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Giant hogweed: toxicity, first aid and care
Giant hogweed (Heracleum mantegazzianum, H. sosnowskyi): irritant for cats, irritant for dogs, toxic for small children. The toxic principle, the signs, what to do, and how to grow it.
Cats: IrritantDogs: IrritantChildren: Toxic
Also sold as: Karuputk, jättiputki, Sosnowsky's hogweed.
This is a reference table, not a diagnosis and not veterinary or medical advice. It cannot tell you how much of a plant matters for a particular child or a particular animal — that depends on body weight, on the part eaten and on how long ago. If a person or an animal has eaten part of a plant, phone the poison information centre or a clinician; do not wait for symptoms, and do not make anyone vomit unless you are told to.
What is in it
Toxic principle: Furanocoumarins (phototoxic) — Phototoxic sap.
Not a poison you eat. The sap contains furanocoumarins that are harmless in the dark and become destructive under ultraviolet light: sap on skin plus an hour of sunshine produces a chemical burn. The reaction is phototoxic rather than allergic, which means it happens to everyone, not only to sensitised people, and it can happen the first time.
What it looks like when it goes wrong
Nothing at the time. Redness and burning after about a day, then large fluid-filled blisters over the next two days, healing slowly and leaving dark pigmentation that can last months or years. Sap in an eye can damage sight.
What to do
Wash the skin immediately with soap and water, cover it from daylight, and keep it covered for at least 48 hours. See a doctor for blistering, for large areas, for a child, or for any eye contact. Never strim, mow or brushcut hogweed — that aerosolises the sap over your face and arms.
| Country | Poison information centre | Number | Hours |
|---|---|---|---|
| Estonia | Mürgistusteabekeskus (Health Board) | 16662 | Round the clock; 112 for an emergency |
| Finland | Myrkytystietokeskus (HUS) | 0800 147 111 | Free, round the clock |
| Latvia | Saindēšanās un zāļu informācijas centrs | 67042473 | Round the clock |
| Sweden | Giftinformationscentralen | 010-456 67 00 | Non-urgent advice; 112 in an emergency |
| Norway | Giftinformasjonen | 22 59 13 00 | Round the clock |
| Denmark | Giftlinjen (Bispebjerg Hospital) | 82 12 12 12 | Round the clock |
Anywhere in the European Union, 112 reaches emergency services and can put you through. Lithuania's poison information bureau (Apsinuodijimų kontrolės ir informacijos biuras) publishes its own round-the-clock line; if you do not have it to hand, use 112. For an animal, your own veterinary clinic or its out-of-hours service is the first call — human poison centres do not advise on animals in every country.
How to grow it
| Condition | What it wants |
|---|---|
| Light | Sun; it takes over open ground and riverbanks |
| Water | Damp ground, ditches, verges — it thrives on neglect |
| Temperature | Fully naturalised and spreading across the region |
Nothing to cultivate. Both Estonia and Finland treat hogweed as a regulated invasive species with organised control programmes, so the practical step is to report a stand to the local authority rather than to tackle a big one yourself. Small plants can be dug out with the root crown removed, in full cover — long sleeves, gloves, goggles, face protection — on a cloudy day, and washed off afterwards.
What it gets confused with
Common hogweed (Heracleum sphondylium) is a native, much smaller relative and can also cause phototoxic burns, more mildly. Cow parsley and ground elder look similar at a distance. The giant is unmistakable close up: two to four metres tall, a purple-blotched bristly stem thicker than a wrist, and an umbel the size of a dinner plate.
A plant that is not on the toxic lists
If you are deciding what to keep in a home with a cat, a dog or a small child, this one fills a similar role and is not flagged by the veterinary services.
Source: Royal Horticultural Society — potentially harmful garden plants · checked 2026-09-06
Care guidance is standard horticultural practice for a cool-temperate northern climate. Poison-centre numbers are listed on the hub page and are worth confirming against your own country's health service.
Frequently asked questions
Is giant hogweed toxic to cats?
The veterinary lists rate it "irritant" for cats and "irritant" for dogs. The toxic principle is furanocoumarins (phototoxic). Not a poison you eat. The sap contains furanocoumarins that are harmless in the dark and become destructive under ultraviolet light: sap on skin plus an hour of sunshine produces a chemical burn.
What should I do if giant hogweed sap gets on skin?
Wash the skin immediately with soap and water, cover it from daylight, and keep it covered for at least 48 hours. See a doctor for blistering, for large areas, for a child, or for any eye contact.
Is giant hogweed dangerous for a small child?
The verdict for a child who chews or swallows part of it is "toxic". Nothing at the time. Redness and burning after about a day, then large fluid-filled blisters over the next two days, healing slowly and leaving dark pigmentation that can last months or years.
How do you care for giant hogweed?
Light: Sun; it takes over open ground and riverbanks. Water: Damp ground, ditches, verges — it thrives on neglect. Temperature: Fully naturalised and spreading across the region. Nothing to cultivate. Both Estonia and Finland treat hogweed as a regulated invasive species with organised control programmes, so the practical step is to report a stand to the local authority rather than to tackle a big one yourself.
What is giant hogweed confused with?
Common hogweed (Heracleum sphondylium) is a native, much smaller relative and can also cause phototoxic burns, more mildly. Cow parsley and ground elder look similar at a distance.
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