Plant-Induced Contact Dermatitis

You don’t have to be a gardener or hiker to end up with a mysterious rash or blisters because you got too close to the wrong plant. In New York we have plenty of plants that cause itching, rashes, and/or blistering of the skin from even the slightest contact. And in the case of some irritants, animals or items that came in contact with the irritant/allergen can transfer it to other animals and people.

There are many plants that are not on this list, but still may cause a reaction, because some people are more sensitive than others. A few people are allergic to pine needle sap; but, in general, it is not a plant people think of when it comes to skin irritation. Anything can cause irritation given the right circumstances, but let’s look at the most common:

1. Poison Ivy (Toxicodendron radicans) – The most common cause of blistery patches combined with intense itching. The cause is a protectant it exudes on its leaves, urushiol oil, that most humans are highly allergic to with any skin contact. It can cause very serious reactions if it is eaten or inhaled (e.g., if burnt in a campfire). For identification, it is one of the plants that we should tell children, "Leaves of three, let it be." Its shiny dark green leaves can often be found climbing trees or telephone poles as well as at the edge of lawn, woods, and roads. Extreme caution should be used if you plan on weeding it from an area. Also, be careful with pets who may have been exposed. The oil can transfer from their coats to humans. Additionally, gloves, sleeves or other protective gear that may have come in contact with the plant can also transfer the oils. Soaking & washing with hot water and heavy-duty detergent, especially something designed to break down oils and/or grease, is a critical action when you think clothes may have been exposed.

2. Poison Oak (Toxicodendron pubescens) – a much less common plant found in New York but is present in sandy or coastal areas. It is much more common in the Southeast but as climate warms, it may widen its area. It also contains urushiol and the same cautions as above should be observed.

3. Poison Sumac (Toxicodendron vernix) – Sumac is a much larger bush/tree and not a vining plant like poison ivy or poison oak. It also produces urushiol oil. To complicate matters, there are sumacs that are edible, or at least, non-toxic. But they are all similar looking so unless you are going to pull out an ID guide, all sumacs should be avoided. Poison sumac prefers wet swampy areas.

There is also quite a list of other plants that can cause issues ranging from serious burns to just some itchy patches that can be reduced in severity with some soap and water. Again, this list is not exhaustive, and anyone could be allergic to anything. Let’s start with the worst and move to least irritating.

4. Giant Hogweed (Heracleum mantegazzianum) is very nasty in the kind of blistering it can cause. Any plant sap, containing furocoumarin, plus sunlight and moisture (sweat) leads to huge areas of blistering. This combination is known as photodermatitis. Within 24-48 hours of contact, huge areas of blisters form. If the sap gets into the eyes, it can cause temporary or permanent blindness. This can be a severe problem for anyone who has large areas affected and can often lead to hospitalization. Scaring can be significant in the affected areas.

The plus side, if there is one to this plant, is that it is a G-I-A-N-T. When fully grown its umbrella-like stalk and flower head are 7-14 feet tall with leaves as wide as 5 feet and the flower umbel can be 3 feet wide. It’s not nearly as sneaky as some of the other toxic plants so it should be easy to avoid.

5. Cow Parsnip (Heracleum maximum) is also an excessively big weed that looks like Hogweed and can cause blistering. Not quite as big nor as nasty as Giant Hogweed but still should be avoided.

6. Wild Parsnip (Pastinaca sativa) also causes phytophotodermatitis. This is a common weed in New York as a roadside or field-edge dweller. It looks like a smaller version of Giant Hogweed and Cow Parsnip but with yellow umbelliferous flowers.

7. Poison Hemlock (Conium maculatum) can cause skin irritation but that is uncommon. While it rarely causes skin irritation, this plant contains coniine and other alkaloids that are extremely toxic when ingested. Even small amounts absorbed through cuts or mucous membranes can be dangerous. Always wash hands after contact.

8. Carrots, Parsley, Celery in the garden can also cause contact dermatitis from furocoumarins and psoralens. Although uncommon, it is possible. Plants in this group also cause food allergies.

9. Pokeweed (Phytolacca americana) can cause skin irritation from phytolaccatoxin and phytolaccigenin. It must be noted that inhalation of the pollen has been known to cause lung irritation as well. All parts of the plant are poisonous if ingested.

10. Stinging Nettle (Urtica dioica) has tiny hairs that inject histamine and formic acid. This causes immediate burning and itching. Washing to remove the hairs is a good first step in controlling the irritation but it usually subsides in a few hours.

11. Buttercups (Ranunculus spp.) Yup, sweet buttercup contains ranunculin, which turns into the blistering agent protoanemonin when the plant is crushed. Contact can cause redness, blisters, and skin discoloration as burns heal.

12. Prickly Lettuce (Lactuca serriola) This plant causes rashes by mechanical means. The sharp hairs or spines on the leaves and stems get imbedded in the skin causing irritation. Washing off the spines quickly can reduce irritation. Some people have more marked allergic responses than others. This plant has also been known to cause lung irritation from inhaling the pollen.

13. Chrysanthemum spp. They produce allergenic compounds, sesquiterpene lactones, which cause contact dermatitis that displays as a red, itchy rash. People can also be allergic to the pollen, causing respiratory symptoms.

14. Milkweed (Asclepias syriaca L.) Although used in traditional medicines, every part of the plant is toxic when ingested. The sap of milkweed contains cardenolides which can cause skin irritation.

15. Tree of Heaven (Ailanthus altissima) is a very heavy pollen producer and can cause allergic response. Contact dermatitis can occur from any plant parts (leaves, branches, seeds, and bark) and products. Rarely, it has been reported that exposure to sap through broken skin has resulted in myocarditis (inflammation of the heart muscle).

16. Goldenrod (Solidago spp.) Contact with this plant and the pollen can cause rashes. Pollen is well-known for causing allergic reactions.

17. Ragweed (Ambrosia spp.) Pollen from plants causes respiratory allergic reactions and can also cause skin reactions.

Again, this is not an exhaustive list. Many more green meanies as well as sun, insects, and the compounds we use to protect ourselves can make humans red, bumpy, and itchy!

What to do to help reduce risk?

• Wear gloves and long sleeves when gardening or hiking.
• Learn to identify plants. The internet is awesome for this. There are multiple pocket guides on smart phones. Caution though as the apps that identify from taking a picture can be quite unreliable/inaccurate. Use reliable websites/apps that use keys to properly identify.
• Wash skin immediately with soap and cold water after potential exposure.
• Wash contaminated clothes thoroughly and alone in the washer.
• Do not burn poisonous plants—urushiol can become airborne and affect lungs.

Vocabulary That May Be Handy

In identifying and treating rashes, it can be helpful to talk-the-talk of the medical professionals one might interact with. Here are just a few terms that can help describe/diagnose rashes:

• Dermatitis: A broad term for skin inflammation, encompassing conditions like eczema (atopic dermatitis), contact dermatitis, and seborrheic dermatitis.
• Vesicles: Small, fluid-filled blisters
• Bullae: Larger, fluid-filled blisters.
• Papules: Small, raised bumps on the skin.
• Macules: Flat spots of discoloration on the skin.
• Urticaria (Hives): Raised, red, itchy welts on the skin, often triggered by allergies or sensitivities.
• Exanthem: Widespread rash eruptions, often accompanied by fever and fatigue, often seen in children.
• Erythema Multiforme: An allergic reaction causing a rash, sometimes with mouth sores, and can be associated with various infections or medications.
• Heat Rash (Miliaria): A rash with tiny red bumps or blisters.
• Nummular Lesions: Coin-shaped, round lesions.
• Linear Lesions: Lesions arranged in a line, often caused by scratching.

Good luck out there and enjoy the season without irritation!

Note: This article is for informational purposes only. It does not provide medical advice. Consult a healthcare provider for any rash, especially if it worsens or is accompanied by other symptoms.

For more information:

https://dec.ny.gov/nature/animals-fish-plants/plants/harmful-plants

https://www.scenichudson.org/viewfinder/dont-touch-that-plant/

https://plants.usda.gov/

Last updated June 26, 2025