Poison Ivy, Oak, and Sumac: A-to-Z Guide from Diagnosis to Treatment to Prevention

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Poison Ivy, Oak, and Sumac: A-to-Z Guide from Diagnosis to Treatment to Prevention

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It’s Monday morning. You’ve had a wonderful weekend playing with your kids and your dog, romping through the woods. Now, as you lie in bed, you hear whimpering coming from the next room. A few minutes later, your son comes in to join you in bed, sporting red itchy patches on his arms and legs. He has poison oak (or poison ivy, or poison sumac).

What is poison ivy, oak, and sumac?

Poison ivy, poison oak, and poison sumac together produce more cases of allergic contact dermatitis than all other allergens combined. The resulting rash can be anything from mildly unpleasant to a true emergency with intense swelling, blistering, and oozing. With even a moderate case, as you may have experienced, the itching can seem unbearable.

Whichever of these plants he came across while playing, the culprit is the same — an oil called urushiol. This oil is found in the leaves, roots, and twigs of these plants. There is no difference in the rashes, since there is no difference in the cause. A few other plants contain the same oil in lesser amounts, including the Japanese lacquer tree (and thus some lacquered furniture), the gingko tree, the shells of cashews, the shells of brazil nuts, and the rinds of mangoes. Extra sensitive individuals would do well to avoid all of these.

Who gets poison ivy, oak, and sumac?

Most people will have no reaction the first time they are exposed. In fact, children under the age of 7 are rarely sensitive. Sensitivity is particularly rare under the age of one, and when infants do break out, the rash is usually mild. As many as 15 –30 percent of individuals never develop sensitivity.

The rash is most common in the summer, but it can occur at any time of the year.

What are the symptoms of poison ivy, oak, and sumac?

Wherever the oil touches the skin of a sensitive individual, an exquisitely itchy, red rash will appear between 8 and 72 hours (usually 12-48 hours) later, which will often go on to develop blisters. The first time a person touches this oil, s/he may break out 7 to 10 days later. The rash usually looks like lines, streaks or patches where the oil came in contact with the skin (Healthy Children, AAP June 2010).

Is poison ivy, oak, and sumac contagious?

The oil from poison plants can stick to virtually anything. It can dry and remain potent indefinitely. This is why camping trips can produce such horrible cases of poison oak. Anything that your child has touched between his exposure and a thorough shower should be washed in soap and water (preferably hot), hosed down, or soaked in water and alcohol. This includes clothing, shoes, balls, toys, tools, and the towel he used after his shower. After washing the contaminated articles, don’t forget to wash your own hands, and anything those articles touched.

Once the oil has been removed, the rash from poison oak or poison ivy is not contagious. Even the oozing blisters are not contagious, although they look like they should be. Because new blisters can keep appearing over the course of a week, people assume that touching the rash causes it to spread, or that the ooze itself is responsible for the spreading. The fluid that fills the blisters is one’s own serum, not the poisonous oil. The skin only breaks out where it actually is exposed to the urushiol. The sensitivity of the skin, and the amount of oil, determine the speed of the eruption. Places where the oil is most concentrated, or the skin the most vulnerable, break out first, followed days later by places where there was only a little oil, or the skin is a more effective barrier. Woe to those with eczema!

As long as the oil is no longer present, scratching does not make the rash spread. Scratching does make the already intense itching even more unbearable and can cause the rash to get infected. Some doctors recommend cutting your child’s fingernails short to prevent scratching and infection.

How long does poison ivy, oak, and sumac last?

The rash usually lasts about two weeks.


The diagnosis is based on the history and the physical exam.


Most people find that cool compresses in one form or another are quite soothing. Try using a towel or washcloth soaked in either plain tap water or Burow’s Solution (an astringent solution — you can make it yourself using Domeboro tablets or powder packets. A fan blowing over the cool compress can help. As the skin is cooling, the blood vessels constrict, cutting 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, especially using an oatmeal bath such as Aveeno, can also be very soothing. Be sure the bath is cool or lukewarm — but not hot — as heat tends to make the rash even more inflamed.

After the cooling, coat the rash with a shake lotion such as calamine. This continues to relieve the itching and helps to 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.

Smearing on hydrocortisone, or other topical corticosteroids, will help suppress the itching a bit and give temporary relief, but does little to hasten the drying up of the rash.

Taking an oral antihistamine can help with the itching quite a bit, although it does not speed up resolution of the rash. 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 skin reaction.

The goal of reducing itching is brought about by cooling (by restricting the blood vessels), by drying the rash, or by quieting down the allergic response.

In severe cases of poison ivy, poison oak, or poison sumac, it is a good idea to see a doctor. Sometimes large blisters need to be drained and sometimes an oral steroid such as prednisone may be useful. 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. The dosage needs to be tapered to avoid side effects after discontinuing use, and the entire course should be taken since stopping earlier may result in a rebound rash as bad as the original.


The best way to prevent an outbreak of poison oak is to avoid any contact with the oil in the first place. Teach your children to recognize the poisonous plants of your region. Poison ivy has three leaves that grow on a single red stem. The leaves turn bright red in the summer. The plant grows in all areas of the U.S. except the Southwest. Poison oak is a shrub and is found on the West Coast of the U.S. Poison sumac is also a shrub that typically grows in swampy areas around the Mississippi River area of the U.S. and has 7-13 leaves arranged in pairs along it’s stem (Healthy Children, AAP June 2010).

Before an outing to an area where you are concerned that these plants may be lurking, you might want to coat your child’s skin with a barrier cream. Hollister Moisture Barrier, Hydropil, IvyBlock and Stoko-Gard Outdoor Cream are all fairly good at protecting the skin from the oil, but must be reapplied hourly to remain effective.

Again, the oil is the culprit. As soon as you suspect that your child is exposed to urushiol, have him wash thoroughly with lots of warm water and soap. (Hot water opens the pores, and may transiently increase exposure.) Water alone will also work, but not quite as well. If you don’t have water, use rubbing alcohol. Don’t use a washcloth, since this tends to spread the oil to other patches of skin. Likewise, a shower is much preferable to a bath. Have him rinse thoroughly. If the oil is removed within 5-10 minutes, you may prevent, or at least minimize, the rash. Even if he doesn’t wash for a long time, washing is still very important. The oil remains on the skin until it is rubbed or washed off. It can cause a new reaction wherever it touches — thus, after the forearms and lower legs, the most common spot for a poison ivy rash is the male genitalia!

Perhaps in your weekend outing you were exceptionally careful. You and the kids stayed on the path, and you saw no poison oak or ivy — but your dog went chasing after a bird. When he rejoined you, his fur was coated with oil. The oil transferred easily when he rubbed against your son’s clothing, or when you leaned down to pet him. Thus, the last tip for prevention — don’t forget to hose down the dog!


Last medical review on: July 30, 2019
About the Author
Photo of Alan Greene MD
Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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