Most of us have had or will have at least one run in with poison ivy or her itchy cousins. It seems a summertime ritual that is unfortunately all too common. These poisonous plants are very hardy and thrive in many different geographical areas and terrains. In fact, for reasons we will discuss in more detail, they are becoming increasingly prolific and more potent in their ability to inflict telltale rashes than in recent decades. Maybe we can learn a few tips that will help us to enjoy outdoor activities while at the same time avoiding these pesky plants.
What Are Poison Ivy, Oak, and Sumac?
All three of these plants are members of the cashew family Anacardiaceae. They are often collectively called “rhus plants.” Their technical names are as follows:
- Poison Ivy: Rhus radicans or Toxicondendron radicans
- Poison Oak: Rhus diversiloba, or Toxicondendron diversilobum
- Poison Sumac: Rhus vernix or Toxicondendron vernix
The substance that causes skin irritation and rashes is the same in all of these plants. It is an oily resin found in the sap of the plants called urushiol (u-ROO-she-ol). Poison ivy, oak, and sumac abound in almost every part of the U.S. and Lower Canada. In fact, rhus plants are the most common cause of allergic contact dermatitis in the United States. Approximately 60-80% of people are sensitive to the effects of urushiol. The majority of folks will have minimal symptoms at the first exposure, with increasing sensitivity occurring from subsequent contact with the poisonous oil.
What Are the Symptoms of Rhus Plant Poisoning?
Since the signs of inflammation are caused by the same antigen (urushiol) in all three varieties of rhus plants, the symptoms are identical. They generally include:
- Redness of the skin
- Rash, often linear in nature
- Oozing Blisters
Simply touching the plants will not spread the oil. The stem, leaves, fruit, or roots of the plants must be bruised or broken in some way in order for the offending oil to be released. However, rhus plants are very fragile, and even the wind or a person or animal stepping on them can result in the urushiol being released. If your skin is exposed to the sap of the plant, it generally takes some time for it to penetrate the skin and cause symptoms. This length of time varies from person to person based on such factors as skin type and potency of the urushiol, but you usually have a window of time anywhere from 15 minutes to an hour when the poisonous oil can be can be thoroughly washed off with soap and water and avoid contamination or at least minimize its effects. Keep in mind that urushiol can remain allergenic for many months under certain conditions. There have been cases of people who have put away clothing such as a jacket or shoes, only to become infected by coming into contact with the oil the next season after touching the effected item.
Once the urushiol is absorbed into the skin, the hallmark signs of an itchy, blistery rash appear anywhere from 24-36 hours after exposure. Rhus plants do not affect some people at all, but most people will have some reaction that varies in degree depending on how allergic the person is and whether they have been exposed before. In most cases, once you have had an allergic reaction to poison ivy, oak, or sumac, it is easier for it to happen again, and repeated exposures tend to worsen in intensity for many individuals.
There is actually a chemical reaction that takes place that bonds the urushiol to proteins in the cell membranes once it is absorbed into the skin. This bonding has a couple of results. First, once it has occurred, it is impossible to wash the urushiol off the skin at this point. Secondly, the presence of the oil on the cell membranes acts as a red flag that triggers an immunological response. Roaming “T-cells” that fight off antigens such as urushiol and other bacterial and viral invaders are sent to the scene of the crime by the immune system, and this response is what causes the rash and blisters to occur. The symptoms usually last anywhere from 2-3 weeks in most people.
Can the Reactions Be Spread By Scratching?
This is kind of a confusing issue to many people. Let’s see if we can clear it up. Technically the answer is no. Once the skin has erupted in blisters, which often break and ooze fluid, the affliction cannot be spread. There is no urushiol in the watery blisters or rash, so touching or scratching the affected areas will not spread the symptoms to other parts of the body or to other people. However, if you touch an area of your body before the oil has absorbed into the skin and bonded with the cell membranes, you can inadvertently expose other parts of your body to the urushiol. This can be particularly troublesome if you happen to touch sensitive areas such as the face, eyes, or genitals. It is also possible to spread it to other people through direct skin contact. But once the symptoms have begun, it is very unlikely that scratching or touching the area will spread the condition. In more severe cases, new blisters may break out on a different part(s) of the body several days after the initial rashes. However, this is usually not the inflammation spreading, but rather a delayed reaction from the initial exposure that was a less sensitive body part, or came in contact with less of oil.
How Does Most Exposure Occur?
Cases of poison ivy, oak, and sumac are much more likely to happen during the spring and early summer when the new crop of plants is young and tender, and more easily susceptible to bruising. People may be exposed in a number of ways. Direct contact with a bruised plant that has oil on the surface is probably the most common way. Often the rash will exhibit a linear pattern due to being brushed by the plant while walking past it. While most common in the spring and summer, contact with the poisonous urushiol can occur all year round, especially in areas where the winters are mild. Other common ways you can get poison ivy, oak, or sumac are:
- Touching contaminated clothing
- Touching contaminated shoes. Be especially careful when removing clothing and shoes after being in the woods or other areas where rhus plants may be present. Be sure to wash your hands and launder the clothing immediately if you suspect exposure. The bottoms of your shoes are an especially common place for urushiol to be found. Wiping them down with soap and water is always a good idea.
- Using contaminated garden tools. Exposure can even occur the following season if the oil is still present on the tools.
- Contacting the fur of contaminated pets: Many animals such as dogs are not allergic to urushiol themselves, but if you pet them after they have been exposed, the oil can be transferred to you. It can also exist for quite a long time on their fur after exposure. If you suspect you have been in a high-risk area, it might be a good reason to give your pooch a bath.
How Do I Identify Rhus Plants So That I Can Avoid Them?
Unfortunately, these plants can take a myriad of forms, so it is difficult to say specifically what to look for. They also change appearance with the seasons. However, one helpful thing to keep in mind is the old saying: “Leaves of three, let them be.” Below are listed some generalities that can help you identify rhus plants, but the best course of action is to obtain a good field guide with pictures of the various forms.
- Poison Ivy is the most common offender in most parts of the country. But it is rather adept at wearing different disguises. It can appear as a low-lying bush, a plant that stands alone, or a vine. It has three pointed leaflets that are often shiny, especially in the spring and summer, and the middle leaflet has a longer stem than the outside ones. But beyond that, poison ivy can vary greatly in appearance. The leaves may be smooth or “toothed,” and can range in size from less than a half-inch to more then two inches in length. They have a reddish appearance in the early spring, are green in the summer, and change to colors of yellows, oranges, and reds in the autumn, like all deciduous leaves. All forms of the plant have small greenish flowers at the base of the stem, and the vine may have a hairy appearance with clusters of whitish berries, especially later in the growing season.
- Poison Oak is typically found in a low-lying shrub form, but it can rarely appear as a plant or vine. The leaves are found in a three-pronged form like poison ivy, and they are very similar in appearance to the leaves of an oak tree. Beware of anything looking like an oak tree growing close to the ground. As is the case with poison ivy, the leaves and fruit change colors in a similar manner based on the seasons.
- Poison Sumac is usually low-lying as well, but can grow into small trees too. Look for large leaves with smooth edges attached to a reddish stem. The leaves are arranged in pairs directly across from one another, and a typical branch has 9-13 sets. The smooth edged leaves distinguish poison sumac from its other harmless relatives in the sumac family.
Avoiding these plants is the best course of action, but if you have some on your property that you want to remove, they can be carefully pulled out by the roots wearing protective gloves. Do not burn them though. Inhalation of the smoke and burning urushiol can cause inflammation of the respiratory system.
What Treatments Are Available?
Most prescription or over-the-counter remedies contain cortisone, which can have dangerous side effects. The best course of action is usually to let the reaction run its course, and avoid scratching the affected areas with dirty finger nails as this can lead to secondary bacterial infections. Keeping the area cool with compresses or cool baths will help. Some folks find relief from colloidal oatmeal baths as well. Tea tree oil can also be applied to relieve symptoms and speed healing as well. In cases of severe itching, try an antihistamine.
One final thought: Is the incidence of poison ivy, oak, and sumac cases increasing, and if so why? Many researchers believe that due to several environmental factors, more rhus plants are growing, and they are becoming more potent as well. The primary causes that are likely responsible, at least theoretically, for this phenomenon are global warming that results in more carbon dioxide in the atmosphere, and the excessive clearing of land that gives rhus plants, and other types of vegetation as well, more exposure to sunlight and water. Whatever the case, the best way to eliminate the negative effects of poison ivy, oak, and sumac are to learn how to identify them, avoid them if possible, and take appropriate precautionary measures if you suspect exposure. Other than that, don’t let these poisonous plants cramp your style when it comes to enjoying the Great Outdoors.