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Poison Ivy, Oak, and Sumac: Most Common Cause of Allergic Contact Dermatitis

Poison Ivy, poison oak, and poison sumac are all responsible for the highest number of visits to poison centers in the US. Because of their irritant abilities, they’re a generally well-known collection of species within North and South America and Asia where they’re native. They’re members of the toxic Toxicodendron genus and they’re also part of the cashew family (Anacardiaceae).

Poison ivy (Toxicodendron radicans) is one of the most well-known species of this genus. It’s a climbing plant that’s native to eastern US states, however, it’s not an official member of the ivy genus (Hedera). There is also a western poison ivy species in the US known as T. rydbergii. Poison oak has the Latin name ‘Toxicodendron diversilobum‘, and poison sumac is known as ‘Toxicodendron vernix‘ and is also sometimes known by the colloquial name ‘thunderwood’.

A hanging branch with bright orange, pointed oval leaves of the Poison Sumac, with a dense woodland scene behind.
Poison sumac or ‘Thunderwood’ (Toxicodendron vernix) in the autumn | Photo by John Barber on Wikimedia Commons

Poison ivy, poison oak, and poison sumac are all warily avoided by hikers, campers, and anyone exploring the outdoors, but what makes them so potent?

What Are The Active Compounds in Poison Ivy, Oak, and Sumac?

All species within the Toxicodendron genus contain an oil known as urushiol. It can cause severe skin irritation and a very serious allergic reaction in some people. It’s a clear liquid, which isn’t noticeable until it begins to severely burn, blister and irritate the skin.

Poison Ivy, Oak, and Sumac Poisoning Symptoms

When it touches the skin, urushiol will begin to cause contact dermatitis, and most people will develop an incredibly itchy and painful rash. The uncomfortable itch can last for weeks, so basic knowledge of the plant is essential to avoid contact.

Like manchineel, when poison sumac is burned, the resulting smoke can cause damage within the lungs, and in extreme cases, it can be fatal.

Photo showing numerous poison ivy leaves with the characteristic three leaflets. The dull waxy sheen is also noticeable.
Poison Ivy (Toxicodendron radicans) | Photo from Wikimedia Commons

Cultural Symbolism of Poison Ivy, Oak, and Sumac

In China, Korea, and Japan, the Chinese lacquer tree (T. vernicifluum) is traditionally cultivated for a number of uses. The sap can be extracted and used to create a lacquer that gives a glossy finish to wooden products like tabletops, weapon handles, and musical instruments. The fruits are also used to produce wax which can be molded into candles or used as furniture wax.

A large cluster of off-white fruits and orange and yellow leaves behind.
Fruits of the Chinese Lacquer Tree (Toxicodendron vernicifluum) | Photo by Aomorikuma on Wikimedia Commons

What is the Medicinal Potential of Poison Ivy, Oak, and Sumac?

Within China, the fruits have been used in traditional herbal remedies to stop bleeding and even rid the body of parasites. Today, however, usage is much less common, and studies which examine its medicinal potential are limited.

What Does Poison Ivy, Oak, and Sumac Look Like?

The leaves of all three plants tend to have a slight waxy sheen which can help in identifying them. This dull sheen is the urushiol which causes severe skin irritation. The leaves of poison oak and poison ivy usually consist of three leaflets, which can be a useful identification feature. Also, poison oak leaves tend to be lobed in a similar way to true oak leaves.

Characteristics can vary heavily depending on the location and habitat. Some species and varieties may be a low-growing vine, others a small woody shrub. The fruits are usually an off-white color, and the leaves will flush red in autumn.

Bright green, glossy leaves on the poison oak.
Poison Oak (Toxicodendron diversilobum) with its oak-shaped leaves | Photo by Ryan McMinds on Wikimedia Commons

Where Does Poison Ivy, Oak, and Sumac Grow?

Poison Ivy, Oak, and Sumac can grow in a variety of habitats — from dunes and tropical rainforests to mountainous slopes and forests. They can also establish quickly in disturbed soil, either at field edges or construction sites.

One of each species can be found in all US states apart from Hawaii and Alaska. They are native only to the US and also to areas within Asia, but have been naturalized in some areas within Australia. There are no species of this genus currently found in Europe, Africa, or the UK.

An exposed poison ivy branch with several large clusters of tiny green flowers.
Photo of Poison Ivy (Toxicodendron radicans) in flower | Photo by Fritzflohrreynolds on Wikimedia Commons

Conclusion

Studies have concluded that climate change may be making poison ivy and other members of the Toxicodendron genus more potent. They thrive in conditions with a high carbon dioxide count, and the rigorous growth could be changing the urushiol and making it more allergenic.

While many people see poison ivy, oak, and sumac as undesirable weeds, their fruits are relied upon by lots of bird species. Plus, like the toxic manchineel, their solid root system helps to stop soil and sand erosion.

Featured Image | Poison Ivy in Minnesota, by Hardyplants at English Wikipedia

0 thoughts on “Poison Ivy, Oak, and Sumac: Most Common Cause of Allergic Contact Dermatitis

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