Warning over dangers of giant hogweed to humans and pets

South Wales Argus

27-07-2025

Giant hogweed can cause 'severe burns' that reappear for years and can 'even lead to blindness', specialists warn.
This highly invasive plant, with its toxic sap that causes photosensitivity, is found along river paths or woodland and should be treated with 'extreme caution'.
What is giant hogweed, and is it dangerous?
Giant hogweed, also known by its Latin name Heracleum Mantegazzianum, originated in Southern Russia and Georgia.
The plant is part of the Apiaceae family, which includes well-known vegetables and herbs like parsley, carrot, parsnip and coriander.
Giant hogweed can be found in woodland (Image: Getty/DERO2084) Giant hogweed was introduced to Britain and Europe in the 19th century, from the Caucasus Mountains.
The earliest documented reference to the plant has been traced back to the Royal Botanic Gardens Kew Seed List of 1817, where seeds of the plant were listed.
The plant itself can reach over 10ft in height and, according to The Royal Horticultural Society (RHS): "Most gardeners will want to eradicate it, as it is potentially invasive and the sap can cause severe skin burns."
What does giant hogweed look like?
The Woodland Trust outlines the appearance of Giant Hogweed so that you can better identify the dangerous plant.
Stems: the stems are green with purple blotches and stiff, white hairs. The stems are hollow with ridges and a thick circle of hair at the base of each leaf stalk
Leaves: the leaves are huge, and can measure up to 1.5m wide and 3m long, and are often divided into smaller leaflets. The Woodland Trust compares them to rhubarb leaves, with irregular and jagged edges, with the underside of the leaf being described as hairy
Flowers: the flowers of the Giant Hogweed appear in June and July, and are small and white and appear in clusters on 'umbrella-like heads' that face upwards
Seeds: the seeds are dry, flattened and in an oval shape, almost 1cm long and tan in colour with brown lines
Jennifer Holmes, from Environment Controls, said: 'This dramatic-looking plant, found along many a river path, or woodland walk, must be treated with extreme caution.
'Its toxic sap contains furocoumarin, which makes skin extremely sensitive to sunlight and is a danger to humans and pets.
'Its distinctive flower heads emerge in June - and can be easily mistaken for other plants such as Cow parsley (non-toxic), Hemlock or Hemlock water dropwort (both highly toxic).
'If you touch giant hogweed, you may not notice anything immediately as the effects may take up to 24 hours to emerge, but soon large blisters will form on skin and will recur when exposed to sunlight.
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'As well as its harmful properties, as it colonises river banks this can make it difficult to eradicate - do not try to remove it yourself, always consult an expert.'
What should you do if you have a reaction to giant hogweed?
If you or your pet comes into contact with giant hogweed sap, immediately wash the affected area thoroughly with soap and cold water.
Crucially, keep the affected skin out of direct sunlight for at least 48 hours.
Seek immediate medical attention if blisters develop, and particularly if sap gets into the eyes.