Summer is the time when outdoor work and leisure activities increase. It is also the season when plants like giant hogweed grow and bloom most. Direct contact with this beautiful umbrella plant, however, leads to serious skin lesions and skin burns that often necessitates a visit to the emergency room.
Have you ever heard of the giant hogweed?
The giant hogweed is an extremely toxic exotic plant particularly present in the British popular culture. It is also mentioned in the 1971 studio album entitled “Nursery Cryme” by the English rock band Genesis where the eternal struggle between this exotic plant and the English authorities trying to eradicate it is (humorously) narrated. Historically this plant was rediscovered in 1895 by two Italian doctors: Emile Levier and Carlo Pietro Stefano Sommier, to which they gave the botanical name of Heracleum mantegazzanium, in honour of their friend and physician Paolo Mantegazza, the first popularizer of Darwin’s scientific theories in Italy.
How can you recognize giant hogweed?
Giant hogweed, also known as Heracleum mantegazzianum, is considered to be the largest and most beautiful umbrella plant in the world; it can reach a height of over 3 meters. It is recognizable due to the colour of its leaves, which are a bright light green colour tending towards yellow with deep lobes and segmentations. The trunk is very thick and robust, similar to that of artichoke, with dark red streaks and surrounded by spiky hairs. The diameter of the umbrella makes it the largest among the umbrella plants.
The fruits have an ovoid appearance, and at the moment of flowering, their envelopes remain attached to the base of the umbrella and subsequently tend to wither. Giant hogweed blooms from early spring until late summer, especially in the vicinity of wetlands (streams or canal banks). These characteristics differentiate it from the garden angelica (Angelica archangelica) and the common hogweed (Heracleum sphondylium).
Who is most at risk of coming across giant hogweed?
Gardeners, trekkers, forest workers, and people who work outdoors in wooded or undergrowth areas where giant hogweed is present are most at risk of injury caused by giant hogweed.
How is giant hogweed sap toxic?
The sap of giant hogweed contains different photoactive agents called furocoumarins, of which the most predominant is 5-MOP (5-methoxypsoralen). Injuries are caused when these photoactive agents are exposed to and activated by UV-A rays present in sunlight. This gives rise to a toxic process in which the furan ring of the photoactive agent is cross-linked with the pyrimidine bases of DNA in the patient’s skin, thus causing an increase in oxidative stress leading to cell membrane damage and subsequent inflammation and oedema. The culmination of these processes leads to the development of phytophotodermatitis (PPD).
Similar to other plants capable of phototoxicity, skin damage is dependent on certain factors such as:
- The concentration of the phototoxic agent
- During summer months, levels of phototoxic agents are higher. Moreover, they are more concentrated in fruit, present in intermediate levels in the leaves, and are minimally present in the stem.
- The thickness of the skin
- Damage is more extensive and deeper in the skin that is thinner.
- Sun exposure
- When sun exposure is prolonged, there is greater photoactivation and therefore greater damage.
- Skin moisture
- Sweat or dew that may be present on the skin can accelerate the toxicity process.
What are its symptoms?
Symptoms of giant hogweed exposure usually involve an erythematous lesion accompanied by extremely intense pain. If not treated early, erythematous lesions evolve into burns with the appearance of one or more liquid-filled vesicles. Generally, patients may have fatigue and slight tachycardia, but vital signs and laboratory test may be normal.
During the history and physical examination, staphylococcal infection, allergic dermatitis, purpura, impetigo, and fungal infection must be considered in the differential diagnosis.
Upon contact, the subject should immediately wash the red area abundantly, dry it, and cover it to avoid sun exposure. Other recommendations would include avoiding to take baths and showers and apply high protection sunscreen to the lesion.
If erythema appears, the use of sulfadiazine cream and analgesic anti-inflammatory drugs should be considered. Moreover, the use of ice to reduce inflammation can also be useful. In the event of an injury characterized by one or more blisters or loss of tissue, a conservative treatment consisting of cleansing with antiseptic solution (i.e. Clorexidine) and bandaging with synthetic microporous membranes have proven effective. In cases where the phototoxicity process has been prolonged enough to cause extensive and deep burns, skin grafting and surgical debridement are necessary.
In conclusion, the message for our patients who operate or live in areas where giant hogweed is present is to “look but absolutely don’t touch” this beautiful plant. Secondarily, it is also important to subsequently report its presence to public authorities; in fact, many countries or regions follow a specific eradication program for this plant which can prove dangerous for humans and animals.
References and Further Reading
 Heracleum mantegazzianum (giant hogweed) – Invasive Species Compendium – https://www.cabi.org/isc/datasheet/26911
 Derraik JG. Heracleum mantegazzianum and Toxicodendron succedaneum: plants of human health significance in New Zea-land and the National Pest Plant Accord. N Z Med J 2007;120: U2657.
 Marcos LA, Kahler R. Phytophotodermatitis. Int J Infect Dis 2015;9(July (38)):7–8.
 Pira E, Romano C, Sulotto F, et al. Heracleum mantegazzianum growth phases and furocoumarin content. Contact Derm 1989; 21:300e3.
 J Emerg Nurs. 2006 Jun;32(3):246-8. A 43-year-old woman with painful, vesicular lesions from giant hogweed photodermatitis. Langley DM(1), Criddle LM.
 Baker BG, Bedford J, Kanitkar S. Keeping pace with the media; Giant Hogweed burns – A case series and comprehensive review. Burns. 2017 Aug;43(5):933-938. DOI: 10.1016/j.burns.2016.10.018.
 Chan JC, Sullivan PJ, O’Sullivan MJ, Eadie PA. Full thickness burn caused by exposure to giant hogweed: delayed presentation, histological features and surgical management. J Plast Reconstr Aesthet Surg. 2011;64(1):128-130. doi:10.1016/j.bjps.2010.03.030
 Pfurtscheller K, Trop M. Phototoxic plant burns: report of a case and review of topical wound treatment in children. Pediatr Dermatol 2014;31:e156–9.