• Giant Hogweed (Heracleum mantegazzianum) is an ornamental flower originally introduced from Asia. It is a plant that reaches heights of 10 to 15 feet in height. Numerous white flowers, clustered in an umbrella-shaped head, bloom from early spring through late summer
  • other than in size, the Giant Hogweed bears a close resemblance to Cow Parsley and Hogweed
  • Giant Hogweed has a reddish purple stem and spotted leaf stalks, with fine spines that make it appear furry
• Giant hogweed was brought to the UK by Victorian explorers who took the seeds back to Kew Gardens, London, to plant. Later, seeds were obtained by various people who wished to have the plant in their country gardens. However, the plants spread from their original planting sites and since the numbers of Giant Hogweeds has been steadily increasing since.
  • the plant is now common in the UK and is associated with both occupational health and environmental problems
  • common sites for Giant Hogweed include along roads, footpaths and railway lines, rivers, wasteland, demolition sites and in agricultural areas
• contact with the intact plant is not harmful. Contact with the sap occurs through brushing against the bristles on the stem (as with a stinging nettle) or breaking the stem/leaves - exposure to the sap will elicit a phytophotodermatitis (a photodermatitis secondary to psoralens produced by plants)
  • sap contains a toxic glucoside called furocoumarin - this makes the skin sensitive to natural or artificial light
  • sap contact with moist skin, followed by exposure to light, results in the eruption of painful burning blisters on exposed areas within 48 hours
  • phytophotodermatitis may be confused with other skin conditions such as allergic dermatitis and impetigo
    • the photodermatitis progresses aggressively and may be also be mistaken for a resistant staphylococcal infection or necrotizing fascitis (1)
  • in the event of contact with the sap of this plant, the skin should be covered to reduce the exposure to sunlight and washed IMMEDIATELY and thoroughly with soap and water
  • if phytophotodermatitis develops then treatment is supportive
    • oral antihistamines
    • analgesia
    • topical calamine
    • topical steroids
    • if secondary infection is suspected then antibiotic treatment
    • systemic steroids may be beneficial (1) - consult expert advice

For information about Giant Hogweed from UK environmental agencies click here

Reference:

1. Langley DM, Criddle DM. A 43-year-old woman with painful, vesicular lesions from giant hogweed photodermatitis. J Emerg Nurs. 2006 Jun;32(3):246-8