Ragweed Allergy
Ragweed allergy is one of the hay fevers with the greatest clinical impact in specific areas of central and south-eastern Europe. In Italy, it is particularly widespread in the northern regions and, to a lesser extent, in some areas of central Italy. Ragweed pollen is among the most allergenic of all: it can cause sensitisation and symptoms even at very low concentrations in the environment. The pollen season, which runs from July to October, falls at a time when many other pollen allergies are already subsiding, significantly prolonging the discomfort experienced by patients with multiple sensitivities. Like other pollen allergies, it can be managed using an integrated approach that includes exposure reduction, drug therapy and, where indicated, allergen-specific immunotherapy (AIT).
[Chen KW, Marusciac L, Tamas PT, Valenta R, Panaitescu C. Ragweed Pollen Allergy: Burden, Characteristics, and Management of an Imported Allergen Source in Europe. Int Arch Allergy Immunol. 2018;176(3-4):163-80.
D'Amato G. et al. Ragweed allergy: epidemiology and clinical relevance in Europe. Allergy, 2015.]
What is ragweed and why is it so allergenic?
Ambrosia (genus Ambrosia, family Asteraceae) is an annual weed native to North America, now widely distributed across Europe. The species of greatest allergenic significance is Ambrosia artemisiifolia, which produces large quantities of highly sensitising pollen.
Unlike other allergenic plants, ragweed pollen can trigger reactions even at very low environmental concentrations — in the order of a few tens of grains per cubic metre of air — making it one of the most clinically aggressive pollen allergens.
Ragweed plants are opportunistic weeds that preferentially colonise ‘disturbed’ land: fallow fields, riverbanks, roadside verges, building sites and peri-urban areas. Their ability to adapt to different types of soil — whether fertile or poor — has facilitated their rapid spread across many regions of Italy, particularly in the Po Valley, where pollen concentrations are among the highest in Europe.
[Cecchi L. et al. Ambrosia artemisiifolia: impact on respiratory allergy in Europe. Eur Ann Allergy Clin Immunol, 2012]
Pollen season: when symptoms appear
Ambrosia allergy is a late-season hay fever: symptoms appear in summer and persist until late autumn, at a time when most spring hay fevers have already subsided.
- Start of flowering: July
- Pollen peak: late August – mid-September
- End of the season: late October
This timeline is particularly relevant for patients with multiple sensitivities, who may experience a virtually uninterrupted allergy season from March to October. Pollen concentrations are influenced by temperature, humidity and wind: hot, dry and windy days typically correspond to peaks in exposure.
[Gentili, R., et al., Ambrosia artemisiifolia L. temperature-responsive traits influencing the prevalence and severity of pollinosis: a study in controlled conditions. BMC Plant Biol, 2019. 19(1): p. 155.]
Immunological mechanism
In genetically predisposed individuals, the first exposure to ragweed pollen, which acts as an allergen, triggers the production of specific antibodies (IgE) by the immune system (a process known as sensitisation). Upon subsequent exposure, IgE bound to the surface of mast cells recognises the allergen and triggers the release of inflammatory chemical mediators — primarily histamine — which lead to the onset of symptoms.
The physical characteristics of ragweed pollen — its small size and surface rich in allergenic proteins — facilitate its deep penetration into the airways, potentially affecting the bronchi.
Chronic inflammation of the respiratory mucosa, if not properly treated, can, over time, contribute to increased sensitisation and progression to more severe forms of the disease, including bronchial asthma. [Bousquet ARIA JACI 2020]
Molecular allergens of ragweed
The ‘major’ allergen in Ambrosia artemisiifolia is Amb a 1, a protein present in high concentrations in pollen and responsible for the clinical symptoms in the majority of allergic individuals. It is considered the reference molecular marker for primary sensitisation to ragweed. However, other proteins are also important as they contribute to the severity of the clinical picture or are involved in cross-reactivity with other pollens and foods.
[Pichler, U., et al., Pectate lyase pollen allergens: sensitization profiles and cross-reactivity pattern. PLoS One, 2015. 10(5): p. e0120038.
Jahn-Schmid, B., et al., Humoral and cellular cross-reactivity between Amb a 1, the major ragweed pollen allergen, and its mugwort homolog Art v 6. J Immunol, 2012. 188(3): p. 1559-67.]
Symptoms of ragweed allergy
Symptoms appear during the pollen season and can be severe even at relatively low pollen concentrations, a characteristic that distinguishes ragweed from many other pollensevere allergens.
Nasal symptoms
- Repeated and intense sneezing
- Itchy nose
- Profuse watery nasal discharge
- Persistent nasal congestion
Eye symptoms
- Redness of the eyes
- Itchy and burning eyes
- Excessive tearing
Bronchial symptoms
- Dry cough
- Wheezing
- Dyspnoea (shortness of breath)
- Tightness in the chest
In some individuals, particularly during pollen peaks, bronchial symptoms may become particularly severe, even leading to acute asthma attacks. In patients with pre-existing bronchial asthma, the ragweed season represents a period of increased risk to disease stability.
Pollen and food cross-reactivity
Ambrosia pollen may exhibit cross-reactivity with other allergens, both pollen-based and food-based. This is due to the structural similarity between certain allergenic proteins in Ambrosia and those found in other pollens or plant-based foods.
Cross-reactivity with other pollens
Cross-reactivity with Artemisia (wormwood) pollen, a plant belonging to the same botanical family (Asteraceae), has been documented. Patients sensitised to ragweed may therefore experience mild symptoms in response to exposure to mugwort pollen. The presence of ‘pan-allergens’ (e.g. profillins, polcalcins) in ragweed pollen also explains cross-reactivity with the pollen of other species.
[Asero, R., et al., Concomitant sensitization to ragweed and mugwort pollen: who is who in clinical allergy? Ann Allergy Asthma Immunol, 2014. 113(3): p. 307-13.]
Cross-reactivity with foods
Cross-reactions have been reported with certain plant-based foods, including banana, watermelon, melon, pumpkin, cucumber, celery, chamomile and sunflower seeds. Symptoms typically present as oral allergy syndrome (localised itching and swelling in the mouth) and are generally mild and self-limiting.
[Asero R, Mistrello G, Amato S. The nature of melon allergy in ragweed-allergic subjects: A study of 1000 patients. Allergy Asthma Proc. 2011;32(1):64-67.]
Popescu FD. Cross-reactivity between aeroallergens and food allergens. World J Methodol. 2015;5(2):31-50.
The presence of cross-reactivity does not necessarily imply the onset of clinical symptoms in all sensitised individuals: clinical significance must be assessed on a case-by-case basis by an allergy specialist, including through the use of molecular diagnostic techniques.
Impact on quality of life
Ambrosia allergy is recognised as one of the hay fevers with the greatest impact on the quality of life of those affected, due to a combination of three factors: the high allergenicity of the pollen, the length of the pollen season and the frequent severity of symptoms.
The most significant consequences for the patient include:
- Sleep disturbances due to nocturnal nasal and bronchial symptoms
- Reduced ability to concentrate and impaired performance at work or school
- Restriction of outdoor activities during the summer and autumn
- Worsening of asthma in patients with bronchial comorbidities
- A prolonged allergy season in patients with multiple sensitivities
In patients with asthma, the global guidelines GINA and ARIA, for the management of allergic rhinitis and asthma, emphasise the importance of identifying and managing pollen triggers as part of an integrated treatment plan, particularly during periods of high pollen counts.
[Laurent Laforest, Jean Bousquet, Guilhem Pietri, Vasilisa Sazonov Kocevar, Donald Yin, Yves Pacheco, Eric Van Ganse. Quality of life during pollen season in patients with seasonal allergic rhinitis with or without asthma. Int Arch Allergy Immunol. 2005 Mar;136(3):281-6] Bousquet J, et al; Aria Workshop Group; World Health organization. Allergic rhinitis and its effect on asthma. J Allergy Clin Immunol 2001; 108: S147–S334.
Global Initiative for Asthma. Global Strategy for Asthma Management and Prevention, 2025. Updated 15 November 2025. Available from: www.ginasthma.org.
Reducing exposure: practical measures
Unlike indoor allergens, reducing exposure to ragweed pollen is more difficult to achieve. However, certain measures can help to limit exposure during times and in situations where pollen concentrations are highest.
- Monitor regional pollen forecasts and limit time spent outdoors on days when pollen concentrations in the air are high
- Avoid outdoor activities during the middle of the day, when pollen concentrations are highest
- Keep windows closed during pollen peaks and use air conditioning fitted with suitable filters
- Take a shower and change your clothes after being outdoors
- Wear wraparound sunglasses to reduce contact with the eye’s mucous membranes
- Avoid areas with a high presence of ragweed (uncultivated fields, riverbanks, roadsides)
These exposure-reduction measures are provided for information purposes and should be regarded as complementary to drug therapy and any immunotherapy, as part of a treatment plan agreed with your doctor.
Frequently asked questions
The distribution of ragweed in Italy is uneven. The highest concentrations are found in the northern regions, particularly in the Po Valley (Lombardy, Piedmont, Veneto, Emilia-Romagna), where pollen levels can reach some of the highest in Europe. In the central and southern regions, its presence is currently more limited, but the plant is gradually spreading.
An allergy to ragweed differs from spring pollen allergies (caused by grasses and trees) in terms of the season in which symptoms appear, which begins in July and lasts until October. The simultaneous presence of severe nasal, ocular and bronchial symptoms in the height of summer or autumn, in the absence of a common cold, is a sign that points towards the need for a specific allergy assessment.
Yes. Without appropriate treatment, allergic rhinitis caused by ragweed can progress to involve the lower airways (bronchial asthma), in a process known as the ‘allergic march’. In patients who already have asthma, seasonal exposure to ragweed pollen can contribute to the destabilisation of the condition. For this reason, early diagnosis and active management are essential.
Yes. In addition to symptomatic drug therapy (antihistamines, nasal and inhaled corticosteroids, and bronchodilators in patients with asthma), allergen-specific immunotherapy (ASI) using ragweed extracts is a treatment capable of modifying the patient’s immune response, reducing sensitisation and the long-term progression of the disease. Suitability for immunotherapy must be assessed by an allergy specialist.
On days when pollen concentrations are high, it is advisable to limit outdoor activities, particularly during the hottest and windiest parts of the day, to keep windows closed, and to take the medication prescribed by your doctor as directed. Asthma patients should ensure they always carry their emergency medication with them and follow the instructions in the action plan agreed with their doctor.
You should see your doctor if you experience persistent respiratory or eye symptoms that occur regularly in summer or autumn, that limit your daily activities, or that do not respond adequately to over-the-counter medicines. An allergy assessment involving specific tests can confirm the diagnosis and help tailor the most appropriate treatment to the patient’s individual circumstances.
Practical information
Information note
The information contained on this page is for informational purposes only and is not a substitute for the advice of a doctor or other qualified healthcare professionals. For a clinical assessment and any treatment decisions, including the selection and management of drug therapies and allergen-specific immunotherapy, you should consult your specialist doctor. The practical guidelines provided are intended as complementary measures to support exposure management, as part of an individualised treatment plan.