Poison Ivy, Oak, and Sumac

Poison ivy, poison oak, and poison sumac (belonging to the Anacardiaceae family) are plants that can cause a rash if individuals come in contact with the oily resin found in them.

Poison Ivy

Picture of poison ivy

Poison ivy (Toxicodendron radicans -- eastern poison ivy/Toxicodendron rydbergii -- western poison ivy) typically grows as a vine or shrub, and it can be found throughout much of North America (except in the desert, Alaska, and Hawaii). It grows in open fields, wooded areas, on the roadside, and along riverbanks. It can also be found in urban areas, such as parks or backyards. Poison ivy plants typically have leaf arrangements that are clustered in groups of three leaflets (trifoliate), though this can vary. The color and shape of the leaves may also vary depending on the exact species, the local environment, and the time of year. The plant may have yellow or green flowers, and white to green-yellow berries, depending on the season. Eastern poison ivy typically grows as a hairy ropelike vine, whereas western poison ivy tends to grow as a low shrub.

Poison Oak

Picture of poison oak

Poison oak (Toxicodendron diversilobum) grows as a vine or shrub, and it is found in the western United States and British Columbia. It also has a leaf arrangement similar to poison ivy, with clusters of three leaflets. The leaves may sometimes resemble true oak leaves.

Poison Sumac

Picture of poison sumac

Poison sumac (Toxicodendron vernix) grows as a shrub or small tree, and it is found in the eastern/southeastern United States. It grows in very wet areas, and it can be found along the banks of the Mississippi River. Each stem contains seven to 13 leaves arranged in pairs. It has the potential to cause a more severe rash than either poison ivy or poison oak.

Exposure to all of these plants can produce a rash, which is caused by sensitivity to an oily resin found in these plants called urushiol. This substance can be found on the leaves, stems, flowers, and roots of these plants. Interestingly, it can remain active even after the plant has died.

• Exposure to even very small amounts of urushiol amounts less than a grain of table salt will lead to the development of a rash in 80%-90% of individuals.

The rash (an allergic contact dermatitis) can be caused by direct contact with urushiol by touching the plants or by indirect contact with the plant oil that may have contaminated a pet's fur, tools, clothing, or other surfaces. Airborne contact is also possible if these plants are burned and the urushiol particles land on the skin, and it can affect the lungs as well if the urushiol is inhaled.

• In the United States, Toxicodendron dermatitis is the most common cause of contact dermatitis.

Sensitivity to urushiol occurs when individuals come into contact with it. The first time a person is exposed, they may not develop a rash. However, with repeated exposure, sensitivity develops which ultimately leads to the development of the characteristic rash.

• Most people (about 85%) will develop sensitivity, while a small percentage of individuals (about 15%) never develop an allergic reaction to urushiol.

Any individual who comes into contact with these plants is at risk of developing the rash. However, people who spend more time outdoors in geographic areas where these plants are known to grow are at higher risk.

• This may include certain occupations associated with outdoor work in these areas, such as gardeners, groundskeepers, farmers, forestry workers, and construction workers.
• Hiking enthusiasts may also be at higher risk if they venture into areas where these plants are present.

Picture of a poison oak rash; SOURCE: CDC

Susceptible people will develop the characteristic rash after exposure to the urushiol from these plants, typically within 12-72 hours after the initial contact. The signs and symptoms can include the following:

• Redness of the skin
• Swelling of the skin
• Itching of the skin
• An outbreak of small or large blisters

The rash may appear bumpy, streaky, linear, or patchy, and it will affect the areas that have come into contact with the oil resin. Areas that have been exposed to a larger amount of urushiol may develop the rash more quickly, and the rash may appear more severe. In some instances, new lesions may continue to appear for up to two to three weeks. One can spread the rash to other parts of the body if one's contaminated hands (with the oil resin) touch other areas. The fluid that sometimes oozes from the blisters does not contain urushiol and therefore does not spread the rash, and other individuals who touch this fluid will not develop the rash. To spread the rash to someone else, they must directly come into contact with the oil resin. Generally speaking, the rash slowly improves and disappears after one to three weeks in most individuals.

Overall, the symptoms may range from mild to severe. Rarely, in extreme cases, an anaphylactic reaction can develop.

If these plants are burned, the airborne particles of urushiol can be inhaled, causing respiratory difficulty from irritation of the lungs. Occasionally, this reaction can be severe.

The rash produced by exposure to poison ivy, oak, and sumac is generally treated by a primary care physician, including:

• family physicians,
• internists, and
• pediatricians.

In cases where the diagnosis is not clear, a dermatologist may be consulted.

The diagnosis of this rash is typically made by a healthcare professional after obtaining a thorough history and performing a detailed exam of the skin. While some individuals will know and report exposure to poison ivy, oak, or sumac, others may not be aware of it and may not recall any exposure.

• The appearance of the characteristic rash is usually all that is needed to make the diagnosis.
• No blood tests or imaging studies are necessary.

Picture of the poison ivy plant 

The initial treatment for someone who has recently been exposed to any of these plants includes rinsing the affected area with copious amounts of warm water within 20-30 minutes of exposure to remove the oily plant resin. The effectiveness of rinsing decreases with time, as the oily plant resin is quickly absorbed into the skin. Some authorities recommend rinsing with rubbing alcohol, commercially available poisonous plant washes, or degreasing soaps and detergents. It is also important to scrub under the fingernails to remove any remnants of the plant resin. In addition, thoroughly clean clothing or any objects that may have come into contact with these plants.

If the characteristic rash develops, initial treatment consists of symptomatic care, as in most cases, the rash will improve on its own after one to three weeks. Self-care at home is usually all that is necessary. In the meantime, the following treatments may be useful to alleviate symptoms:

• Apply cool compresses to the skin.
• Use topical treatments to relieve itching, including calamine lotion, oatmeal baths, Tecnu, Zanfel, or aluminum acetate (Domeboro solution).
• Oral antihistamines, such as diphenhydramine (Benadryl), can also help relieve itching.
• For a more severe rash, a healthcare professional may prescribe a high-potency steroid cream or an oral corticosteroid (such as prednisone).
• Over-the-counter pain medication may be necessary for pain control.
• Antibiotics may be prescribed if the rash becomes infected. Avoid scratching the rash to prevent the development of a bacterial infection.
• Go to the nearest emergency department or call an ambulance if experiencing an anaphylactic reaction (severe allergic reaction) characterized by difficulty breathing, difficulty swallowing, facial swelling, or if one has had a previous severe reaction to these plants. Also, seek medical care if the rash involves the genitals or the face or if the rash shows signs of infection.

As above, in the majority of cases, the symptoms can be controlled at home with the aforementioned medications/formulations until the rash resolves. Though different herbal folk remedies have been used in the past, no definite effective therapy can be recommended at this time.

In general, the prognosis is excellent. In the vast majority of cases, the rash will improve on its own within one to three weeks without any complications, and all that is necessary is self-care at home with treatment to relieve the itching.

Some measures can be taken to help prevent the rash caused by exposure to these plants, including the following:

• Learn to recognize these plants to avoid contact with them.
• Wear protective clothing that covers the skin, including gloves, long sleeves, long pants, and boots if in a high-risk area.
• If the possibility of contact with these plants exists, apply commercially available barrier creams to the skin, which may help prevent or lessen exposure to the toxic plant oils. These products usually contain bentoquatam (IvyBlock) and should be applied before going outdoors.
• Do not burn these plants, as this can release urushiol into the air.
• Carefully remove these plants if they are growing near one's home. Be sure to wear protective clothing and gloves.
• Thoroughly wash clothing or any other objects that may have come into contact with these plants, as they can retain the plant oil and cause a rash if worn or touched.
• If a pet has been exposed to these plants, wear protective gloves and bathe them.