Giant Hogweed Poisoning

Medically Reviewed by Dany Paul Baby, MD on November 02, 2022
6 min read

Just like poison ivy, you should add giant hogweed to your mental checklist of dangerous plants. Giant hogweed is a poisonous invasive species that was intentionally introduced to the U.S. for decorative purposes. These days, it’s considered a public health hazard.

You should avoid all contact with this plant — any amount of giant hogweed exposure can cause serious skin and eye damage. Learn how to identify this plant on sight. This way, you can keep your family safe when you’re out exploring nature.

Giant hogweed is a member of the genus Heracleum — its scientific name is Heracleum mantegazzianum. The entire genus is filled with poisonous plants, but giant hogweed is one of the most potent and problematic members of the group.

The most dangerous part of the plant is the sap. This is a fluid found throughout all parts of the plant, including the: 

  • Stem — particularly the lower areas
  • Petioles — this is a slim tissue that connects the leaves to the stem, and the sap is more prevalent lower down in the petioles
  • Leaves
  • Flowers

To be safe, you should avoid all parts of the plant unless you’re properly trained and prepared.   

Giant hogweed doesn’t have any current medicinal uses and has a limited culinary range. In Iranian cooking, the dried pods — or fruits — are sometimes used as a spice. This ingredient is called golpar.

One of the most recognizable aspects of giant hogweed is its size. 

As its name implies, giant hogweed is one of the biggest of its kind. It grows an average of 12 to 15 feet tall. 

It has a thick, hollow stem that can measure an average of two to four inches across. That’s about the size of your wrist. The stem is an easily identifiable red-purple color. It’s covered in noticeable bristles.  

The leaves can be as large as five feet wide. Multiple leaves come off of each petiole. Each leaf has deep, sharp incisions along its edges. This makes them look jagged.  

The plants are topped by a recognizable flower in the spring. Clusters of small white flowers form broad, umbrellalike shapes at the top of the plant. The entire inflorescence — or cluster of flowers — can be up to 2.5 feet across. In most areas in the U.S., you’ll find them in bloom in mid-May through July. 

After the flowers bloom, they form rounded seed pods in the region where the flowers were located. These are present through the fall. 

Giant hogweed is native to the Caucasus region — which includes countries like Georgia, Armenia, and Azerbaijan. For a brief period of time, people used it as a decorative addition to the landscape. It was intentionally introduced to most of Europe, Great Britain, Canada, and the U.S. — where it’s now considered a problematic invasive species. 

In the U.S., it first became established in a handful of states, including: 

  • New York
  • Pennsylvania
  • Washington

The seeds are spread through bird droppings, so the plant’s range slowly increases with time. 

The environments where the giant hogweed thrives the most include open areas along riverbanks and train tracks and in a forest’s openings. But the plant could crop up anywhere with moist soil. It’s even been found in the middle of urban lawns.

Contact with giant hogweed can cause a severe reaction. The plants contain toxins called furanocoumarins. These are mostly found in the sap as well as throughout the plant’s tissues.

These toxins work through direct contact with your body. This can happen if you: 

  • Directly touch the plant with your bare skin
  • Touch tools or clothing that came in contact with the plant or its sap
  • Get sprayed by sap from the plant — the sap can travel up to four feet away during removal efforts, so keep a safe distance at all times

The severity of your reaction depends on how much of the toxin you encounter and the body parts that it touches. Luckily, giant hogweed poisoning rarely requires immediate emergency attention. But you’ll still need to take steps to limit the extent of your reaction.  

Your body will begin reacting to giant hogweed shortly after contact. Some changes may begin as soon as 15 minutes after you’ve touched the toxin. You’ll likely notice significant irritation anywhere from 30 minutes to two hours after contact.

After that, symptoms can continue to develop for the first 24 to 48 hours. Mild cases will peak at three days and then start to improve. Severe cases can create problems for weeks to months after your exposure. Scarring could last up to six years after the event.

The main effect of the toxin is to make your tissues more sensitive to UV light — so sunlight is particularly dangerous after exposure. The exact symptoms depend on which of your body parts touched the toxin and the amount of sunlight you encountered.  

If the toxin gets on your skin, giant hogweed symptoms can include: 

  • Irritation
  • Redness
  • Blisters — these can be painful and build up a dark pigmentation over time
  • Burns
  • Scarring
  • Phototoxic dermatitis — this is a severe skin reaction that’s based on the amount of sun exposure, and it’s an exacerbation of all of the above symptoms
  • Long-term light sensitivity — the affected region could remain UV sensitive for months after your exposure 

If the toxin gets into your eyes, giant hogweed symptoms can include: 

The best giant hogweed treatment depends on how severe your reaction is. If you know that you’ve touched the plant, then you should immediately wash the affected area with soap and water. Avoid touching your eyes at all costs. Make sure to change and wash your clothes too in case the toxin is on the fabric. 

If the irritation is minor, then you should apply a topical steroid — like hydrocortisone cream — to relieve your symptoms. You’ll only need to get medical attention if the problem lasts a long time or if it gets a lot worse within the first 48 hours after exposure. Severe open wounds and painful blisters may require a medical evaluation. 

Even if the irritation is mild, you should carefully apply sunscreen to that area and keep it covered up for weeks, months, or even years after your exposure. This will prevent the irritation from returning or getting worse over time. 

The toxin is most problematic if it gets into your eyes. Immediately wash your eyes for 15 minutes straight if you think that they’ve been exposed. This means that you have to find a clean source of running water, hold your eyelids open, and keep water moving across your eye for the entire 15 minutes. 

Your safest bet is to contact your doctor or seek expert advice after you’ve taken the time to rinse your eye. Wear UV-blocking sunglasses when you go outside. 

You can always call Poison Control — at 1-800-222-1222 — or message them on their website if you have questions or concerns.  

Never try to remove giant hogweed by yourself. Local and state agricultural extension services send experts to remove these plants for free. Take a picture of the plant and check the web for the best service to contact in your area. 

An important fact to keep in mind about giant hogweed is that many of the plants that look like it can cause similar symptoms — like wild parsnip and a variety of hemlock species. But others are safe and are even used in traditional medicine.   
Examples of similar-looking plants that are reasonably safe include: 

  • Angelica atropurpurea. This looks a bit like miniature giant hogweed. It’s less than 8 feet tall with dozens of small leaves per petiole. It has a long history as a medicinal herb.
  • Queen Anne’s lace. This is a relatively common plant that has smaller versions of the giant hogweed’s flowers. 
  • Valerian. This smaller plant is frequently used in traditional medicine. It has a profusion of small white flowers that are less flat than giant hogweeds. Its compound leaves are more numerous and much smaller.  

Overall, your safest bet is to avoid all plants that look like giant hogweed — both large and small — unless you know exactly which species you’re dealing with. Even if it’s not giant hogweed, it could be a similarly poisonous relative.