Is Common Hogweed Poisonous?

2020 update: the following is a quote of mine that I use when teaching people who come on my foraging courses. It brings a smile and helps people to understand the hogweeds.

“The difference between common and giant hogweed is like going to the pub on a night out. Giant hogweed is the drunk, aggressive, muscular guy on steroids. He’s all pumped up and itching for a fight. Just brush against him, not even spilling his drink, and he will attack you viciously. Common hogweed, on the other hand, is the quiet, wiry, calm guy at the end of the bar. Brush against him, even spill his pint, and he’ll accept your apology and carry on with his pint. But if you try to wipe out his entire family with a huge killing machine, then you’re in trouble!”

Main article: June 2015

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 any contact with its sap will 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 however it’s important to be aware of the conditions when it isn’t safe.


There are reports of people using a strimmer to cut common hogweed 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.

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 personally known anyone have a hogweed allergy. It also has a long medicinal use in mainland Europe.  I have picked it when young (without gloves) and eaten it for years: leaf shoots, flower buds, use the seeds as a spice and the root as a tincture and flavouring 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 Umbellifer in the Apiaceae family – is the leading cause of food allergy in Europe. So I have spent some time reading the research on celery and parsnip allergies, psoralen, furanocoumarins and other exciting stuff. Here are my thoughts based on the research papers I have read.

The plant biochemical laboratory

Furanocoumarins (also called furocoumarins) are the biochemicals made by plants in the Apiaceae ‘celery family’ mainly to protect themselves from attack by fungus pathogens. High concentrations are responsible for phytotoxicity. They are most concentrated in the plant’s roots and fruits. In the green parts, psoralen (the parent compound of furanocoumarins) 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.

It is these toxins that induce phytophotodermatitis, irritating the skin of susceptible people and causing blisters with exposure to ultraviolet (UV) radiation in the UV-A range. The furanocoumarins are changed temporarily into a high-energy state when they absorb photons from the sunlight. They then release this energy into the skin where it causes damage to DNA in the skin’s epidermis, causing skin cell death. Sweating, wet skin, and high humidity increase the intensity of phototoxic reactions by increasing the skin’s absorption of the furanocoumarin.

What causes high furanocoumarin levels?

In some plants, like giant hogweed, furanocoumarin chemicals are always high as a form of defence. In plants like celery and common hogweed the levels can vary. If the levels rise, then problems occur for humans. So what causes high levels of furanocoumarins?

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 fungi, 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). Here is a report of celery handlers who had reactions to celery that was infected with the white mold fungus Sclerotinia sclerotiorum. 

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). Here is a report of phototoxic reactions while celery handling.

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 is really like a classic celery allergy being found in people not necessarily 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, there are a lot of the problems with celery nowadays (a 4 fold increase in the last 20 years). If it was introduced now as a novel food, I’m quite sure it wouldn’t be allowed on the market! One reason for the increase is that, by selectively breeding the plants to be more resistant to insects and 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 oral allergy syndrome 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. This is borne out by the clinical report of a woman who ate a large amount of celery root before using a sun bed. A comment on this case calculated that 22.5 mg of psoralens were in the 450g portion of celery root she ate.

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.

Cross breeding?

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 parsnip 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

Important! Wear full 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! You will also be more likely to suffer if you have been sweating and if it is sunny.

Basically when we launch an attack on the plant, the plant fights back to protect itself. They often ‘know’ we are coming. All plants are connected by fungal mycelium in the soil which like ‘Nature’s internet’ transports chemical signals to other plants. Some plants also give off pheromones (scent chemicals) which can signal distress – birch trees, for example, release methyl salicylate when attacked by aphids and other birches ‘smell’ this and start to produce defensive chemicals. So once the first hogweed plant has been strimmed it is likely that the rest of those in the hedgerow sense the danger, and will start to increase their furanocoumarin levels before you even get there! So as with any fight, put on your armour before going into battle and wear protective clothing and goggles. Even strimming nettles can result in minor burn spots with semi-permanent staining.

Update April 2017: I received an email from someone who’d been out with a strimmer and says “I volunteer with the National Trust and two weeks ago I was strimming an orchard with common hogweed. I was wearing protective clothing and a head helmet with a grill guard. Two days later I was sunning myself on the beach and my neck became very inflamed (like the picture of the lady who squeezed citrus fruit in your article). I reported what happened to the rangers the next week, and they were very aware of the symptoms and warned all the volunteers to protect their necks from spraying sap from hogweed strimming and to wear a full face guard. They also said I should immediately apply water to the affected areas to avoid skin burns. So maybe there should be more warnings out there to prevent others getting the burns. The rangers said the burn marks last for some considerable time. I’m applying hydrocortisone creame twice a day which seems to be helping.”

I advise: A) full protective clothing if you’re going to strim any hedgerow. Cow parsley, wild parsnip and even wild fennel have been reported as causing burns. B) if exposed, wash with soap and cold water to ensure all the sap is removed. C) Keep out of the sun for several days afterwards. D) if you are a ranger or employer do make sure that any one strimming for you should be provided with information and full protective clothing when using a strimmer. E) a scythe with a ditch blade is much safer than a strimmer as plants are not pulverised with sap flying everywhere, and just as effective and easy to use if kept sharp. 

If you attack a cornered wild animal you’d expect to get bitten, don’t forget that plants can’t move and some will also ‘bite back’. 

Personally speaking…

I will continue to eat common hogweed and teach responsible harvesting until celery, parsley and parsnips are banned from sale. But if you have a celery allergy or use sun beds I’d advise you not to eat or handle hogweed. And don’t eat it in excessive amounts, especially if you’ve been spending a lot of time in the sun!

Here is an interesting study on the effect of different quantities of celery eaten and the effects. It showed that the phytophototoxic threshold dose is not reached by the consumption of celery roots and other conventional vegetables under normal dietary habits. So as with most things, everything in moderation.


Other hogweedy posts:
Delicious hogweed tempura
Common Hogweed: A taste like no other
Edible wild spice conversion chart
Spiced Chaga and Elderberry Tea

============================

Allergy Update: June 2016

I recently heard from Eric Biggane who is also a foraging teacher. Eric says “I’ve been picking [common hogweed] without gloves since childhood and never reacted to it until about ten years ago. Now if I brush past the plant at any time of year my hands come up in itchy painful blisters that a week later cause my hands to dry out and crack to the point of bleeding. This reaction happens in the same places regardless of where my skin contacted the plant. I’ve seen several skin specialists who deny that I’m allergic to anything and give up looking. Please don’t think I’m in any way criticising your excellent website, what made me write to you was you mentioned in it the effect might be accumulative and that has got me thinking as I was fine years ago. I used to work on a farm and harvested celery by hand, sometimes I would have a mild reaction to the sap, maybe that didn’t help. I’m always cautious when I teach people about hogweed but I always feel like it’s putting people off, as I said I’m the only person I’ve ever met who has a reaction to the stuff. If you know of anybody else who reacts, please let me know as I would love to talk to them as it quite a severe reaction.”

As allergies can be accumulative it is quite possible that his early reactions to picking celery sensitised him and is causing contact dermatitis when he handles hogweed.

Interestingly, I have a friend who took up juicing. He liked the apple, carrot and celery combination and instead of varying different juices throughout the day, he drank only this combination for about a month. He was juicing two heads of celery, a bag of apples and a bag of carrot and drinking it daily. After about a month, when the summer arrived, he started to get dark pigmented patches on his face. They reminded me of the melasma experienced by some women as a hormonal change. As his health was otherwise good, we could only put it down to a phytophotodermatitis reaction to ‘overdosing’ on celery juice (although perhaps it was the carrots?). For the last two years, in the summer as soon as his skin starts to tan, the patches reappear in exactly the same place, although, in his case, this is not accompanied by any itching or pain. So the compounds in celery juice can certainly start a phytophotodermatitis reaction.

Phototoxicity in limes and citrus fruits

There are also documented cases that dark, pigmented facial burns can also happen from ingesting too much citrus fruit when also in contact with sunshine. Here is also a case of a woman who developed lesions several hours after she had baked a key lime pie from scratch. Part of the preparation included squeezing fresh limes by hand; afterwards, she walked outside on a bright, sunny day. The picture below shows the burns she experienced.

Phototoxic reaction to limes and sunlight

Bartenders who make cocktails and chefs who squeeze limes and lemons should be aware of this and avoid going out in the sunshine after handling a lot of citrus.

While grapefruit juice also contains furanocoumarins it seems that they are weaker and of low concern. It seems that the coumarin derivative limettin present in limes is to blame.

Parsnip, celeriac and carrot allergies

Parsnips can also be problematic as they too contain furanocoumarins but again, it seems to be all in the amount eaten and the exposure to sunlight, as a 200g portion of parsnip seems to be under the threshold. Some people also experience contact sensitivity to carrot, parsnip and celeriac, all members of the Apiaceae family.

Heracleum maximum (prev. H. lanatum) known as cow parsnip in North America can give the same type of burns as giant hogweed. It is, confusingly, occasionally also called ‘hogweed’ although it is not the same species as the British common hogweed but closely related. Here is the case of an 11 year old boy in Alaska who experienced burns after coming in contact with H. lanatum.

Every now and then there are reports of contact dermatitis caused by carrots too Report 1. Report 2. and another common Apiaceae herb, a parsley reaction in a boy and phytophotodermatitis in pigs exposed to parsley. Carrots and parsley are also related to celery and hogweed.

As even the most innocuous foods, not just in the Apiaceae family, such as the humble lettuce can cause allergies, it is sensible when trying a new food always to try a small amount first.

29 Comments

  1. I have just been burned through my protective trousers and T-shirt from strimming hogweed. The burns are just as bad as on my exposed arms!

  2. Back in the Summer of 2014 I was working on an Estate on the Isle of Mull. I was strimming and happened to hit a clump of Common Hogweed. Of course it was quite hot and sticky so by this point I had taken off my longsleeved top, and the helmet and visor didn’t happen to have the cloth neckguard fitted. I got splattered. Instantly knowing I was in trouble I rushed to the nearest water point and washed off as best I could, but by this point the damage had been done. Over the next few hours (and following days) the skin on 3/4 of my arms and around my neck/clavicle broke out in dozens of 5 pence coin (and smaller) burn blisters. Thankfully because I was able to wash it off fairly quickly the burns were not terrible, or particularly painful – though it did take nearly two years for the marks to fade away. I have no recurring photosensitivity in those areas thankfully.

    • A lucky escape! Thanks for sharing that. I wish the estates would invest in good scythes. I use one instead of a strimmer and it takes out the hogweed cleanly without a splatter.

  3. Brilliant article on Common Hogweed the best I’ve ever come across. I have a paddock full of it and it burnt my horses on any white pigment areas they had.
    Had to detox them using Milk Thistle but since found a supplement that was a lot stronger and helped heal o e of the horses who took ages to heal.

    Please may I share this article in the horse community?

    Thank you

  4. Mohammed Zaman

    Fairy liquid washing up liquid always works for me. Istant neutralise the hoqweeds poison in secounds.

  5. lorraine

    i was cutting common hog weed with my bare hands and putting on my horses track for them to self-select, however my right hand has felt slightly weak since doing this and a bit sore I think it could be a reaction to the hog weed so will definitely wear gloves in future.

  6. warthog watts

    Fantastic article thank you. I have common hog weed In our somewhat neglected garden and have cleared it with loppers when young but one plant has suddenly burgeoned and is going to need removal so I was checking how careful I needed to be. I will now be cautious with it.

    • I’ve never had problems picking or lopping but best to take care. It’s the strimming that seems particularly bad and where they are in quantity.

  7. Stephen Glover

    Hello. I’ve been a hunter gatherer for about 44 years now, and I remember my father giving me advice. – He said, “Eat a very tiny piece of every plant available in your environment.” For myself, this has worked, so far! I wouldn’t expect anyone else to do this, unless they gain a knowledge of each of these plants – and I mean some fairly mean chemistry! Obviously, some plants such as Monkshood are to be excluded, as are a few of the fungi’s. Perhaps I am very lucky, or my constitution is strange! – I would say that if a person moves to a different part of the country to be aware of the fact that plant chemistry can vary quite a large degree. Try to be aware of your environment, as 9 out of 10 folks who ask me what I am foraging for have no idea as to the name of the plant and have no knowledge of what herbs are edible and what are not… I had the benefit of folks who knew these things and were willing to explain to the 9 year old, interested me! If you don’t know what it is, don’t touch it. Take a photograph and use the internet to find a local person who has knowledge of these things… Blessings, And be careful, and you will be fine. Regards. Steve.

  8. Nigel Appleton

    Strimming last Thursday on a very warm and very sunny day. With no knowledge of the potential issues I strimmed an area of common hogweed. I was not wearing a shirt!! Now covered in dark red marks. Some blistering.
    This is a dangerous plant if not handled correctly.
    Dreading how long I will be affected. 4 days on rash is, if anything, getting worse.

    • I’m so sorry to hear that. Keep right out of the sun now and use neat aloe vera gel or plenty of fresh dock gel (from the base of the plant).

  9. Patrick Mcdermott

    I was strimming a fence line to put electric fencing up for the 2 ponies we planned to graze in a field we started renting.
    This was last week in the lovely sunshine…so shirt off unfortunately.
    Knew nothing about this problem so the next day when I had loads of small red patches with small blisters start appearing along my chest I sent the pics to my GP.
    He diagnosed mild shingles!
    Today… (3 days later) we discovered the ponies have very sore patches , with blisters on the white patches around their nose and mouths.
    After much googling I came across this site…very helpful and explains a few things…many thanks.
    while I am relieved I probably don’t have shingles, I wonder if we have a bigger problem with the ponies.
    They have probably eaten the loose shredded bits of plant I strimmed by now and the rest of the large field will only have the untouched plants remaining….i.e the damage will already have been done.
    What’s best to alleviate the pain for the ponies and would they be OK with the rest of the field….or do we pull them out?
    Any advice would be gratefully received.

    • I have deer and rabbits passing through my garden that regularly nibble on the common hogweed shoots. But then I don’t strim it so it’s not ‘armed’. I suspect that the ponies ate what you had strimmed or nibbled the stumps that you’d strimmed. The rest of the plants in the field, once they’ve calmed down, should probably be ok unless the ponies have become sensitised to it now. I would suggest dock leaf gel (from the base of the dock plants) on the blisters if they can’t lick it off. If they can, make a tea from plantain leaves and add it to their drinking water. Water from boiled oats is also soothing.

    • If you feel the need to do more cutting I highly recommend a scythe with an Austrian ditch blade. Simon Fairlie scythes are excellent just google his name. Kept sharp, they go through hogweed, thistle and dock with one easy slice and avoid the massive chemical reaction caused by full mechanical onslaught. Aside from that they don’t need petrol, don’t smell or make a noise, are extremely good exercise and allow the grasses and wildflowers to grow through. Using a scythe will positively transform a meadow habitat in a way that a strimmer never does.

  10. Michael Amos

    I am very confused now and a bit worried. I have found that we have lots of common hogweed growing on our two allotments . When I first looked it up people were saying it is safe and you can touch it with your bare hands and eat it etc and now I see people saying they are getting bad burns from it . My worry is that I do lots of weeding by pulling up lots of weeds with my bare hands and if there are many young common hogweeds there then it will probably get me sooner or later . Also my partner loves strimming everywhere too so I am worried about her . Also I am confused as to whether common hogweed is exactly the same plant as cow parsnip . I read one article saying they are the same then in another article it gave them different Latin names , the last part . All very confusing . I wish I was an expert in these matters instead of a novice .

    • In the USA there is a species of hogweed (Heracleum lanatum) often referred to as cow parsnip hence sometimes people erroneously use that name here. It is not a species found in the U.K. We do have a wild parsnip here (Pastinaca sativa) that can cause burns. It is different to our common hogweed (Heracleum sphondylium) and different to giant hogweed (Heracleum mantegazzianum). I have never got a burn from picking common hogweed with my bare hands and I eat a lot of it! However, if you have a lot of people around you strimming and using herbicide sprays, then your common hogweed may well be ‘armed’ with self-defense chemicals while that is going on. You could give your partner a scythe for her birthday: selective weed control, no petrol odour, no antisocial noise, great exercise and doesn’t smash plants into such tiny pieces that they are forced to defend themselves. (Google Simon Fairlie scythes, Austrian ditch blade for weeds). You could also persuade everyone in the allotments to go organic: benefits people, planet and plants. If not, wear gloves.

      • I live in a residential neighbourhood in Canada. There is a house one street over that has what looks like common hogweed in the front garden. It is over 6 feet tall and is close to the sidewalk. There are lots of children in the neighbourhood. Should we be concerned?

        • If it was in the UK and over 6 feet tall I would expect it to be giant hogweed. Have a good look at it for red blotches on the stem or crystal spikes. If it is giant hogweed it would be worth trying to speak to the property owner about it. I once found it growing in a supermarket car park right next to a pedestrian crossing. I had to complain a couple of times but eventually they removed it. If it is common hogweed it is unlikely to hurt anyone just from brushing against it.

  11. The point about Fairy Liquid being used is a good one probably with scientific basis. Furocoumarins are fat soluble chemicals so they penetrate the outer layers of skin to live epidermis quite easily.

    Then under UV light they are already present in the excited state to bond with RNA and DNA in skin cells very quickly.

    My guess is using a concentrated detergent/soap with extract some of these furocoumarins back from your skin into the detergent and reduce the photodermatitis.

  12. I grow aloe vera plants on m window will to treat hogweed burns. I just pluck off a juicy leaf and squeeze it on to the burn area and in an hour there is no pain or blistering just a red mark. Its brilliant!

  13. Brychan Roberts

    Excellent article the best that I have come across on this subject which is really important given that common hogweed is just everywhere. I have two questions and it would be very helpful if you were able to answer them please.

    The furanocoumarin if present for example on clothing does its efficacy to do damage decline over time and effectively become neutralised ?
    Also if on clothing will a standard wash with non bio detergent remove the furanocoumarin and make it safe ?

    Thank you.

    • Clothing can be washed and, although I haven’t tested it, I would assume that furanocoumarins decline over time as most ‘attack chemicals’ do.

  14. Anne Devereux Hemmings

    What a fantastically detailed article! Very informative-I saw a large hogweed plant today which was Common Hogweed and was telling another walker about my horrible experience with Giant Hogweed in France-large fluid filled painful burn blisters on my knees for ages My brother had just scythed his field and I knelt on stalks in the dark while bashing in tent pegs-it was very hot sunny weather. …

What do you think?

This site uses Akismet to reduce spam. Learn how your comment data is processed.