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Hogweed Burns

Published on August 3rd 2019
A close up of a flower
A common sight along roadside verges and riverbanks, hogweed is a statuesque wildflower with a bit of a reputation.
Although our native hogweed can cause blistering, its invasive cousin, giant hogweed, causes serious skin issues and is a blight along our watercourses.
The plant often makes summer headlines for the wounds it causes, particularly to children.
A tree next to a body of water
Giant hogweed is a serious pest species which crowds out native wildflower species and destabilises riverbanks.


Hogweed is a member of the carrot family and also goes by the name of cow parsnip. It may come as a surprise that a plant with blistering sap is related to the humble carrot, however, many herbs are also in this family:

Wild Carrot

Daucus carota

Sweet Fennel

Foeniculum vulgare var. dulce

Flat-Leaved Parsley

Petroselinum crispum var. neapolitanum

Furthermore, for as unpleasant as giant hogweed is, the hemlocks are far more poisonous so always forage with extreme caution. Plants in this family are known as umbellifers due to the broad, flat shape of their flowers.
Hogweed is a biennial or perennial plant, forming a large rosette of coarse, grey-green triangular lobed leaves in its first year. These leaves can grow to around 60cm (2ft) in length. During its second year, the plant sends up a flower stem reaching roughly two metres in height (6ft).
Due to its size, the only other plant you are likely to mistake hogweed for is giant hogweed. This plant’s leaves are more pointed in appearance, and it lives up to its name with a five-metre (16ft) tall flower stem. Giant hogweed sap is far more corrosive than our native hogweed.

Hogweed sap

Unusually, hogweed sap it is phototoxic, meaning that the sap doesn’t take effect fully until the skin is exposed to sunlight.
For this reason, children who use the hollow stems as pea shooters don’t feel the burning sensation immediately. The same can happen with gardeners attempting to remove this invasive weed.
A close up of food
The hollow stems are brimming with sap, and even plant hairs on the stems and leaves can cause blistering. It is best to tackle hogweed at night.
For those who are interested, giant hogweed sap contains photosensitising furanocoumarins (a type of chemical compound produced by plants). These can cause a painful reaction on the skin when exposed to sunlight, known as photodermatitis.
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Giant hogweed causes what looks like extreme sunburn. This is because the sap strips the skin of its ability to protect itself from the sun’s rays, leaving it vulnerable to damage.
Heat and sweat can exacerbate the symptoms, which usually begin to show around 15 minutes after contact. Within two hours, ugly blisters will start to form and become darker over the next couple of days.
It can take over a week for the blisters and soreness to subside, though scarring can take several months to disappear.
A sign on a wooden pole
It is best to avoid areas where hogweed has taken over. If you are looking to control it on your own land be sure to use PPE such as gloves and a mask.
Unfortunately, in many cases, the sap can cause long-term sensitivity to sunlight. In very severe cases, the sap can cause blindness if it gets into the eyes and is exposed to sunlight.


If you do come into contact with giant hogweed sap, wash with cold water and soap immediately.
Keep the affected area out of sunlight for a good couple of days if you do develop symptoms. Use topical steroids to ease discomfort and help reduce the reaction.
If unsure, seek medical advice – it’s always better to be safe than sorry.
A hand holding a black object
OUCH! The nefarious giant hogweed strikes again.

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