Common hogweed is not poisonous. It’s also not to be confused with giant hogweed which has very high levels of furanocoumarins in the sap, and contact with it can give you severe phototoxic burns. It is commonly confused and misreported and a Google search can result in a lot of erroneous information. By and large, common hogweed is safe and perfectly edible under ‘normal’ conditions.
There are reports of people using a strimmer who have experienced burns from triggering production of the irritating sap. I was also intrigued by my friend Robin Harford‘s report of another (his seventh) common hogweed allergic reaction reported to him in Devon. So I decided to look at the plant’s biochemistry and research literature to see under what conditions common hogweed could be dangerous, if at all.
I have 3 acres in Scotland dominated by hogweed and handle it a lot albeit with the respect that I handle all large plants. In all the years that I have taught foraging, I have never known anyone have a hogweed allergy. It also has a long medicinal use in mainland Europe. I have also eaten it for years: leaf shoots, flower buds, use the seeds as a spice and the root as a tincture and flavouring. Earlier this year it was served to 50 people at a dinner I attended and I know other people who eat it every year.
My friend Mark Williams, also a foraging tutor, says “I have now fed it (well fried, almost to caramelisation) to several hundred people with no adverse reactions reported. In fact I’ve had more people not get on with chanterelles than common hogweed. I did have one experienced forager at the weekend who declined to taste the seeds, having experienced some tingling in his mouth from tasting them in the past. I wonder if the effect may be cumulative in some people. I eat loads and haven’t developed any reaction”.
So is common hogweed actually dangerous?
Firstly, I do point out to people on my courses that any one can be allergic to anything and that celery – also an Umbillifer – is the leading cause of food allergy in Europe. So I have spent some time reading research on celery and parsnip allergies, furanocoumarins and other exciting stuff. Here are my thoughts based on the research papers I have read.
The plant biochemical laboratory
Furanocoumarins are the biochemicals made by plants in the Apiaceae ‘celery family’. High concentrations are responsible for phytotoxicity. They are most concentrated in the plant’s roots and fruits. In the green parts, psoralen has also been found to be most concentrated in the plant’s stem skin. There are quite a few different types:
- Roots > Bergapten, pimpinellin, isopimpinellin, sphodin.
- Fruits > Bergapten, isopimpinellin, phellopterin, xanthtoxin, heraclenin, imperatorin, byakangelikol, byangelicin)
What causes high furanocoumarin levels?
In some plants, like giant hogweed, furanocoumarin chemicals are always high as a form of defence. In plant’s like celery and common hogweed the levels can vary. If the levels rise, then problems occur for humans. So why causes furanocoumarin strength?
Psoralens are linear furanocoumarins that are believed to be the phytoalexins associated with Apiacae resistance to pathogens. Pathogens are microorganisms that cause disease or illness. They included bacterium and viruses like the carrot mosaic virus that is found in areas of intensive farming. (Carrots are also members of the Apiacae family.)
The phytoalexin response varies and increases, as a defence mechanism, when subjected to various environmental stress factors. These include fungal infection, copper sulphate (used in a lot of chemical sprays), UV light (England is certainly much sunnier than Scotland) and low temperatures. (For example, frozen parsnips have a much higher psoralen content than fresh parsnips).
Mechanical damage, that occurs during harvesting and storage, has also been shown to increase psoralen concentration by over 45 times. Celery allergies often develop in grocery workers who handle celery, especially celery that has been bred to be pathogen resistant (and therefore high in psoralens).
Celery allergy – Europe’s No 1 food allergy
Allergenic proteins associated with oral allergy syndrome (OAS) are usually destroyed by cooking. However this is not the case with celery, which may cause a reaction even after being cooked.
I believe that common hogweed allergy really is a classic celery allergy being found in people not usually experiencing a celery allergy. If the furanocoumarins in some of the common hogweed plants reach higher than normal levels – increased by UVA light, pathogen attack or mechanical damage – and exceed the levels found in shop-bought celery, then the allergy will be triggered.
Why are allergies on the increase?
Interestingly, a lot of the problems with celery nowadays (a 4 fold increase in the last 20 years). One reason is that, by selectively breeding the plants to be more resistant to insects as fungi, man has raised the furanocoumarin content in celery to levels which now trigger the allergy in people who didn’t get it before. There are studies comparing people handling different strains of celery which prove this perfectly.
Who is particularly susceptible?
Although anyone could theoretically get a phototoxic injury from sap high in furanocoumarins, during normal consumption of celery (and I believe common hogweed) only those with a celery species allergy or the predeterminant qualifying factors (family atopy, recent UVA exposure, 3 pollen sensitives, etc) are likely to ever experience OAS mouth symptoms.
People with allergies to alder, birch or mugwort pollen are more likely to become allergic to celery. Typically the sufferer is already likely to have experienced hay fever, asthma, allergies or eczema. with a family history of them also. Many people have no idea that they have OAS until swelling, tingling or pain develops while eating certain foods.
There is also evidence that there are more allergy and hay fever sufferers down south as the south experiences higher pollen counts and airborne pollutants.
Sun tans and psoralen don’t mix!
It has also be found in some studies, that people who have already recently been exposed to sunlight (tanning beds or sunny spells) can react to psoralens when they have not previously reacted to them before. It has also been found that people with fairer, less pigmented skin (e.g. Skin Type I and II) are more prone to reactions than those with dark, pigmented skin.
The plants in the south of the British Isles are exposed to more sunlight (and possibly a greater intensity of sunlight than in Scotland). Also people living in the south are more exposed to sunlight. So if you have just got yourself a sun tan, you can theoretically increase your chances of having a reaction.
So it is logical to assume that both the common hogweed plant is variable and the foraging person is variable. The former as to psoralen content, the latter as to a predisposition to allergy.
Heracleum, is a far wider genus than possibly suspected. The European invasive species with known phytophototoxicity include giant hogweed Heracleum mantegazzianum, Sosnowski’s hogweed Heracleum sosnowskyi (not yet recorded in UK) and Persian hogweed Heracleum persicum (possibly in the UK). (H. mantegazzianum is less shade tolerant than H. sosnowskyi.) Species of the genus Heracleum can hybridize causing confusing in species identification. There is also the possibility for some people of confusing the plant (before flowering) with Wild Parsnip Pastinaca saliva. The native European hogweeds are common hogweed Heracleum sphondylium and Siberian cow pasrnip Heracleum sibiricum and further to that there are at least eight known hybrids but without distribution detail:
- Heracleum sphondylium subsp. chloranthum (Borbás) Neumayer
- Heracleum sphondylium subsp. elegans (Crantz) Schübl. & G. Martens
- Heracleum sphondylium subsp. glabrum (Huth) Holub
- Heracleum sphondylium subsp. orsinii (Guss.) H. Neumayer
- Heracleum sphondylium subsp. pyrenaicum (Lam.) Bonnier & Layens
- Heracleum sphondylium subsp. sibiricum (L.) Simonk.
- Heracleum sphondylium subsp. sphondylium
- Heracleum sphondylium subsp. trachycarpum (Soják) Holub
Wear protective clothing when strimming
Common hogweed is variable in sap phototoxicity with the most cases of phytophototoxicity reports coming from people who have attacked it with a strimmer.
As you read earlier, mechanical damage causes a phytoalexin (furanocoumarin precursor) response triggering the production of phototoxic sap, so a strimmer is a fairly fatal device and will set off the production of furanocoumarins in double quick time!
Basically when we launch an attack on the plant, the plant fights back to protect itself. So as with any fight, put on your armour before going into battle. Even strimming nettles can result in minor burn spots with semi-permanent staining.
I will continue to eat common hogweed and teach responsible harvesting until celery and parsnips are banned from sale!
Other hogweedy posts:
Delicious hogweed tempura
Common Hogweed: A taste like no other
Edible wild spice conversion chart
Spiced Chaga and Elderberry Tea