Allergy to olive pollen
Olive pollen allergy is one of the main causes of hay fever in Mediterranean regions, being particularly prevalent in southern Italy, the islands and Liguria. The pollination season is relatively short – around 4–6 weeks between late April and late June – but can produce pollen peaks of exceptional intensity, with atmospheric concentrations among the highest of all allergenic pollens. The olive tree tends to induce polysensitisation, often in association with grasses, pellitory and other Oleaceae such as ash and privet. A unique biological characteristic of the olive tree is the marked interannual variability in pollen production, which results in allergy seasons of very different intensity from one year to the next.
Azofra J. Olive allergy. Allergy. 2004;59(5):559.
What is the olive tree and why is it relevant in allergy terms?
The olive tree (Olea europaea, family Oleaceae) is one of the most characteristic and widespread trees in the Mediterranean landscape. In Italy, it is widely cultivated throughout the central and southern regions, on the islands and in certain northern areas with favourable climatic conditions – in particular Liguria and the shores of the pre-Alpine lakes. With around 1.2 million hectares under cultivation, Italy is one of the world’s leading producers of olives and olive oil.
The allergological significance of the olive tree stems from two converging factors: the plant’s widespread geographical distribution across the areas where the majority of the Italian population lives, and the high allergenicity of its pollen, which can reach exceptionally high atmospheric concentrations during flowering. In some cities in southern Italy and on the Iberian Peninsula, olive pollen concentrations during the peak flowering period are among the highest recorded for any allergenic species.
In addition to cultivated plants, the wild olive tree (olivastro) contributes to pollen production in many areas of the Mediterranean, further increasing the spread of pollen in the environment.
Orlandi F, Garcia-Mozo H, Galán C, Romano B, de la Guardia CD, Ruiz L, del Mar Trigo M, Dominguez-Vilches E, Fornaciari M. Olive flowering trends in a large Mediterranean area (Italy and Spain). Int J Biometeorol. 2010 Mar;54(2):151-63.
Feo Brito, F., Mur Gimeno, P., Carnés, J., et al. Olea europaea pollen counts and aeroallergen levels predict clinical symptoms in patients allergic to olive pollen. Annals of Allergy, Asthma & Immunology 106(2):146–152 (2011).
Pollen season: short, intense and variable
The most characteristic feature of the olive tree’s pollen season is the combination of short duration and extremely high intensity of the peaks – a profile that differs, for example, from that of pellitory, which is instead characterised by a long duration, often with multiple peaks but with more moderate concentrations.
- Flowering period: late April to late June, with variability linked to seasonal trends and geographical area
- Average duration: 4–6 weeks per site, but variability between cultivars and microclimates can prolong the overall exposure
- Pollen peak: concentrated over a few days, often within a period of 1–2 weeks, with concentrations that can reach thousands of grains per cubic metre of air
- Time of greatest dispersal: the morning hours on hot, dry days
Pollen concentration is strongly influenced by weather conditions: high temperatures, wind and low humidity favour pollen dispersal and the attainment of peak levels; rainfall rapidly reduces concentrations. In areas with a high density of cultivation, the pollen peak can make it difficult for individuals who are not adequately treated to carry out any outdoor activities.
Liccardi, G., D'Amato, M., & D'Amato, G. (1996). Oleaceae pollinosis: a review. International Archives of Allergy and Immunology, 111, 210–217.
Galán C, García-Mozo H, Cariñanos P, Alcázar P, Domínguez-Vilches E. The role of temperature in the onset of the Olea europaea L. pollen season in southwestern Spain. Int J Biometeorol. 2001 Feb;45(1):8-12.
Interannual variability: alternate bearing in the olive tree
A biological characteristic of the olive tree, with direct clinical implications for allergy sufferers, is the phenomenon of ‘alternate bearing’: the olive tree tends to produce in an alternating pattern, with years of abundant flowering and fruiting followed by years of reduced production.
This biological mechanism results in marked interannual variability in atmospheric pollen concentrations. A patient experiencing a season with severe symptoms might see a significant improvement the following year, only to find themselves with intense symptoms again in the third year. This variability can make it difficult to subjectively assess the course of the disease and highlights the importance of not altering the treatment plan based solely on the perceived severity of symptoms.
Rojas-Gómez, M., et al. (2023). Pollen production in olive cultivars and its interannual variability. Annals of Botany, 132, 1145–1158.
Molecular allergens of the olive tree
The main allergen in olive pollen is Ole e 1, considered the most significant molecular marker of sensitisation for this pollen allergy. Ole e 1 is recognised by the vast majority of patients sensitised to olive (over 80–90 per cent of cases) and plays a central role in the activation of the IgE-mediated response. Its identification via molecular diagnostics confirms primary sensitisation to olive.
Esteve C, Montealegre C, Marina ML, García MC. Analysis of olive allergens. Talanta. 2012;92:1-14.
Villalba M, Rodriguez R, Batanero E. The spectrum of olive pollen allergens. From structures to diagnosis and treatment. Methods. 2014;66(1):44-54.
Scala E, Abeni D, Pomponi D et al. Ole e 1, Ole e 7, and Ole e 9: Identifying distinct clinical subsets of olive tree allergic patients. J Allergy Clin Immunol 2015; 137(2):629
Sensitisation and polysensitisation profile
Olive tree allergy is frequently associated with a profile of polysensitisation: the majority of patients allergic to olive trees are also sensitised to other pollens.
The most common cross-sensitisation involves:
- Grasses: olive-grass co-sensitisation is common in Mediterranean regions, where the two pollen seasons partially overlap; this overlap can exacerbate spring-summer symptoms
- Cypress: in areas where both plants are widespread, cross-sensitisation can result in pollen exposure spanning from late winter through to summer
- Parietaria: cross-sensitisation is very common in the Mediterranean region
- Other Oleaceae, however, such as ash (Fraxinus excelsior) and privet (Ligustrum vulgare), contain allergens that are highly cross-reactive with those of the olive tree.
Symptoms of olive pollen allergy
Symptoms typically affect the upper and lower respiratory tracts and the mucous membranes of the eyes. In untreated individuals, peaks in pollen concentration can cause severe symptoms, concentrated over a few days but with a significant impact on well-being and the ability to work.
The severity of symptoms is closely linked to daily atmospheric pollen concentrations. In patients who are hypersensitive to both olive tree and grasses, the period when the two seasons overlap can lead to a particularly significant worsening of symptoms.
Nasal symptoms
- Repeated sneezing, often in fits
- Intense nasal itching
- Profuse watery nasal discharge
- Nasal congestion
Eye symptoms
- Redness and severe itchy eyes
- Excessive tearing
- Photophobia in severe cases
Bronchial symptoms
- Dry cough
- Wheezing
- Dyspnoea (shortness of breath)
- Chest tightness
Olive trees and asthma
In patients with bronchial asthma, exposure to olive pollen during the seasonal peak is one of the most significant risk factors for the stability of disease control. The exceptional intensity of pollen peaks can lead to the rapid onset or worsening of bronchial symptoms, even in patients whose condition is well controlled during other seasons.
The international scientific consensus documents ARIA and GINA, on the management of allergic rhinitis and asthma, highlight the link between allergic rhinitis and bronchial asthma within the model: ‘one airway, one disease’. Appropriate treatment of olive-induced allergic rhinitis is an integral part of asthma management.
For asthmatic patients allergic to olive trees, it is particularly important to monitor regional pollen forecasts throughout the season, to always have emergency asthma medication to hand, and not to stop or alter their maintenance treatment without medical advice.
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.
Pollen cross-reactivity
The olive tree belongs to the Oleaceae family and shares allergenic structures with other species of the same family found in Europe and the Mediterranean region.
Cross-reactivity with other Oleaceae
Cross-reactivity between the olive tree, ash tree and privet is clinically significant and well documented. The major allergen in ash (Fra e 1) and that in privet (Lig v 1) show a high degree of homology with Ole e 1. In patients sensitised to Ole e 1, cross-reactivity with ash and privet is therefore common and clinically significant.
In Italy, ash trees typically flower earlier than olive trees (February–April in the northern regions), which can result in allergenic pollen exposure extending from late winter to early summer for patients sensitised to this family.
Niederberger V, Purohit A, Oster JP et al. The allergen profile of ash (Fraxinus excelsior) pollen: cross- reactivity with allergens from various plant species. Clin Exp Allergy 2002; 32(6):933-41.
Cross-reactivity with grasses
Possible cross-reactivity between olive and grasses, mediated by shared allergens, has been documented. This cross-reactivity is clinically less significant than that with other Oleaceae, but may contribute to the polysensitisation profile observed in Mediterranean patients. The diagnostic distinction between the two sensitivities requires molecular assessment.
Cross-reactivity with foods
Unlike what is observed with birch (birch-fruit-vegetable syndrome), with grasses and with pellitory, clinically relevant cross-reactivity between olive trees and foods is not commonly reported. With rare exceptions, the consumption of olive oil and olives does not cause allergic reactions in individuals sensitised to pollen, as the ripening and processing stages degrade the allergenic proteins.
Unsel M, Ardeniz O, Mete N, Ersoy R, Sin AZ, Gulbahar O, et al. Food allergy due to olive. J Investig Allergol Clin Immunol. 2009;19(6):497-9.
Impact on quality of life
The short duration of the season does not necessarily reduce the impact on quality of life: the combination of high pollen concentrations and severe symptoms concentrated over a few weeks can result in a significant clinical ‘burden’—that is, a significant impact—with consequences for daily well-being, work and academic performance, sleep quality and the ability to engage in outdoor activities.
- Intense acute symptoms during the pollen peak, even in individuals with mild to moderate rhinitis during other seasons
- Sleep disturbances due to night-time and morning symptoms
- Reduced work and academic performance during peak weeks
- Restrictions on outdoor activities, which are particularly significant in rural areas with intensive farming
- Risk of asthma exacerbations in people with pre-existing asthma
- Year-to-year variability, which can make it difficult to manage treatment expectations
Reducing exposure: practical measures
During the olive tree’s seasonal peak, reducing exposure to pollen can help to limit the severity of symptoms in conjunction with drug therapy. The measures listed below are complementary to treatment and do not replace it.
- Check regional pollen forecasts daily and plan outdoor activities for days with low pollen concentrations or during the evening and night-time hours
- Keep windows closed during the middle of the day at the peak of the season; ventilate preferably in the evening or after rainfall
- Use air conditioning with pollen filters indoors and in the car
- Take a shower and change your clothes when returning indoors on days when pollen levels are at their peak
- Wear wraparound sunglasses to reduce contact between pollen and the conjunctival mucous membranes
- Avoid areas with high concentrations of crops on hot, dry and windy days that coincide with the peak flowering season
- Do not stop your medication even on days when symptoms are temporarily reduced
These exposure-reduction measures are provided for information purposes and should be regarded as complementary to medication and any immunotherapy, as part of a treatment plan agreed with your doctor.
Frequently asked questions
The olive tree produces and releases exceptionally high quantities of pollen over a very short period of time. During the peak flowering period, atmospheric concentrations can reach some of the highest levels ever recorded for any pollen species. This combination of high allergenicity and massive concentration triggers a very intense immune response in sensitised individuals, with symptoms that are often more severe than those of other pollinoses characterised by longer seasons but lower concentrations.
Yes, this is a well-documented phenomenon in olive tree allergy. The olive tree’s alternate bearing cycle — a biological characteristic of the plant that leads to years of abundant flowering alternating with years of reduced production — results in marked year-to-year variability in atmospheric pollen concentrations. A year with severe symptoms may be followed by one with much milder symptoms, regardless of how your allergic sensitisation has developed. This should not lead you to change your treatment plan without medical advice.
Generally, yes. Sensitisation to olive pollen does not typically result in reactions to the ingestion of olive oil or olives. The processes of fruit ripening and oil production break down the allergenic proteins in the pollen, making them unrecognisable to the immune system. Cases of reactions to the consumption of olive oil or olives in patients allergic to olive pollen are rare and should be reported to an allergy specialist for an individual assessment.
Cross-reactivity between olive, ash and privet is common and clinically significant, due to the high similarity between their respective major allergens. Many patients allergic to olive may also experience symptoms in the presence of ash or privet pollen. The clinical significance of cross-reactivity must be assessed by an allergy specialist, who will be able to recommend any specific precautionary measures tailored to the individual’s sensitisation profile.
Allergen-specific immunotherapy (AIT) using olive pollen extracts is available and is a treatment option that can be effective in helping to reduce symptoms and the use of symptomatic medication. The indication for and suitability for AIT must be assessed by an allergist.
Yes. Climate data show that the start of the olive flowering season is occurring earlier in many Mediterranean areas, in line with rising average winter and spring temperatures. In some regions, more intense pollen seasons are also being observed as a result of increased atmospheric CO₂ levels. These changes have direct clinical relevance for allergy sufferers and highlight the importance of up-to-date pollen monitoring.
You should see a doctor if you experience nasal, eye or bronchial symptoms that occur regularly in spring, coinciding with the olive blossom season, and which do not respond adequately to over-the-counter medicines. An allergy assessment involving skin prick tests and, where indicated, molecular diagnostics, allows the diagnosis to be confirmed, the sensitisation profile to be determined and the most appropriate treatment plan to be established before the start of the following season.
Practical insights
Information notice
The information 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 choice 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.