15. October 2021
Late flowering plants still cause allergies in October

Is hay fever over after the summer? Unfortunately not. Late flowering plants such as ragweed can still cause hay fever symptoms well into October.

People with allergies in Germany are most likely to have heard of the late flowering plant Ambrosia artemisiifolia, or ragweed. No wonder: Ragweed pollen is one of the most common allergy triggers in autumn.


Ragweed is related to mugwort. People with a ragweed allergy therefore often react to mugwort or other types of ambrosia artemisiifolia, such as wormwood. Because ragweed is an aster, cross allergies with other asters, such as goldenrod or sunflowers, are also common.


As far as allergy symptoms are concerned, ragweed ticks all the boxes:

  • The main symptom is hay fever with typical signs such as itchy eyes, sneezing, runny nose and congestion.
  • Allergic asthma may occur as a result.
  • Ragweed pollen allergy can also lead to oral allergy syndrome. Components of ragweed pollen are very similar to certain proteins in foods. If these foods come into contact with the oral mucosa while eating, the body (mistakenly) produces an allergic reaction. These foods include apples, bananas, cucumbers, melons, carrots, potatoes, peppers, peaches, celery and zucchini.
  • If the skin comes into contact with the ragweed plant – for example, if you touch the plant without gloves – hives (contact urticaria) can occur.


Who is affected by this allergy?

In Germany, ragweed has been documented as an arable weed since 1863, but its spread has only increased significantly since the beginning of the 1990s.
A study conducted in Baden-Württemberg ten years ago estimated that 15 out of 100 Germans were already sensitised to ragweed (Behrendt 2010). At least two to five out of a hundred people also experience allergy symptoms – especially people who already have allergies. However, there are still no comprehensive data on the total number of people in Germany affected by ragweed allergy.

In the US, the plant’s country of origin, the numbers are high: The Allergy and Asthma Foundation of America estimates that 10 to 20 out of 100 Americans suffer from a ragweed allergy. Ragweed pollen is now the main trigger for allergic rhinitis in the US.

An abundance of small pollen grains

Ragweed is actually very allergenic: It takes relatively small amount of airborne pollen to cause an allergic reaction. As few as six pollen grains per cubic metre of air are considered to be allergenic. The amount for grass pollen is 50 pollen grains per cubic metre of air – more than eight times higher.


In addition, ragweed produces a lot of pollen: A single plant can release up to one billion pollen grains. And it has more time to do this than before. Compared to 1990, the allergy season in 2018 not only started 20 days earlier, but also lasted ten days longer. This point was recently raised by William Anderegg and his team of researchers at the University of Utah in Salt Lake City, USA.


Climate change is also likely to encourage the spread of ragweed. Higher temperatures allow ragweed to grow over a longer period of time. The plant needs a mild autumn to allow its seeds to mature and to reproduce.


What’s more, ragweed pollen is small and light. In Germany, ragweed plants and pollen grains are mainly found in the east and northwest, but the wind also carries the pollen to southern Germany.


As a consequence of all these factors, there are now more allergy sufferers with more symptoms, leading to more spending on the healthcare system. Each year, additional costs of  €200 million to more than €1 billion are incurred due to the spread of ragweed, as calculated by the Helmholtz Centre for Environmental Research (UFZ) and the Allergy Centre at the Ludwig Maximilian University of Munich in 2012.


What can be done about the allergy?

After testing for ragweed allergy, the treatment is the same as for other pollen allergies.

  • First of all, exposure to the pollen should be avoided as much as possible.
  • Allergic rhinitis and asthma are usually treated with antihistamines. Other therapy options include cortisone (as a nasal spray or inhaled), leukotriene receptor antagonists, short and long-acting beta-2 mimetics, theophylline, cortisone in tablet form and anti-IgE treatment.
  • Specific immunotherapy (hyposensitisation) can gradually allow the body to become accustomed to the allergen. This treatment is currently the only way to prevent allergic asthma. It should be used mainly in people with moderate to severe disease.


What can be done about the plant?

In order to reduce pollen levels, the plant must be kept from spreading. The Julius Kühn-Institut Federal Research Centre for Cultivated Plants launched the ‘Ambrosia Action Programme’ back in 2007. However, the measures – such as tearing out the plant and its roots or spraying it with hot water – are time-consuming and expensive. Although the German federal government, the federal states and local authorities have now recognised the problem and have in some cases initiated action and funding programmes, there are no uniform regulations yet.



Anderegg WR. Anthropogenic climate change is worsening North American pollen seasons. PNAS 2021; 118(7): e2013284118


Behrendt H et al. Health assessment of the spread of Ambrosia artemisiifolia in Baden-Württemberg: Risk or overestimation? Umweltmed Forsch Prax 2010;15(1):34–41


Born W et al. Gesundheitskosten der Beifuß-Ambrosie in Deutschland (Health costs due to mugwort ambrosia in Germany). Umweltmed Forsch Prax 2012;17(2): 201280 (In German)



Brenner B. Bavarian State Office for Health and Food Safety. Ambrosia artemisiifolia als Inhalationsallergen: Krankheitsbild, Häufigkeit, Auslöser, diagnostische Maßnahmen (Ambrosia artemisiifolia as an inhaled allergen: Disease pattern, frequency, trigger, diagnostic measures). Document dated 26 July 2019. Last retrieved on 28 September 2021 (In German)


Gabrio T et al. Sensitization to allergens of ambrosia artemisiifolia and other allergens on 10 years old children and adults in Baden-Württemberg. Umweltmed Forsch Prax 2010;15(1):15–22


Julius Kühn-Institut. Ambrosia artemisiifolia. Last accessed online on 28 September 2021 (In German)


German Environment Agency GE-I-3: Belastung mit Ambrosiapollen (Exposure to Ambrosiapollen. GE-I-3: Exposure to ragweed pollen). 2019 monitoring report on the German Strategy for Adaptation to Climate Change. Last accessed online on 28 September 2021 (In German)


Wissenschaftliche Dienste des Deutschen Bundestags. Gesundheitsrisiken durch den Kontakt mit der Ambrosiapflanze (Health risks due to contact with the ragweed plant). WD status report 9 – 3000 – 096/13. 2016. Last retrieved on 28 September 2021 (In German)

Tags: hay fever