Poison Ivy Dermatitis

"leaves of three, let it be"

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Revised 6/25/99

Charles Booras M.D.

by Charles H. Booras, MD



Summer is here and it's 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 in the Toxicodendron species family that cause the same itchy red rash. They are...

To see some pictures...
click on the plant name

See also jewelweed (used for on-the-trail treatment)

Together, they produce more cases of "allergic contact dermatitis" than all other allergens combined.

Poison Ivy is by far the most common cause of this allergic skin reaction. The entire plant, except the pollen, is toxic throughout the year, even during the winter months when the branches and stems are leafless.

Contact dermatitis simply means that something has been applied to the skin which has caused the skin to react to it. An initial exposure is necessary to "sensitize" the patient; In other words, you get "one free pass". A subsequent exposure will result in an allergic reaction if the plant oil remains in contact with the skin for as little as 10 to 15 miniutes. The resulting rash begins after a 12 to 48 hour delay and persists for about two weeks up to four weeks or longer.

The resulting rash can range from mildly unpleasant to a true emergency with intense swelling, blistering, and oozing. With even a moderate case the itching can seem unbearable.

The Culprit:

All of these plants contain an oily resin called Urushiol ("you-ROO-shee-ol") which causes the rash. Urushiol has as its dermatitis-producing principle, pentadecylacatechol. This chemical does not evaporate and dries quickly on clothing, shoes, animals and tools.

Urushiol remains potent for a year or longer. Therefore, it is important to wash any tools, shoes or clothing after exposure to poison ivy. The resin will remain active on these articles and can cause a rash months, or even years, later. Removal of the oil with an effective cleanser, such as Tecnu® is helpful to avoid contaminating unsuspecting victims in the future.

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 resin but they can still get it. Children become susceptible by age 3 and are highly susceptible by age 12. You can develop the reaction at any time during your life. Sensitivity is just a matter of being exposed enough times until the body becomes allergic to the Urushiol.

Those who are exposed usually pick up the resin on their legs and palms and then transfer it to other areas, often their face and genitals. It only takes about 15 minutes for the resin to begin to bind with the keratin (top) layer of the skin, which then sets the inflammatory process into motion. It is noteworthy that a rash rarely breaks out on the palms, since the keratin layer of the skin is often too thick for the resin to bind there.

The best thing to do if you know you've been exposed to poison ivy / oak / sumac is to wash your skin immediately with rubbing alcohol (or Tecnu®), in which the resin is soluble. Beer or other beverages containing alcohol will help to dissolve the resin if rubbing alcohol is not available. Soap works, but not as well. If the oil has been on the skin for less than six hours, a thorough cleansing with strong soap, repeated three times, may lessen or even prevent a reaction.

If you do wash with soap, make sure you do it in the shower so the resin is washed down the drain, not deposited in a slick on the sides of the tub to spread to others. If you can wash the area with plain cold water within a few hours of being exposed you may be able to remove a lot of the urushiol. Use a LOT of COLD water. Be aware that the water is simply spreading the oil around; the idea is to use enough water to wash all of the oil from your body.

Do not use hot water which can open your pores to the oil.

The resin is absorbed quickly into the skin. If the oil is on your skin for as little as ten to fifteen minutes, it can lead to an allergic reaction. The eruption is characterized by redness, papules (bumps), vesicles (blisters) and linear ("in a line") streaking. Mild cases can last 5 to 12 days. More severe cases can last up to 30 days or longer.

The eruption usually appears within two or three days but may occur within eight hours. The eruption rarely is delayed longer than ten days.

Once the rash appears, the original oil has all bonded to the victim's skin, so it can't be spread to others.

Contrary to popular belief, the fluid in the vesicles or blisters is not allergic and will not spread the rash. The blisters are the body's natural allergic reaction to poison oak and poison ivy. If the blisters break and ooze, the fluid does not contain the oils that cause spreading. The rash will frequently break out in stages and continue spreading for the first 1 or 2 days.

If new areas of rash appear after 3 days, you are probably getting re-exposed to the plant oils, most likely from contaminated clothing, tools, or even your cat or dog (their fur protects them but can harbor the oil for a prolonged period of time). As mentioned above, the resin will remain on any exposed (but uncleaned) objects such as clothing or equipment. If you put on your exposed shoes a week later, you can wipe the resin from your shoes onto your face or other areas.

Interestingly, the urushiol can be vaporized when exposed to a fire. If you have a neighbor who is burning poison ivy, the resin will rise with the smoke. If you are downwind when the resin cools off and rains back down to earth, you could receive a coat of urushiol on any uncovered areas resulting in a surprise case of poison ivy.

Under no circumstances should you burn the plant; the smoke is as potent as the plant itself. Inhaling the smoke can produce a systemic reaction, including potentially serious, and life-threatening, lung inflammation.


Most of the treatments are aimed at reducing the itching until the self-limited rash runs its course, which takes about two weeks. Since easing the itching is the important result, trial and error works very well. If one of these suggestions seems to work, by all means, stick with it. If it's not working or seems to worsen things….please stop.


  • Compresses.

Most people find that cool compresses in one form or another are quite soothing. Try using a towel or wash cloth soaked in either plain tap water, Epson salt water (up to about 2 tablespoons of salt per cup, stir until the salt dissolves) or Burow's Solution (an astringent solution -- you can make it yourself using Domeboro tablets or powder--available over-the-counter). This can help relieve the intense itching and remove any dry crust that has formed as a result of the rash. Let the water dry on the area, leaving a salt dust covering. Do this a couple of times a day (or more).

A fan blowing over the cool compress will diminish some of the heat of the itching and help to dry up some of the ooze coming from the rash. As the skin is cooling, the blood vessels compress and that cuts down on the itching and the new ooze. This is especially good during the two or three worst days of the rash. Along the same lines, some dermatologists recommend rubbing an ice cube gently over the rash several times a day, then letting the skin air dry. Soaking in a tub, particularly using an oatmeal bath such as Aveeno®, can also be very soothing to the itch. Be sure the bath is cool or lukewarm -- but not hot -- as heat tends to make the rash even more inflamed. (I'm aware that some people maintain that a VERY hot shower can dull the pain and relieve some itching. I, personally, do not recommend heat therapy for Poison Ivy).

  • Topicals

After cooling your skin (using any of the forms mentioned above) coat the rash with a lotion such as Calamine®. This continues to help relieve the itching and dry up the blisters. Be sure to check the expiration date on an old calamine bottle in your medicine cabinet, since it may not be effective after the expiration date. Calamine may not seem to do much, in some cases, but I don't think it will hurt anything and is worth a try in the early stages.

Be sure the lotion does not contain benzocaine, zirconium, or a topical antihistamine, such as Benadryl® (which is in Caladryl®). These can actually make the rash worse by producing their own allergic reactions when applied to already sensitive skin.

Smearing on 1% hydrocortisone cream (available over-the-counter without prescription) may give some relief, but is nowhere nearly as effective as the potent topical corticosteroid preparations available from your physician by prescription. These can help suppress the itching and give temporary relief, but do little to hasten the drying up of the rash.

Special Note: For on-the-trail treatment and prevention you can't beat nature's own remedy, jewelweed. The Native Americans used Jewelweed. It is usually found in moist, shaded areas and is identified by it's waxy leaves. After a rain or heavy dew, water beads up on the waxy leaves and looks like jewels. It's almost always found close to ivy, so it's usually availible when you need it. Crush a few leaves and stems and rub them on your skin, or crush and soak in water for a larger amount. You can also put a mess of jewelweed in a large glass container and make a "sun tea" out of it to use as a compress (not to be taken internally) to help soothe the eruption if it develops.

  • Antihistamines

Benadryl® is available over-the-counter without prescription and can help with the itching. Taking Benadryl® at nighttime will make most people drowsy and help them sleep through the night without itching. Again, don't use Benadryl® cream or spray topically, because this can cause its own reaction. Several other antihistamines (Atarax® , Periactin® , etc.) are available by prescription when you see your doctor and may be more effective than over-the-counter products.

  • Steroids

In moderate to severe cases of poison ivy, poison oak, or poison sumac it is a good idea to see your doctor. Sometimes an oral corticosteroid such as prednisone may be useful.

These are not the steroids abused by some body-builders. This class of corticosteroids is produced by your own body and plays an important role in reducing inflammation.

Systemic steroids produce rapid resolution of both the itching and the rash. If they are needed, a gradually tapering dosage over about 12 days should be given. There are "Dose packs" available by prescription which make the dosing regimen a bit easier to follow. When taking steroids, I personally recommend taking the entire days dose in the morning after a meal. This is more convenient than dividing the dose during the day and is similar to our bodies circadian rhythm of secreting more natural steroid in the morning. Check with your personal physician if a steroid has been prescribed for treatment.

The dosage needs to be tapered in order to avoid side effects after discontinuing use. The entire 12 day course should be taken since stopping too early may result in a rebound rash nearly as bad as the original. Some physicians prefer to use an injectable steroid instead of one taken by mouth.

Warning: Some homeopathic treatments for Poison Ivy utilize extracts from these plants which are taken by mouth. The ingestion of Toxicodendron from this family of plants, or herbal remedies that contain it, can produce a life threatening gastroenteritis and, in my opinion, should be avoided.


  • The best prevention for allergic contact dermatitis is complete avoidance of the plants. Individuals should learn to recognize and avoid poison ivy. Gloves, long-sleeved shirts and long pants are advisable when working around poison ivy.
  • If exposed, wipe the affected area as quickly as possible with alcohol or an alcohol-containing beverage. Some people even carry a container of rubbing alcohol with them to wipe off their skin whenever they run the risk of exposure to the plants. As above, washing with soap and cold water as soon as possible can be helpful.
  • Using barrier creams (such as Ivy Shield, Hollister Moisture Barrier, IvyBlock, Stokogard Outdoor Cream, or Hydrophil) may help protect against contracting the rash.

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