Poison Oak, Poison Ivy and Poison Sumac

Craig Kraffert, MD

Poison oak, poison ivy and poison sumac are the main causes of allergic skin rashes in North America. Of these, poison oak and poison ivy are most common with oak being prevalent in western North America and ivy being prevalent in the east. These plants belong to the genus Toxicodendron. The name is fitting as it describes two distinctive attributes of these plants. Toxic refers to the fact that significant contact with these plants often causes severe symptoms and dendron refers to the tentacle-like nature of the branches that seem designed to promote contact with all who come too close. All parts of these plants - leaves, branches, berries and roots - contain toxic resinous oil called urushiol (you-ROO-shee-ol) that is responsible for the plants’ allergic properties.

Although sensitivity may vary over a person’s lifetime, it is estimated that between 75 to 95 percent of people exposed to urushiol will have an allergy to it at some point. Most people remain allergic to these plants for their entire lives. If there is ever a doubt as to the presence or absence of allergy to these plants, it is always best to assume allergy exists.

For many people, the first realization that they might have come in contact with one of these poisonous plants occurs when the rash develops or when they consult with a medical professional about a rash. The rashes caused by poison oak vary greatly in their appearance depending upon a number of factors including the way in which the contact occurred, the extent and areas of contact, and the individual’s sensitivity to urushiol.

Symptoms of Poison Oak Rash

Certain features of the rash are relatively consistent. Streaks of a red and often blistered itchy rash on exposed skin surfaces are the hallmark of these rashes. Streaks occur because the plant’s branches or leaves brush past the skin as people travel near them. Also, scratching the skin before the resin is removed can spread the resin in a streaked way.

In addition to this typical presentation of poison oak, many other appearances may occur including facial or eyelid swelling or larger continuous areas of rash. Areas with the greatest urushiol resin contact tend to erupt first. The rash may begin immediately after contact or may be delayed in onset by a week or more. Areas with less exposure erupt later, but the overall development of the rash usually occurs within a three-day span from start to finish.

Poison Oak is Not Contagious

If the urushiol is not removed from pets or objects such as clothing, there may be repeated contact with urushiol resulting in ongoing development of the rash beyond three days. This pattern may be confusing to some and has led to the widespread false belief that these rashes are contagious. The rashes are caused only by contact with urushiol and are in no way contagious. Blister fluid from these rashes is not capable of spreading the rash. Once the resin is removed from the skin by washing and removing resin-coated clothing, the ability to spread the rash ends. Most people with repeated contact with poison oak and poison ivy begin to recognize the various features of these rashes.

Prevention and Treatment of Poison Oak

Treatment of poison oak consists of avoiding contact with the plant’s urushiol resin, protecting oneself from the consequences of contact with the urushiol and treating the symptoms of the rashes caused by contact. In order to avoid contact with these plants, it is important to know what they look like. Their appearance changes through the seasons but they remain toxic year round. A key identifying feature of these plants during leaf-bearing seasons is that the leaves invariably come in triplets, thus the phrase “Leaves of three, let it be.” The leaves of three rule does not apply to poison sumac.

In the west, cases of poison oak are common in late fall and winter when the plants have no identifying leaves. Still, they contain ample urushiol in their tentacle like branches. It is important to study the winter appearance of these plants in order to avoid them year round. Dead plants retain the ability to cause rashes for four years or longer. Rashes from these plants can also develop as a result of breathing smoke from burning them and from secondary contact with urushiol, typically from pets that have had plant contact. It is important to stay far away from any smoke generated from burning these plants. The smoke can cause toxic symptoms in the lungs and internally as well as contribute to a widespread skin rash. Pets must not be allowed to roam in areas where these plants may reside.

There are certain occupations and leisure activities in which contact with these plants can not be totally avoided. In these instances, long pants, long sleeves, boots and gloves are recommended. Additionally, products such as Ivy Block are designed to block the resin from spreading through the skin and causing the rash despite skin contact. These should be applied to any skin areas that might potentially be exposed to urushiol.

If one is aware that there may have been recent exposure to these plants, all possibly contaminated skin areas should be washed with cool water. Bleach does not remove urushiol, but a skin cleansing product, Tecnu®, does and should be used if available as it neutralizes the resin and reduces the risk of skin rash. Tecnu also removes urushiol from pets, clothing and tools. Once a pet, clothing or other object becomes contaminated with urushiol, it may remain a source of skin rash for a year or longer if the urushiol is not removed by washing.

Treatment of poison oak and ivy rashes consists of controlling the symptoms until the allergic reaction fades. These rashes can last from one to four weeks on average depending upon the extent of contact and other factors. The treatment of poison oak or poison ivy depends upon the severity of the symptoms. Milder cases can be treated with over the counter remedies such as oral Benadryl®, hydrocortisone products and soothing applications. More severe cases require medical attention. Scratching should be minimized to reduce the risk of open sores and possible infection.

If poison oak or ivy is caught from burning the plants and lung involvement is suspected, a physician should be consulted. Similarly, if there is any indication of infection or if symptoms are severe or extensive, a physician should be called. More severe cases may require prescription treatment such as strong cortisone cream, strong antihistamines, antibiotics if infection is present, and, in the worst cases, internal cortisone pills or shots.

When it comes to poison oak, ivy and sumac, there is no substitute for staying away from the plants. For people in many areas of the North America, however, this is simply not possible due the prevalence of these plants in certain regions. It is important to know how to minimize the chance of developing the allergic rash as well as how to treat it and when to consult with a physician.