Is giant hogweed poisonous to dogs?

Updated 29/09/2023

Blooming mostly in the spring and summer months, the umbrella-like giant hogweed plant can often be found lurking in the depths of the countryside, by riverbanks and footpaths, and even in parks and cemeteries. While green-fingered gardeners and horticulturists alike have been wise to their dangers for many years now, pet parents should be aware that giant hogweed poses a particular risk to our four-legged friends.

So, is hogweed dangerous to dogs - and how dangerous, exactly? Let’s find out.

Is giant hogweed dangerous to dogs?

Yes - giant hogweed (or Heracleum mantegazzianum, to give it its botanical name), is poisonous to dogs, as well as other animals including cats, livestock, and even humans. Both the consumption of giant hogweed and topical exposure (aka skin or fur contact) can cause horrible symptoms and injuries (more on that later) - and it can be fatal. It’s extremely important to contact your veterinary clinic if you suspect your pet may have come in contact with giant hogweed in order to get advice on your pet’s individual case.

Giant hogweed poisoning in dogs

Symptoms

Topical exposure to giant hogweed can cause pain, extreme blistering (that can take months or years to heal - and may cause permanent scarring), swelling, and itchy/red skin. Additionally, sunlight makes the skin sensitive to the irritants in the plant, which can cause a disorder known as phytophotodermatitis (severe photosensitivity to sunlight). If the sap comes into contact with your pet's eyes, it could also cause blindness. 

While the entire plant is toxic, the stem and the leaves contain the highest concentration of toxins - and more dangerous sap can be released if the plant is damaged or broken. While your pet's fur should offer some protection, their ears, eyes, stomach, and mouth are all at risk (particularly if the sap is licked off, rubbed into the eyes, or consumed).

Giant hogweed poisoning can take a few days to appear - for this reason, it can sometimes be mistaken for other skin conditions. If you think your pet has come into contact with giant hogweed, be sure to contact your vet as soon as possible.

Diagnosis

If you suspect your dog has eaten or come into contact with giant hogweed, it's important to act quickly and to contact your veterinarian immediately. If possible, wear protective gloves when handling your pet if you suspect they have been in contact with giant hogweed. To confirm a diagnosis, your vet may prescribe a skin biopsy - this is a painless process that scrapes a sample of the affected skin for further analysis. A full physical exam, including tests to check your pet's temperature, blood pressure, breathing, and reflexes may be prescribed, as well as a full blood count to check your pet's vitals. It’s important to note that several days may pass before the blisters start to show on your pet. Initial symptoms can include irritability, scratching at the affected area, and general discomfort.

Treatment and recovery

Your pet’s prognosis and recovery will depend on the individual circumstances of their exposure, and only your vet will be able to advise you on the correct course of treatment for your pooch. In general, your veterinarian will clean your dog's fur and skin to remove any of the remaining sap, and likely prescribe a skin cream (such as a topical steroid or anti-inflammatory cream), as well as medication to help reduce any pain and swelling. Depending on your pet’s symptoms, your vet may recommend your pet is hospitalised for intensive treatment. This may include IV fluids (a drip) and special medications to help support your pet’s recovery.

Following a case of phytophotodermatitis, your pet may be sensitive to sunlight for many years after, so it's important to keep your dog out of the sunlight following exposure. It's recommended to use sunscreen for dogs or protective clothing, to keep your dog in the shade while outdoors, and to avoid peak sunlight hours. Your veterinarian will advise on the best steps to take for your individual pet.

As with many things, prevention is key: be sure to keep your pet well clear of giant hogweed while out and about on your walkies, and know what to look out for. If you suspect your pet may have come into contact with giant hogweed, contacting your veterinary clinic for prompt advice will give your pet the best chance of making a recovery.

Giant hogweed can grow up to 10-15 feet tall, and has dark green leaves that can reach up to 5 feet in diameter. It has an umbrella-like appearance with tiny white flowers that cluster together, and while often mistaken for cow parsley, the leaves of the giant hogweed tend to be spikier, with purple spots on the stem. Giant hogweed also goes by the following names: 

• Cartwheel plant
• Hogsbane
• Giant cow parsnip
• Giant cow parsley
• Common hemlock

Meet our veterinary expert, Evie

This article has been checked by veterinarian Evie Moloney RCVS. Evie is a vet surgeon who graduated from the University College Dublin, which is the only university offering the veterinary medicine degree in Ireland. She really enjoys surgery and has also worked as an emergency and critical care vet. She is passionate about sharing education about preventative health care 
for pets, especially the importance of regular dog and cat teeth brushing at home. She also enjoys helping owners find practical solutions for keeping pets as comfortable as possible while living with conditions such as arthritis. When not working, she enjoys hiking and swimming. 

Other plants that are poisonous for dogs

So, hogweed and dogs? Not a good mix. Here are a few more poisonous plants for your four-legged friend to avoid: 

• Aloe
• Tulips
• Geraniums
• Peace lilies
• Chrysanthemums