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Giant Hogweed and Its Toxic Cousins

The Bottom Line

Giant hogweed is the most well-known species of the genus Heracleum, a group of plants whose sap contains a chemical that can be very harmful if it touches the skin. Although the concentration of the toxic component can vary from plant to plant, it is best to avoid contact with any species in this group of plants to prevent potential injury!

The Full Story

Heracleum is the genus of a group of plants whose name roughly translates to "of Hercules" or "belonging to Hercules." There are various theories on the origin of its name; some say it's because of the plant's grand appearance and size while others believe it's because Hercules used it for medicinal purposes. The latter, however, is unlikely because no plants of the genus are known to have beneficial medicinal properties. In fact, these plants can be harmful if mishandled.

Heracleum plants can be either biennial (a 2-year life cycle) or perennial (a 3-year or longer life cycle), and their distribution varies across different regions of the world. Some of the more commonly known species include:

Heracleum mantegazzianum (giant hogweed, giant cow parsnip, cartwheel flower)
Heracleum maximum (cow parsnip)
Heracleum sosnowskyi (Sosnowsky's hogweed)
Heracleum persicum (Persian hogweed)
Heracleum sphondylium (common hogweed)

The most notoriously invasive and hazardous species is Heracleum mantegazzianum. This species is native to the Caucasus region but was introduced to the US as an ornamental plant in 1917. Giant hogweed is much larger and taller than the other Heracleum species, growing to be 8-15 feet tall and 3-5 feet wide. It has characteristic hollow, reddish-purple colored stems and produces large, umbrella-shaped clusters of white flowers.

Heracleum plants have toxic chemical compounds called furanocoumarins in their sap. Contact with the clear sap makes skin more sensitive to ultraviolet light and can result in phototoxic dermatitis (an inflammatory skin reaction induced by sunlight). Symptoms range from mild redness and irritation to blisters, burns, and scarring. Additionally, there have been cases of eye irritation and severe eye injury from contact with the eyes. Reactions from the sap can occur within 15 minutes after contact with a peak sensitivity anywhere from 30 minutes to 2 hours later. In severe cases, symptoms can persist for days to months. Not everyone who comes into contact with the sap will have a reaction, but because of the potential to cause significant injury, it is best to avoid contact whenever possible.

Because of its invasive nature and harmful effects, giant hogweed is considered a public health hazard and is classified as a federal noxious weed under the Plant Protection Act, which prohibits importation of the plant into the US and its transportation across state lines. In North America, giant hogweed is most common along riverbanks, in open woodlands, and in abandoned pasture or agricultural lands. Other species of Heracleum like common hogweed and cow parsnip are more widely distributed. They contain furanocoumarins to a lesser degree but still have the potential to cause the same harmful effects.

If you think you have giant hogweed growing nearby, do NOT touch it. Handling and removal of this weed should be done by a professional. If you suspect you've found some, you should contact your local or state agriculture extension service who can help facilitate the removal process. If you happen to come into contact with any portion of the plant, you should immediately wash the affected area thoroughly with soap and water and avoid sunlight for 48 hours. For minor skin irritation, topical steroids like hydrocortisone cream can be applied to help ease discomfort. If symptoms persist or worsen, then it is important to seek medical evaluation. If the sap makes contact with your eyes, immediately irrigate with water for at least 15 minutes. Seek medical evaluation if symptoms do not improve.

If you are worried about exposure to a Heracleum plant, check the webPOISONCONTROL® online tool for guidance or call Poison Control at 1-800-222-1222. Whether you log on or call, expert assistance is available 24 hours a day.

Kristina Yee, PharmD, BS
Certified Specialist in Poison Information

For More Information

Heracleum mantegazzianum, giant hogweed [Internet]. The Poison Garden Website [cited 01 Sep 2019].

Miller AE. Giant hogweed [Internet]. US Department of Agriculture and the University of Georgia; 5 Nov 2003 [cited 01 Sep 2019].

Gucker CL. Heracleum mantegazzianum. In: Fire Effects Information System [Online]. US Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory; 2009 [cited 01 Sep 2019].


Heracleum. Poisindex System [Internet database]. Greenwood Village (CO): Thomas Micromedex. Updated periodically [cited 25 Aug 2019].

Booy O, Cock M, Eckstein L, Hansen SO, Hattendorf J, Hüls J, et al. The giant hogweed best practice manual: guidelines for the management and control of invasive weeds in Europe. Hørsholm (DK): Center for Forest, Planning and Landscape, University of Copenhagen; 2005.

Westbrooks JG, Preacher JW. Poisonous plants of eastern North America. Columbia (SC): University of South Carolina; 1986, p. 177-8.

Bruneton J. Toxic plants dangerous to humans and animals. Lavoisier; 2000, p. 116.


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Prevention Tips

  • If you come across a plant that resembles Heracleum, avoid contact!
  • If you come into contact with any part of the plant, immediately wash the area with soap and water and avoid direct exposure to sunlight.
  • Heracleum is not an appropriate plant for landscaping.

This Really Happened

An ER physician called Poison Control about a 28-year-old woman who had been farming in Sonoma County, California. She came into contact with giant hogweed, borage, calendula, and arugula. That evening, she developed a burning sensation in her hands and came to the ER with skin irritation and blisters. Poison Control discussed the symptoms with the physician and determined that they were likely due to the giant hogweed and made recommendations to provide care with topical steroids, oral antihistamines, and examination by a dermatologist. During a follow-up call by Poison Control the next day, the woman reported reduced swelling after use of a topical steroid.