In this guide, we’ll discuss five of the most common rash-causing plants, describe how to identify them, and what skin reactions typically happen.
Useful Terminology for Identifying Plants That Cause Rashes
Before we jump into our list, we’re going to cover some basic leaf shapes and types. Knowing what these plant identification terms mean will greatly increase your chances of accurately identifying one of these rash-causing plants. We’ll use some of these terms throughout the article to describe how to identify the plants.
3 Basic Leaf Types:
Compound Leaf- A compound leaf refers to a leaf that consists of two or more leaflets originating from the same place on the plant stalk. When you see a compound leaf, you may think you are looking at multiple leaves, but they are actually leaflets that make up the compound leaf. Simple Leaf- A simple leaf is made of one leaf blade that is not divided into two or more leaflets. Even if it has deep indentations along the margins, it will always only originate from the stem at one point. Needle-like Leaf- Occurs on plants like pine and fir trees. They have long, narrow, needle-like leaves that are often covered in a protective, waxy layer.
Common Leaf Shapes:
Oblong- Oblong leaves are long, oval leaves Ovate- Leaves that are widest towards the base and taper to round or pointed ends. Lanceolate- long, narrow leaves that taper to a point. Scalloped- Leaves with rounded scallop shapes along the margin. Lobed- A lobed leaf is deeply divided along the margin, which creates several equally spaced lobed sections of the leaf.
Watch Out for These Plants That Cause Rashes
Now that you have some useful terms to help you identify these five rash-causing plants, let’s jump into the list!
1. Poison Ivy (Toxicodendron radicans)
The plant that most likely comes to mind when people talk about plants that cause rashes is the infamous poison ivy (Toxicodendron radicans). A member of the Anacardiaceae that includes sumac plants, mangos, cashews, and pistachios, poison ivy, also commonly called Eastern poison ivy, is a rash-causing vine commonly found across North America and parts of East Asia. The rash is caused by a chemical that poison ivy contains, called urushiol. This oily chemical spreads across the skin and leads to a rash. If you come into contact with a poison ivy plant, change out of your contaminated clothes and wash affected areas with soap and warm water as soon as possible to help remove the urushiol oil. You’ll want to wash clothing and any tools that also came into contact with the plant as the oil can stick to these items as well.
To Identify
Look for compound leaves growing in sets of three ovate leaflets that are sometimes mildly lobed. The leaflets are arranged so that there is always a middle leaflet with a slightly elongated stem. The other two leaflets are always directly opposite from one another. As a climbing vine, you can typically find poison ivy growing up fences, walls, and trees. It often grows in disturbed areas, such as a recently logged site. When poison ivy first emerges in the spring, the leaves are red-orange, but change to green as they mature.
Effects of the Rash
After touching any part of poison ivy, you may experience itchy blisters appearing along your skin. This rash often begins to appear within hours or a couple of days after exposure. The rash can continue to appear and remain incredibly itchy for a couple of weeks. In addition to itching and blisters, signs and symptoms of exposure to poison ivy also include redness and localized swelling. A common misconception is that the rash can continue to spread by itching the blisters that commonly ooze a clear liquid. This liquid is actually a beneficial serum that our bodies create to help fight against infection. It’s best to not fervently itch the rash, however, so that the blisters will heal faster, and to prevent scarring from repeated scratching.
2. Giant Hogweed (Heracleum mantegazzianum)
A tall herbaceous plant in the carrot family (Apiaceae), giant hogweed causes significant rashes from its poisonous sap. Native to the Caucasus region of Europe and Central Asia, giant hogweed is now considered an invasive species in North America.
To Identify
At maturity, this plant should stand about 10-15 feet tall with umbrella-shaped clusters of tiny, white flowers that have the appearance of lace (resembles the flowers of Queen Anne’s lace). This plant flowers from late June through mid-July. Look for large, deeply lobed green leaves with pointed tips. These leaves can span 5 feet at maturity. The stalks are light green, hollow, and about 2-4 inches in diameter. Covering the stalks are tiny purple splotches and short, stiff hairs. This plant can resemble its carrot family relatives such as cow’s parsnip, wild parsnip, and Queen Anne’s lace. If you suspect you’re looking at giant hogweed, never touch the plant without proper protective equipment. Always consult several reputable sources for identification.
Effects of the Rash
The sap of giant hogweed contains chemicals called furanocoumarins. When these chemicals come into contact with our skin followed by UV light exposure (such as from the sun), a condition called phytophotodermatitis occurs. This condition causes a red rash to appear followed by severe blistering within 24 hours. The severity of the blisters can lead to scarring that lasts months up to 6 years. Long-term sun sensitivity can occur as the chemicals in giant hogweed disrupt the skin’s ability to protect itself from the sun. The effects can become life-threatening if enough of someone’s skin comes into contact with the rash. Third-degree burns can result from phytophotodermatitis if you do not take fast action to thoroughly wash the skin and stay out of the sun for at least 48 hours.
3. Poodle-Dog Bush (Eriodictyon parryi)
A perhaps lesser known of the plants that cause rashes, poodle-dog bush (Eriodictyon parryi) is a native plant to the arid regions of California. It commonly grows along disturbed areas such as trails and in areas recently burned by wildfires (plants that do this are known as fire followers).
To Identify
This lovely shrub has showy, bell-shaped lavender-purple flowers that bloom from June through August and grow along clusters of vertical stems. It can grow up to 10 feet tall and almost exclusively grows in disturbed areas. It most commonly grows in areas with elevations between 3,300 and 7,500 feet. As it is a short-lived plant that recedes once other native plants recolonize a disturbed area, people typically only see it at shorter heights of 2-5 feet tall. It has simple, lanceolate leaves with tiny serrations along its margins. The pale green leaves can range from 2-11 inches long. Tiny, sticky hairs cover its stems and leaves. Especially when in bloom, it has a strong musky odor that some liken to the smell of cannabis plants.
Effects of the Rash
The tiny, sticky hairs of the poodle-dog bush secrete a toxin upon contact that causes a rash similar to that of poison ivy. After exposure, you can expect a rash to appear within a couple of hours or days. Signs and symptoms include redness, swelling, blisters, and intense itching. Similar to dealing with poison ivy, the best course of action after exposure is to thoroughly wash with warm soap and water.
4. Cashew Tree (Anacardium occidentale)
You may be surprised to learn that the cashew tree (Anacardium occidentale) is closely related to poison ivy. Like poison ivy, the cashew tree is in the Anacardiaceae family and contains the rash-causing chemical, urushiol. Native to Northeastern Brazil, people now cultivate cashew trees in tropical regions around the world.
To Identify
At maturity, the cashew tree can reach about 35 to 40 feet tall. It’s a bushy tree with many low-growing branches. It is rather bare towards the trunk with wide, oblong simple leaves along the mid-section and ends of the branches. When in bloom, it produces clusters of tiny pink-red flowers that branch off along the main stem. The flowers consist of 5 small, delicate petals. During fruiting, the cashew tree produces a cashew nut that hangs below, and is attached to, a pear-shaped yellow or red accessory fruit. The cashew nut is encased in a double shell that contains rash-causing toxins.
Effects of the Rash
Like poison ivy, the leaves, stems, and roots of cashew trees contain urushiol. The exterior shell of the cashew also contains urushiol, and as such, you should not handle it without protective clothing. To be safe for handling and consumption, people generally roast cashew nuts and sell them without their shells. If you come into contact with the oil, expect an itchy, blistering rash similar to that caused by poison ivy exposure.
5. Stinging Nettle (Urtica dioica)
Native to Europe and now widespread throughout the world, stinging nettle (Urtica dioica) is an herb widely studied for its medicinal properties that also cause skin irritation upon contact with its stinging hairs. Stinging nettle has had a documented history of medicinal use that dates back to at least 2,000 years ago. Historically, people have used the plant as a diuretic, laxative, and as a remedy for chronic rheumatic pain. Today, studies support the use of stinging nettle for anti-inflammatory purposes, including rheumatic inflammation.
To Identify
Stinging nettle is an herbaceous plant that can grow up to 6 feet tall and about 1-foot wide. Typically, it grows in forests and meadows along the forest edge. The leaves are deeply veined, heavily serrated along the margins, heart-shaped, and tapered at the end. The leaves are oppositely arranged as they grow up along the main stem. The plant is densely covered with tiny stinging hollow hairs.
Effects of the Rash
The tiny hollow hairs that cover stinging nettle act like tiny needles that inject irritants into the skin upon contact. These irritants include histamine, formic acid, and acetylcholine. The rash normally appears immediately after contact and causes burning and itching. Sometimes, the rash can blister, though this is not as common as it is with plants that contain urushiol. The rash can subside within minutes to days depending on the sensitivity of the individual.
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