazette

Click here to visit our Parenting Forum

Poison Ivy

Summer is here and it is time to spend some quality time outside. Whether you are hiking or working in your garden, you are always at risk for getting poison ivy. There are three types of plants that cause the same itchy red rash. They are poison ivy, poison oak and poison sumac. They are called the poison rhus plants. Poison oak is more prominent on the West Coast whereas poison ivy occurs throughout the United States. Poison ivy is by far the most common cause of the allergic skin reaction. The poison ivy plants are related to the Japanese lacquer and cashew tree nut trees, the mango, and the marking nut tree of India. Exposure to products containing any of these substances can produce a reaction identical to poison ivy.

Occupational exposure causes much disability every year in the United States. Although allergic contact dermatitis can occur in any setting, many cases are related to exposures in the workplace. When all occupationally related illness in the United States was last estimated, allergic contact dermatitis accounted for 7%, at an annual cost of $250 million in lost productivity, medical care, and disability payments.

The spring and summer are the most common times of the year for poison ivy and oak. Poison ivy and oak have three leaves on each stem and grow as a vine or bush. Although poison ivy and poison oak usually have three leaves, additional leaves are not unusual in western oak. Sumac has two rows of leaves opposite each other and one leaf at the end of the stem. It grows as a bush or tree. The leaves of all three plants are shiny and coated with an oily chemical, which causes the allergic reaction. The oils are also in the stems, vines and roots of these plants. Poison ivy is produced by an allergic reaction to the oil. The medical term is allergic contact dermatitis. It is unlike the skin reaction that occurs on exposure to an acid or other irritant. This is called irritant contact dermatitis and the reaction occurs almost immediately after exposure. Allergic contact dermatitis is a form of delayed hypersensitivity mediated by lymphocytes (white blood cells) sensitized by the contact of the resin to the skin. In other words, the body’s immune system recognizes the resin and releases chemical mediators that cause the outbreak on the skin. Allergic contact dermatitis is less common than irritant contact dermatitis. The allergic hypersensitivity reaction is dependent upon immunologic changes induced by a previous contact with the same plant or a closely related species. In other words, repeated exposure to the plant usually results in an increasingly more severe reaction. The first exposure to poison ivy will not result in a reaction or rash but the body develops an immune response that will become increasingly more severe with subsequent exposures.

Pets can get the resin on their furry coats and spread the resin to humans. Keep in mine that gloves, shovels or other garden tools that have the resin on them can cause poison ivy if you re-expose yourself even several months after you last used them.

A particularly severe case of poison ivy can occurs when you are burning debris that contains poison ivy plants. The fire produces resin-containing smoke that can be inhaled and deposited on the exposed parts of the skin. The resulting rash can cause a severe reaction that may need more potent medication like a steroid shot or oral prednisone.

Clinical evidence shows that no person is completely immune to the resin. Some are sensitive to small amounts, whereas others react only to large amounts. Severe cases of poison ivy have occurred after supposedly immune individuals have purposely rubbed poison ivy leaves onto their skin.

When I was a child, I remember hearing that if you eat a poison ivy sandwich, you will never get poison ivy again. Fortunately, I never did try this. I can assure you that this is just an old wives tail. Although I have never known anyone to attempt this, I suspect the reaction would be quite severe and possibly even fatal.


All of these plants contain the same oily chemical that causes the rash. It is an allergic contact dermatitis. The chemical is a resin called urushiol. This chemical is nonvolatile and dries quickly on clothing, shoes, animals and tools. Urushiol can remain potent for months in very dry conditions. When conditions are humid and warm, the resin may only be potent for a week or two. Therefore, it is important to wash any tools, shoes or clothing after exposure to poison ivy.

When your skin comes in contact with any part of the plant, it is only a matter of time before you breakout with a rash, assuming you are allergic to it. Not everyone is sensitive to poison ivy. It has been estimated that 70 percent of the population is susceptible to poison ivy. Dark-skinned individuals seem less susceptible than others. Elderly individuals and infants are not as susceptible to the plant but they can still develop a reaction. Children become susceptible by age 3 and are highly susceptible by age 12. Repeated exposure can result in sensitization in infants, dark-skinned individuals and elderly people thus making then susceptible to poison ivy. More than likely, anyone can develop a sensitivity to poison ivy. If you know you have been exposed to poison ivy, it is important to wash off immediately. The resin is absorbed quickly into the skin. As little as ten minutes of exposure may produce the allergic reaction.


The eruption usually appears within two days but may occur within eight hours. The eruption occasionally can be delayed as long as ten days. Washing off with soap and water immediately after exposure will limit the severity of the reaction. The resin is absorbed into the skin so you will still breakout with a rash depending on your sensitivity to poison ivy. The longer you wait to wash off the resin, the worse the reaction will be. The reaction is more severe if the skin is thin such as on the face or neck. The palms and soles have very thick skin so they are not as susceptible. The length of exposure and the amount of resin on the skin also determine how severe the reaction will be. Contrary to popular belief, the fluid in the vesicles or blisters will not spread the rash. This fluid is totally harmless and in no way can spread the rash or make it worse. It is easy to see how this misconception got started. The rash will frequently breakout in stages depending on the length of exposure and the amount of urushiol on the skin. If the face is exposed heavily and for a long period of time, then you may breakout within 24 hours. If your arms are exposed for one hour, then you may not breakout for 48 hours. If your legs are only exposed for ten minutes, then you may not breakout for a week. Obviously, it appears as if the rash is spreading over the body. Another factor to consider is the possibility of re-exposure. As mentioned above, the resin will remain on exposed objects. If you put on your contaminated shoes a week later, you can wipe the resin from your shoes to your face or other areas. One of the most severe reactions that I have seen, occurred when a patient was downwind of a neighbor who was burning poison ivy. The urushiol can be vaporized when exposed to a fire. The unfortunate individual, who is downwind, could receive a coat of urushiol on any uncovered areas resulting in a surprise case of poison ivy. Inhalation can produce a potentially fatal reaction.

The symptoms are as follows:

1. A red streaky rash indicates where the resin has contacted the skin.

2. A patch of vesicles (water blisters).

3. Intense itching.

4. Swelling of the skin, which is particularly severe on the face.

5. Swelling of the throat can occur particularly if smoke from the burning plant is inhaled.

6. Fever, nausea and chills may develop in severe cases.

7. The open lesions are very susceptible to a secondary bacterial infection from staphylococcus or streptococcus (impetigo).


Treatment will depend on how severe the reaction is. For minor cases it may only be necessary to apply an over the counter hydrocortisone cream and some Calamine lotion. As soon as possible after exposure, wash all exposed skin with soap and water to remove the plant resin. Apply a cloth soaked in Domeboro solution for relief of the itching. It should be used for 15 to 30 minutes several times a day for 1 to 3 days until blistering and severe itching is controlled. Topical steroids do not penetrate through blisters. Calamine lotion or ointment can be used to reduce the redness, ease the itching, and help dry up the blisters. Take a lukewarm baths with cornstarch (1/2 cup) or oatmeal added to ease the itching.

For more severe reactions such as fever, headache, eyes swollen shut or drainage from the sores, you should see your physician. It may be necessary to take an oral steroid such as prednisone.

Occasionally, it is necessary to administer a steroid shot. Prednisone is usually prescribed as a dose of 20 mg twice a day for ten days, then once a day for ten days. I have found that a 20-day course seems to work the best. With shorter courses the rash will almost completely resolve, but after the prednisone is finished, the rash may return. Benadryl capsules are over the counter and can help control the itching. Atarax and Periactin are also excellent, but they require a prescription. Domeboro solution can be very soothing and decrease the itching. It is particularly helpful the first two or three days. Calamine lotion relieves the itch. Avoid using topical preparations that contain benzocaine, zirconium, or antihistamines (Benadryl). These substances will frequently cause an allergic skin reaction, which may worsen the poison ivy. If a secondary bacterial infection (impetigo) occurs, you will need to take an oral antibiotic. Impetigo is a crusty yellow sore that spreads rapidly to other parts of the body and doesn’t seem to heal like the other areas of poison ivy.


The best prophylaxis for allergic contact dermatitis is complete avoidance of the plants. Individuals should learn to recognize and avoid poison ivy. Unfortunately, barrier creams or other solutions are of no value in preventing poison ivy. Long-sleeved shirts and long pants are advisable when working around poison ivy. Rubber gloves are not protective because urushiol penetrates the rubber. Use heavy-duty vinyl gloves instead.

Occasionally, people cannot avoid poison ivy because of the nature of their job. Some allergists will attempt to desensitize a patient to poison ivy. Unfortunately, this is not very effective. Complete desensitization cannot be accomplished. The FDA has removed from the market poison ivy resin in capsules and injectable syringes for hyposensitization.

It is of course possible to destroy and remove the poison ivy but this may require weeding on several occasions because the plants tend to regrow because some of the root system was left behind. You should be very careful if you are sensitive to the ivy. Cover as much of your body as possible and wash your clothes after use. The dead ivy plants are capable of producing a reaction since they still have the resin covering them. Burning the ivy can be very hazardous as mentioned above.

There are several products on the market that kill plants by spraying them with a solution. This can be very effective and conveys less risk of exposure to the ivy.


1. Fisher A., Poison Sumac (Anacardiaceae) Rhus Family. Contact Dermatitis 3rd ed. pp. 405-417, 1986.

2. Belsito, DV, The diagnostic evaluation, treatment, and prevention of allergic contact dermatitis in the new millennium, J Allergy Clin Immunol March 2000;105:409-20.

3. Association of Schools of Public Health and National Institutes for Occupational Safety and Health. Proposed national strategy for the prevention of leading work-related diseases and injuries, 2. Washington (DC): The Association; 1988. p 65-95.

The information provided above is offered as a community service about health-care issues and is not a substitute for individual consultation. Advice on individual problems should be obtained from your personal physician. This information is based on research by the author and represents his interpretation of the literature.

Poison Ivy
Poison Ivy
Poison Sumac
Poison Sumac
Poison Oak
Poison Oak

* * *

Readers may send questions to our email address. This column is for informational purposes only and is not a substitute for professional or medical advice.

* * *

This web page is best viewed in 1024 x 768 resolution. Last updated April 2009. Over 1,194,000 page views.
This web site is maintained by Washington Publishers, Tallahassee Florida, USA, and uses Sun Domains and Software.
To have objectionable or potentially copyrighted material evaluated for removal on this site, click here.
Copyright © 2000 - 2009 All Rights Reserved Washington Publishers
Washington Publishers is not an affiliate of Inside Washington Publishers.
Learn more about our current privacy and information practices.