Aug 2022

Is Giant Hogweed ( Heracleum mantegazzianum) poisonous to humans?


In a word, yes. This particular invasive weed species to the UK (originally native to Central Asia) can cause some nasty burns and even blistering, but what is not very well known is that it will continue to cause severe blistering in the following season and sometimes the season afterwards. That is, let’s say you touched it in 2022 and had blistering, unless you cover your skin up, even though you do not touch it in 2023, you will also have blistering in 2023 and sometimes even in 2024.but what makes (Heracleum mantegazzianum) Giant Hogweed Poisonous?


Giant Hogweed sap and phototoxicity


The sap of the Giant Hogweed plant can produce a mild rash to watery blisters and possible chronic dermatitis, all of which may require hospital treatment. It prevents the skin from protecting itself from sunlight which leads to a very bad sunburn. 


The Giant Hogweed sap contains a family of compounds known as furanocoumarins (referred to as furocoumarins), it’s these photosensitizing furanocoumarins, on contact with human skin in conjunction with sunlight, that can cause phytophotodermatitis.


Giant hogweed plant


These compounds are found throughout the entire plant: the flowers, the stems, the roots and seeds. The most concentration of the sap can be found in the leaves.


The phototoxic effects of the sap’s compounds are due to their interaction with DNA when they absorb UV light of a specific wavelength. UV radiation with a wavelength between 320-380 nanometres can trigger the effects of furanocoumarins.


Furanocoumarins interact with the bases that help hold DNA strands together and ultimately this can cause cell death and results in the characteristic skin reddening and blisters.


Safety Precautions and the need for protective clothing


The correct type of protective clothing should be worn when handling Giant Hogweed due to its potentially dangerous effects on human skin. It is important to consider that absorbent fabrics can soak up sap and allow the transfer of sap onto skin and cotton and linen fibers can be penetrated by plant hairs.


  • Prevent UV sunlight from reaching skin by wearing long waterproof gloves, long sleeves, pants, boots, and eye protection.; synthetic water-resistant materials.
  • Do not touch the plant with bare skin.
  • Apply sunblock before beginning work.
  • Do not touch your face or rub your eyes if there is a chance you have any sap on your hands or the outside of your protective clothing.
  • Do not use a “weed-whacker” or brush cutter as sap may splatter as stems are cut and can splash three to four feet.
  • Launder clothes that may have contacted plants.
  • Wash equipment with water immediately after use.


How to treat exposure to Giant Hogweed Sap on skin or eyes


It’s advisable to seek medical treatment if any skin inflammation subsequently occurs from contact with Giant Hogweed.


Giant Hogweed leaves contain more sap in June and the concentration of the active compounds will vary between plants. 


Initial exposure to the sap is completely painless and the reaction is activated by ultraviolet radiation which can begin 15 minutes after contact and will peak 30 minutes to 2 hours after exposure. Heat and moisture (sweat or dew) can worsen the skin reaction.


When coming into contact with Giant hogweed sap, wash the affected area thoroughly with soap and water immediately and keep the exposed area out of sunlight for 48 hours. If sap goes in your eyes, rinse them with water and wear sunglasses.


If a reaction has occurred, the area of skin may be sensitive to sunlight for a few years and you may want to apply sunblock or keep the affected area covered from the sun when possible.


Should you become exposed or if reactions do occur then seek medical attention.


Giant Hogweed UK Hotspots Map


There has been rapid spread of Giant Hogweed across the UK despite the implementation of control measures.

The Botanical Society of Britain and Ireland’s database provides access to the millions of botanical records collated by the society. The data is used to generate the distribution maps is available for academic research and other specialist uses from the BSBI’s network of county recorders, local groups and taxonomic experts. Here is the UK Giant Hogweed Hotspot map.


What not to do with Giant Hogweed


In the UK it is illegal to plant or facilitate the spread of Giant Hogweed and councils take active measures to remove it when its presence is reported. Increasing numbers of articles citing cases of Giant Hogweed burns have been appearing in recent years.


Giant Hogweed is listed on Schedule 9 of the Wildlife and Countryside Act (1981), the same as Japanese Knotweed (Reynoutria japonica) and so is one of the listed non-native invasive species, which requires the landowner to prevent the spread beyond the boundaries of the property into neighbouring land.


Don’t whack, smash or cut the stems of the Giant Hogweed as the sap may splash on unprotected areas of yours or others skin.




Contact a professional service to treat and dispose of the invasive weed safely if it has been identified.





National Library of Medicine

NHS Highlands

Compound Chem – Explorations of everyday chemical compounds

Botanical Society of Britain and Ireland – UK Hotspot map




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Japanese Knotweed
Giant Hogweed
Himalayan Balsam
Hemlock Water Dropwort