Many common plants can cause hives or other allergic reactions. These plants usually have distinct features that you can use to avoid them.
Going for a hike or a picnic can sometimes lead to itchy hives. Brushing up against certain plants can irritate your skin, causing painful stinging and blistering.
Many people are familiar with toxic plants like poison ivy, poison sumac, and poison oak, but they’re not the only plants that can cause an allergic reaction. You can find poisonous plants throughout the county growing in woodlands, riverbanks, beaches, and backyards.
Most toxic plants have a distinct appearance that can help you avoid them.
Multiple plants can cause hives. In the United States, you’re most likely to run into these seven.
1. Poison ivy
Poison ivy is one of the most common and well-known poisonous plants. It can be found throughout the United States, except for the West Coast.
It grows in wooded areas, parks, backyards, fields, along roadsides, up trees and fences, and many other outdoor areas. The plant is identifiable by its distinct threefold green leaves and clusters of greenish-white fruit.
Poison ivy causes hives because the sap contains a toxin called urushiol oil. This toxin irritates your skin on contact. Typically, a poison ivy rash causes itching and blisters and shows up a few days after coming into contact with it.
2. Poison oak
Poison oak grows in forests and in dry locations, such as beaches and fields. It’s most common on the West Coast and least common in the Midwest. Poison oak is very similar to poison ivy. It contains the same urushiol oil that can irritate your skin, and it causes the same reaction.
Poison oak also has three leaves, although the leaves are typically a darker green than poison ivy leaves. Additionally, poison oak has hairy yellow flowers, and its fruit is fuzzy, while poison ivy’s fruit is smooth.
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3. Poison sumac
Poison sumac also contains urushiol oil. It causes a similar rash and reaction to poison ivy and poison oak. Unlike those two plants, poison sumac grows as a small tree or shrub. It primarily grows in wet areas and is often found near ponds, rivers, and streams in warm areas such as the Southeast.
Poison sumac has red stems that lead to green leaves with 7–13 leaflets. Its flowers are a greenish-yellow color. It grows berries that are white or pale green and hang below the branches.
There is a nonpoisonous version of sumac, but this plant produces red flowers and red berries.
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4. Stinging nettle
Stinging nettle grows throughout the United States and the world. It’s often near streams, as well in ditches, along hiking trails, and on farmland, and grows in dense patches.
Stinging nettles have singular stems with green or purple branches that grow up to 8 feet. These branches can have stinging hairs, which inject a blend of histamine, formic acid, serotonin, and acetylcholine into the skin upon contact.
Stinging hairs can also be found on the plant’s leaves. Stinging nettle leaves have a pointed tip and are 2–4 inches long. The leaves are dark green, and white flowers grow under them.
If you touch a stinging nettle, you’ll feel a sharp sting, followed by a burning or itching sensation and hives that can last for up to 24 hours. While the plant can be medicinal, it’s usually best to avoid it in the wild.
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5. Leadwort
Leadwort is a shrub that can thrive in the climate of the Southeastern United States. Leadwort has shiny green leaves that turn redder in the fall. It also has blue flowers that bloom from spring until fall and turn a deep shade of red over the winter. Touching any part of this plant can cause blisters.
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6. Wild parsnip
The sap of wild parsnips contains a toxin called furocoumarin that is sensitive to sunlight. It can cause blisters like those caused by a burn.
Wild parsnips are between 2 and 5 feet tall with hollow stems. They have long, narrow leaves that can be up to 18 inches with 3–15 yellow-green leaflets. Round, yellow flower clusters grow along the stem.
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7. Giant hogweed
Giant hogweed is an invasive species originally found in Asia. Contact with the sap of the giant hogweed can lead to a serious reaction, including blistering, a rash that resembles a second-degree burn, scarring, eye irritation, lasting sensitivity to sunlight, and even blindness.
The sap from giant hogweed is phototoxic, meaning it won’t become active without exposure to ultraviolet light. You can prevent a reaction by washing the exposed area and avoiding sunlight for 48 hours.
Giant hogweed plants can be over 14 feet tall. They have hollow green and purple stems covered in white hairs with leaves that can be up to 5 feet across and white flowers that are umbrella-shaped and can be up to 2 1/2 feet across.
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Many plant allergy hives and rashes cause blisters and raised red areas. The reaction you have will depend on how much of the toxin you came into contact with, the specific plant, and how sensitive your skin is to the toxin. You can see some examples of plant allergy hives in the images below.
Many times, you can treat plant allergy hives or rashes at home with simple self-care steps. If you or someone in your household has a reaction after coming into contact with a plant, you can take the following steps:
- Remove any fine hairs: If you came into contact with a stinging nettle, you might still have fine hairs in your skin. You can remove these hairs with duct tape or medical tape.
- Wash the area: Thoroughly wash the area that came into contact with the toxic plant. You can use an antibacterial soap or body wash.
- Try a cold compress: If you’re experiencing swelling or itching, a cold compress can help soothe your skin.
- Apply over-the-counter (OTC) anti-itch creams: Creams like calamine lotion can help your skin heal faster and reduce your symptoms. Your local drugstore should have several options.
- Take OTC antihistamines: Antihistamines are medications that you can take to help reduce itching and irritation. One example is Benadryl.
- Soak in an oatmeal bath: If you have an especially large rash or hive reaction, an oatmeal bath may help soothe your skin.
When to seek emergency care
Sometimes, an allergic reaction can be a medical emergency.
If you or someone around you has been exposed to a toxic plant and is having difficulty breathing or has lost consciousness, call 911 or emergency services immediately.
Contact with some toxic plants can lead to itchy, painful hives. Plants like poison ivy are common and typically cause a minor reaction. Others, like giant hogweed, are invasive species and can lead to serious complications such as blindness and scarring.
If you come into contact with a toxic plant, washing the area with soap and water, removing any stinging hairs, using OTC creams, and taking OTC antihistamines can help. If your reaction is severe, seek immediate medical attention.