You’ll be able to figure out something is wrong; you’ll see sores on your cat’s body and it will be in obvious pain. if the damage is severe, the affected areas of your cat’s skin can break apart, severely wrinkle, or blister. Your vet may also warn you that, if the light sensitivity is severe enough, damage to your cat’s skin may lead to necrotizing (skin death), which leads to secondary infections. The healing process can take a long time for your pet. If your cat is weakened, this could kill it. If the poisonous sap made contact with your cat’s eyes, it could lose its vision.

Giant hogweed, also called Heracleum mantegazzianum, is an ornamental shrub with a highly toxic compound called furanocoumarins and nitrates that cause extreme photosensitivity in animals that have come into physical contact with the shrub or have eaten it. Once these toxins have entered your cat’s body, it will become extremely sensitive to sunlight, especially on areas where it has no hair. The sap works by binding to the DNA and RNA of your cat’s skin.

The symptoms of giant hogweed poisoning are different from other types of poisoning in cats:

Giant hogweed comes from the Apiaceae family and can easily be mistaken for cow parsnip. Giant hogweed is much more poisonous than cow parsnip is. Other names include:

The causes of poisoning by giant hogweed include:

The sap is highly toxic to the skin of cats, humans, and dogs, causing extremely painful burns and even blindness if the sap touches the cat’s eyes. If the cat eats any part of this plant, the toxins will be spread throughout its entire body. While these toxins are throughout the entire plant, the foliage and stems contain the highest levels.

Initial symptoms can develop within fifteen minutes of exposure to giant hogweed. Whether you know what your cat came into contact with or not, once you see that it’s skin is getting so badly burned, it’s time to take it to the vet right away. 

The vet examines your cat and runs a few tests. An exam of your cat allows the vet to observe the condition of its coat of fur. Depending on how recent or advanced the poisoning of your cat is, its reflexes, breathing, blood pressure, temperature and weight also help your vet to determine the correct diagnosis. These include a skin biopsy, which is a skin scraping of the affected skin. They will also examine the tiniest structures of your cat’s skin under a microscope.

Other blood work includes a complete blood count and a blood chemistry profile. In this second test, the vet checks your cat’s levels of gamma glutamyltransferase, bilirubin, phosphatase, and liver enzymes.

After narrowing down your cat’s diagnosis, the vet will begin treating it. The poison needs to be removed from its body, so it will undergo a gastric lavage (stomach wash) and receive activated charcoal to soak up any toxin left in its stomach.

While undergoing treatment, your cat will be kept in a cool, darkened room so it won’t suffer any more skin burns. Once you take your cat home, you’ll need to help the cat avoid bright lights and sunny areas until the photosensitization has gone down. Your vet will also advise you to keep the cat calm, because the new sensitivity of its skin to light can cause debilitation and increase the risk of fatality.

The cat may also receive corticosteroids, either intramuscularly or through an IV. If it begins to develop infections, the vet will treat the wounds and try to keep infections from developing. Painkillers can help to improve its quality of life while it is healing. Antibiotics help to prevent infections from developing. The vet may also apply a bandage to cover any blistered skin areas to protect it from germs, dirt and infection. Depending on the location of the skin burns, your cat may need to wear an Elizabethan (E) collar to prevent it from licking or biting at the area.

Once your cat has come home and begun recovering, help it to remain calm and relaxed so it can continue recovering without unneeded stress. Continue giving your cat prescribed medications for relief of inflammation and pain and to prevent infection from developing.

Keep the cat indoors during daylight hours, unless you apply sunscreen to the affected areas of your cat’s skin. If it goes outdoors, monitor and limit its time outside.

Over time, the burns will heal, although your cat may carry scars for the rest of its life. You may need to teach it how to accept protective clothing, such as light T-shirts that protect previously burned areas of its body. If you allow your cat to go outdoors and remain outside during peak sunlight hours (10am to 4pm), the photosensitivity could return. This remains a risk for several years after the initial contact with giant hogweed. If any of the toxic sap touched your cat’s eyes and it went blind, you’ll need to train it to live exclusively indoors.