Giant hogweed (Hercules perennial) • Dangerous skin reaction!

Author * in: Monika Preuk, medical author
Last update: June 03, 2022

Again and again – especially in social media – warned of the poisonous giant hogweed. Not only can contact with the up to four meter high plant lead to severe allergies. When giant hogweed is in bloom, just being close to the gigantic perennial can cause shortness of breath. We answer the most important questions about giant hogweed, allergic reactions, reporting requirements and control here.

Giant hogweed (also Hercules perennial) is not an inconspicuous poisonous plant along the way, but a gigantic herb with thick stems and large inflorescences. Who Giant Hogweed (botanical names: Heracleum giganteum or Heracleum mantegazzianum) and puts it in the floor vase at home as an impressive eye-catcher, but you put yourself in great danger: all parts of the plant contain toxins, especially so-called furocoumarins. These substances develop their destructive effect only under the influence of UV light from the sun.

At a glance:

Giant Hogweed: These burns threaten on contact

Recognize giant hogweed – profile of a poisonous plant

The umbelliferae come from the Caucasus and are considered a so-called neophyte. The designation means that this plant has immigrated and is displacing native plants (invasive species).

Because the perennial plant, which can be up to three years old, circulates up to 50,000 seeds with its flower. Giant hogweed seeds have excellent flight and swimming properties. Giant hogweed has spread rapidly in Germany in recent years. It grows at the edge of the forest, on rivers and streams, next to roads, on railway lines and in meadows. How to recognize giant hogweed:

  • Densely hairy stem with red spots

  • Stem has a diameter of up to ten centimeters at the bottom

  • Leaves are about a meter long and in three to nine parts, similar to rhubarb leaves but with a jagged edge

  • Flower umbels reach a diameter of up to 50 centimeters

  • The small individual flowers are white

  • heyday from Riesenhogweed: June to September

Caution: Giant Bear Claw is very resilient. Even if you mow it down, the root will sprout again within weeks.

There are also native species of hogweed, such as the much smaller meadow hogweed and mountain hogweed. Both varieties are also poisonous, but not quite as aggressive as the giant hogweed.

Burns, allergies: giant hogweed is so dangerous

Touching the beautiful flowers or just walking past the giant hogweed with a covered arm or leg can endanger your health: A few hours later, but even days later, mild to severe skin reactions occur. The toxins can penetrate textiles such as clothing. Local symptoms appear as

  • skin redness,
  • Itching,
  • fire blows up to
  • very extensive burn blisters as in burns 3. Degrees, i.e. particularly severe, poorly healing skin damage.

During flowering, the giant hogweed also releases its toxins into the surrounding air. Those who inhale them can experience shortness of breath and develop persistent, allergic bronchitis.

In addition, systemic signs are possible that affect the whole body and circulatory system. This happens, for example, when the skin reaction is very pronounced. Possible are:

Phototoxic skin reaction: why is giant hogweed so dangerous?

All Bärenklau species contain essential oils and so-called furanocoumarins (short form: furocoumarin). These are phototoxins. They only become toxic under the influence of sunlight. The principle works like this: You have contact with Riesenbärenklau. It doesn’t hurt at all. Only when UV light hits the skin area into which some plant sap has penetrated do these toxins combine with endogenous proteins and a strong allergic reaction reaction occurs.

This also explains why no symptoms appear immediately after contact with giant hogweed, but only hours later when the skin has been exposed to the sun. The medical term for this condition is light or photodermatosis. This is also known for sun allergies or Mallorca acne.

Attention: All parts of the plant of the giant hogweed contain the toxic furanocoumarins, especially the plant sap.

First aid after contact with Riesenbärenklau

Children and people who already suffer from allergies with skin reactions are particularly at risk. After contact with Riesenbärenklau, the following tips are useful:

  • Wash the affected area of ​​skin thoroughly under running water and with some alcohol ab.
  • Apply sunscreen with a high SPF and avoid exposing the skin area to the sun for the next few days.
  • If you have the slightest sign of a reaction, you should see a doctor as soon as possible.
  • If you have had contact with the hogweed in the area of ​​the eyes, mouth and face in general, you should definitely seek medical treatment.

Treatment and prognosis of skin damage caused by giant hogweed

As with other allergic skin reactions, giant hogweed damage becomes antiallergic medication prescribed, such as locally acting ointments and systemically acting tablets. In the case of severe damage, cortisone and other anti-inflammatory agents are useful. Nevertheless, the skin damage often heals only with great difficulty and very slowly. Pronounced scars and altered pigmentation often remain, as is also possible after burn injuries.

Is there a reporting requirement for Riesenbärenklau?

Due to the unpredictable danger of giant hogweed, it would only be understandable that the poisonous plant should be reported and destroyed. However, there is no obligation to report giant hogweed. The Federal Nature Conservation Act applies to public areas. The employees of building yards, city gardening and nature conservation associations are trying to prevent the giant hogweed from spreading.

However, if the plant grows on your own property, the owner is responsible. As part of the so-called hazard prevention measures, he*she should ensure that the Riesenbärenklau is thoroughly destroyed. However, fighting it is not easy. For one thing, cutting it off is dangerous because it involves direct contact with the plant. On the other hand, the Riesenbärenklau is a survivor. Even flowers that have been cut off can still form seeds, and parts of the roots that are disposed of in the compost form new emergency flowers with lots of seeds.

Professional companies are destroying extensive fields of giant Hogweed with special chemicals that require permits. The roots of the poisonous plant are then cut off and dug up. Regular mowing, tilling and mulching will help in the following years to ensure that no seeds left in the soil will sprout.

Ten tips to safely combat giant hogweed

Hobby gardeners should inquire at the local nature conservation association or the city garden center. The best time to control giant hogweed is in the spring, before the perennial has set seeds, or in the fall, after the flowers have faded. But even later in the year, the poisonous plant can still be eradicated.

In addition, the following tips help to get rid of giant hogweed forever:

  1. It is best to use a cloudy day or the evening hours to fight the giant hogweed. Then the plant sends hardly any furocoumarins into the air.

  2. Wear safety goggles, face protection, respiratory protection, long-sleeved clothing, long trousers and sturdy gloves – or a thick body protection one-piece suit. You should destroy this protective clothing after use because toxins could stick to it.

  3. What you also need: spade, secateurs and thick plastic bags to dispose of the plant parts.

  4. During the flowering period: Now cut off the flower umbels directly under the main umbel, i.e. under the point where the flower umbels split into several stalks.

  5. Disassemble the umbels and dispose of them in tear-resistant bags so that no more seeds can spread afterwards.

  6. Now dig up the turnip-shaped root of the giant hogweed or cut off the root under the so-called vegetation cone. This is the upper root area, which grows about 20 centimeters into the soil. Once this is removed, the root cannot grow again.

  7. Dispose of all parts of the plant in the household waste in tear-resistant bags. The packaging prevents the giant hogweed from spreading again.

  8. No part of the Riesenbärenklau may end up in the compost. There the plant would grow again.

  9. After the control action, clean all tools thoroughly with spirit and wear protective clothing, safety goggles and respiratory protection.

  10. Regularly check the places where the giant hogweed has grown. Because from the seeds that may have gotten into the ground, a new giant hogweed perennial can still grow after ten years. That is how long the seeds remain germinable.

Poisonous plants in the garden: These species are dangerous

Source: Lifeline | Das Gesundheitsportal by

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