While many of us are rejoicing the arrival of spring, some of us may not be too excited. And for good reason. Hay fever season is once again upon us! Pollen allergy is more than sneezing and wheezing. It is a chronic disease that should be taken seriously and treated. With us currently fast approaching the prime pollen allergy season, it’s time to give you a rundown of hay fever symptoms, causes and treatment.
Watery eyes, constant sneezing, coughing or shortness of breath – pollen allergy symptoms are annoying and often limit the quality of life of those affected.[1, 2] Unfortunately, hay fever season is no longer limited to spring and summer months. The reason is climate change: the plants’ leaves and buds bloom earlier, and pollen remains in the air for longer – causing problems well into the autumn.
What many people don’t know is that pollen allergy is a chronic respiratory disease that should be treated. If this does not happen, the allergy can worsen from year to year and even lead to asthma – both pollen allergy and asthma will then persist for a lifetime. For those who seek treatment at an early stage, it is possible to test whether special immunotherapy, known as hyposensitisation, may be suitable. This can reduce the symptoms of pollen allergy and the risk of asthma.
But what exactly does a pollen allergy do to the body? How can it be diagnosed? Can a pollen allergy be prevented? Are there forms of pollen allergy treatment available? Find out in our article. You will also learn what influence the weather – for example, rain and thunderstorms – has on pollen and what you can do to relieve hay fever symptoms.
What is hay fever and its symptoms?
With a pollen allergy, often also referred to as hay fever, the body has an allergic reaction to the pollen of certain plants. Many plant species use pollen to spread their male genome. Heavy pollen grains can be transported by insects such as bees, whereas light pollen grains spread with the wind and thus ensure the survival of the plant species.
This wind-pollinated pollen are only 10 to 20 micrometres in size and can easily be inhaled by humans. For pollen allergy sufferers, normally harmless pollen triggers a violent allergic reaction in the body – especially in parts of the body that come into contact with the pollen: nose, eyes, skin and respiratory tract. Those affected suffer from swollen and irritated eyes, a cold or a dry cough. These and other symptoms of hay fever are also known as allergic rhinitis.
Did you know that the term ‘hay fever’ originates from the observation that contact with hay causes symptoms in people with a grass pollen allergy – due to the pollen also present in hay. The word ‘hay fever’ is also often used for allergies to pollen from plants, such as birch, alder or hazel.
In the United Kingdom, approximately 10 to 30 per cent of adults suffer from a pollen allergy. Children and adolescents can also be affected – 40 per cent of them have been diagnosed with a pollen allergy.
What triggers hay fever?
When inhaled, small protein components in plant pollen reach the mucous membranes of your nose and lungs. The proteins are actually harmless, but for pollen allergy sufferers, they are classified as dangerous by the body. The immune system then develops special IgE antibodies tailored to fight the pollen proteins. The IgE antibodies bind to mast cells. The antibodies on these mast cells are able to immediately recognise the allergen (that is, the pollen proteins) when it next enters the body. This process is called sensitisation.
The antibodies on the mast cells recognise the pollen proteins and bind them. The mast cells then release messenger substances. The messenger substance histamine triggers typical hay fever symptoms: sneezing, red, watery eyes, and coughing.[11, 14]
Tip: You can learn more about the messenger substance histamine in our health article about histamine intolerance.
The pollen allergy is considered a type 1 allergy: the immediate type. This means that pollen allergy symptoms occur immediately after contact with the allergen. Symptoms can still occur up to six hours later.
Did you know that genes also play a role in pollen allergy? The more family members are affected, the higher the risk for children in this family to develop an allergic disease as well. For example, if both parents have the same allergy, 50 to 70 per cent of the children will also develop one.
What are typical pollen allergy symptoms?
Typical pollen allergy symptoms include the following:
- runny or stuffy nose
- frequent sneezing, itchy nose
- watery, itchy, inflamed eyes
- skin reactions – especially in the face (welts, itching, swelling, eczema)
- exhaustion and fatigue
- headache, migraine
Some of those affected report light-sensitive eyes and a deteriorated sense of smell and taste. A pollen allergy may also lead to asthma. People with hay fever should pay attention to the following hay fever symptoms – they can be an indication that they are developing asthma:
- Dry irritable cough (during physical exertion or outdoors)
- Burning sensation behind the sternum (when breathing in)
- For children: decrease in athletic performance, physical condition
- Frequent infections of the lower airways (bronchitis)
What foods cross react with pollen?
Anyone suffering from a pollen allergy and those who also cannot tolerate certain foods may have developed a cross sensitivity. This is due to the similar biochemical composition of pollen: the protein building blocks of birch pollen are so similar to those of apple pollen – for example, that the immune system in some cases regards both as identical and fights them equally. This cross-sensitivity is therefore also called pollen-associated food allergy.
In affected people, eating an apple can now trigger the so-called oral allergy syndrome (OAS). Swelling, itching and tingling on the tongue and in the mouth and throat can occur. Swelling of the lips, tongue or throat can even be life-threatening.
Tip: Read more in our Health Portal about the differences between a food allergy and intolerance.
Studies show that 20 to 70 per cent of those allergic to pollen develop symptoms of OAS after eating fresh fruit, raw vegetables, nuts or certain herbs. People with birch pollen allergy are particularly often allergic to plant-based foods: in Central and Northern Europe, 80 per cent of birch pollen allergy sufferers are allergic to stone and pome fruits, nuts and vegetables.
An overview of the most important cross-allergens can be found here:
The classic cross-allergens to birch pollen are:
- Stone and pome fruit (e.g. apple, pear, cherry, plum, nectarine)
- Nuts (e.g. hazelnut, Brazil nut, walnut)
- Vegetables (e.g. celery, carrot)
- Various spices
The classic cross-allergens to mugwort pollen are:
- Herbs and spices (aniseed, garlic, fennel, pepper, etc.)
The classic cross-allergens to grass and wheat pollen are:
- Soya and soya products
- Wheat flours
- Peanuts and peanut products
Most allergens in fruit and vegetables can be destroyed by heating – this means that the food is tolerated by allergy sufferers when steamed, grilled or cooked. Caution: Celery, herbs and spices can still cause discomfort even after cooking!
How does the weather affect pollen allergy symptoms?
Hay fever occurs mainly in spring and summer, the time when most plants are in bloom. However, each plant species has a different blooming period, which depends on the geographical location and weather conditions. Trees such as hazel and alder, for example, bloom depending on temperature. As soon as the daytime temperature in the winter months rises above five degrees Celsius, blooming begins – and with it, pollen is produced.
In addition, most pollen allergy sufferers react to the pollen of multiple plants. Those affected consequently have to struggle with hay fever symptoms for several months. According to experts, hay fever season currently lasts from January to October.
Pollen allergy: when is hay fever season?
The following is a summary of information about the plants whose pollen is particularly likely to trigger an allergy during the blooming period. The pollen comes from trees, grasses and herbs.[11, 19]
Table: United Kingdom’s most important allergenic plants with blooming periods
|Trees||Where is it found?||Bloom/Pollen season|
|Hazel||In deciduous woods, along forest edges, gardens||January–April. As soon as it’s warmer than five degrees during the day.|
|Alder||Along streams and banks of lakes and rivers||January–April. As soon as it’s warmer than five degrees during the day.|
|Birch||Forest edges, field shrubs, heaths, moors, fallow land||March–June|
|Grasses and grains|
|Sweet grass, e.g. rye||Widespread||May–August|
|Mugwort||Rubble, alluvial bushes, meadows, along roadsides and shores||June–September|
|Ragweed||On fallow land, rubble heaps, along roadsides and gardens||August–September|
How is pollen allergy affected by rain?
To distribute their genetic material, pollenating plants release their pollen into the air. Light pollen can fly hundreds of kilometres. The windier it is, the more pollen is spread and the further it goes, too. When it rains, however, allergy sufferers usually feel a sense of relief: pollen falls to the ground, meaning the air is free of pollen and causes fewer complaints for those affected.
What is thunderstorm asthma?
If a thunderstorm occurs during the pollen season, people with pollen allergy should be careful: during a thunderstorm, pollen allergy symptoms can increase significantly in the initial 20 to 30 minutes.
Before a storm, winds often occur. Based on studies, it is assumed that these winds collect large quantities of flower pollen from upper layers of air. Through strong downward winds, the air masses with the pollen reach the bottom and reach the air we breathe.
During thunderstorm rain, pollen is crushed by the rain, releasing many particles. Pollen particles are then so small that they can penetrate deep into the lower respiratory tract, the bronchi. In people who are allergic to pollen, such conditions can intensify asthma symptoms or even trigger them for the first time.
Recommendation: People with hay fever should stay indoors and keep windows and doors closed before and during a thunderstorm.[22, 23]
Pollen allergy diagnosis: how do you know if you are allergic to pollen?Do you suspect that you might suffer from a pollen allergy? Here is how you can diagnose hay fever! Common methods used to diagnose allergies are skin and blood tests.
The prick test is the standard test for suspected allergies of the immediate type (type I), which also includes pollen allergy or hay fever. The prick test is performed on the skin.
How the prick test works
Small drops of allergen solutions are applied to the skin – usually on the forearm or back. A needle is then used to prick the skin through the drop. A positive allergic reaction on the skin is evident within a few minutes by reddening and a welt (itchy, roundish skin elevation) around the test site.
The size of these welts determines the extent of the reaction and the diameter is recorded on the test sheet. Welts with a diameter of three millimetres or more indicate an increased allergy readiness – that is, sensitisation.
Please note: Doctors only diagnose you with an allergy if you’re also experiencing pollen allergy symptoms!
How does the IgE test work?Sensitivity to pollen can also be detected by measuring IgE antibodies in the blood. Should your body have an allergic reaction to certain pollen, it releases IgE antibodies to switch off the allergens. The antibodies can be detected in blood serum and provide information about whether and which pollen allergy is present. Just as with the prick test, experts can diagnose an allergy if the test is positive and allergy symptoms occur at the same time.
You can take a pollen allergy test at home. This means that you use the kit to take a small blood sample at home and send it to a specialist medical laboratory. The laboratory will analyse the concentration of IgE antibodies against different pollen.
The blood test offers an impressive advantage in that it can be used when a prick test is not possible. For example, if the skin is acutely irritated or you are taking medication that would suppress the body’s immune response.
How do doctors test for hay fever?
- Do siblings or parents have allergies?
- In which months do symptoms appear?
- How and when do symptoms appear?
Pollen allergy treatment: what can I do?Pollen allergy treatment essentially depends on the hay fever symptoms and on how well the pollen allergen causing it can be avoided. Actually, avoiding pollen is the most important step you can take to prevent symptoms – but in reality, this is difficult to implement because pollen is inevitably in the air we breathe. Other options include hyposensitisation and taking medication. Here are six practical tips you can use every day to relieve those pesky hay fever symptoms.
Are you planning your next holiday? Allergologists recommend that people with hay fever spend several weeks by the sea or in the mountains. The air there contains very little pollen and offers hay fever relief to those affected, especially during peak hay fever season.
What is hyposensitisation?During hyposensitisation, also known as allergen immunotherapy, the body is first given a very low, then slowly increasing dose of pollen allergens, usually at intervals of several weeks. In this way, the body is gradually accustomed to the pollen over a longer period of time, so that the immune system does not react to it. Hyposensitisation should begin three to four months before the start of the pollen season – otherwise, too many allergens could act on the body at the same time.
During hay fever season, treatment can then be continued to a lesser extent or interrupted completely. Hyposensitisation lasts about three years. Studies suggest that hay fever hyposensitisation may prevent the development of asthma in children. However, children undergoing this form of treatment should be at least five to six years old.
What about pollen allergy treatment with medication?If hay fever symptoms are very severe during the pollen season or if, for example, mucous membranes become inflamed, medication is recommended. Benefits are two-fold: hay fever symptoms improve and the risk of asthma can be reduced.
Cromones: Cromones are the mildest medication and are often prescribed to pregnant women. Cromones inhibit the release of histamine and thus prevent allergic inflammatory reactions. It is recommended to use them as a precautionary measure one week before pollen season begins. Cromones are available as nasal spray or eye drops.
Please note: Medications can relieve symptoms, but they do not eliminate the causes of the pollen allergy.
Cortisone: Cortisone has an anti-inflammatory effect, permanently relieves runny noses and reduces your nasal mucous membranes from swelling. However, cortisone also has side effects: nosebleeds, a dry nose and irritation in the throat may occur. Cortisone is available as a nasal spray. For severe allergic symptoms, pills or injections are also possible.
According to current research, several factors contribute to the development of allergies; these include hereditary predispositions and various environmental factors which – if a predisposition exists – influence the development and severity of an allergy. Experts suspect that allergies develop in early childhood. Many expectant parents therefore often wonder whether they can prevent their child from developing a pollen allergy.
Can you prevent a pollen allergy?
The good news is that there are several measures you can take during pregnancy, but also after the birth of your child, to reduce the risk of developing a pollen allergy.
Are there recommendations during pregnancy?
- Eat a healthy and balanced diet. Do not follow certain restrictive diets – that is, do not avoid food allergens (milk protein, nuts, cereals, etc.) – unless there are health-related reasons for this, such as gluten intolerance.
- Eat fatty fish such as salmon, herring or mackerel regularly. There are indications that the omega-3 fatty acids these contain can reduce the risk of allergy in a newborn.
Are there recommendations after birth?
- Breastfeed your newborn, if possible, at least for the first four months.
- If one of the parents suffers from an allergy and you cannot breastfeed, you should give your newborn baby special hydrolysed formula. The milk powder consists of ingredients with low allergenicity.
- Eat fatty fish regularly – even when breastfeeding.
- After the end of your infant’s first month, a supplementary diet should be introduced. Fish could reduce the risk of allergies. For this reason, give your child fatty fish regularly during the first year of its life.
- Make sure your child does not become overweight or obese.
General lifestyle recommendations
- If you already have an allergy in your family and your child is therefore exposed to an increased risk of allergies, you should not get cats. According to current studies, keeping dogs is not associated with a higher risk of developing allergies.
- Do not use any special allergy products, such as mite mattress protectors or similar products if you do not suffer from such an allergy.
- Avoid indoor climates that promote mould. You should air out your home on a regular basis!
- Avoid fast food as much as possible.
- Cigarette smoke increases the risk of allergies! Avoid active and passive smoking during pregnancy and especially in the presence of your child.
- Your child should be exposed as little as possible to air pollutants, such as car exhaust or volatile gases (produced, for example, during painting work).
Pollen allergy symptoms & hay fever season – at a glance
What is pollen allergy and how is it triggered?With a pollen allergy (hay fever), the body reacts to plant pollen. The immune system forms antibodies (IgE antibodies) against pollen components (allergens) and thus tries to fend off the supposedly harmful substances. This leads to what is called sensitisation. If the body comes into contact with the allergen again, the immune system releases messenger substances that trigger allergic reactions.
Those affected often suffer from an itchy, runny or stuffy nose with frequent sneezing. Your eyes may water, itch or become inflamed. People who are allergic to pollen can also have skin reactions – often hives, itching, swelling or eczema on the face. Hay fever can be accompanied by fatigue, headaches or migraines. Some sufferers report light-sensitive eyes and a deteriorated sense of smell and taste. A pollen allergy can even lead to asthma.
What are typical pollen allergy symptoms?
Each allergenic plant has a certain blooming period – during this period, symptoms occur. Plants bloom depending on the season, some also depending on the temperature. The blooming period is also influenced by geographical location. According to experts, the pollen season in central Europe currently runs from January to October.
When is hay fever season?
When it rains, the pollen in the air sinks to the ground, so that pollen is removed from the air and causes less discomfort for people with pollen allergies. Be careful during thunderstorms, as hay fever symptoms can worsen significantly and even cause asthma! People with hay fever should stay indoors and keep windows and doors closed before and during a thunderstorm.
How does the weather influence hay fever symptoms?
Skin or blood tests are available for the diagnosis of a pollen allergy. The skin test, or the prick test, involves applying drops of allergen solutions to the skin and introducing them into the bloodstream through a needle. Redness and welts – that is, markers of sensitisation or an allergic reaction – are documented. The blood test means that sensitisation to pollen can also be detected by measuring the IgE antibodies in the blood. Should your body react allergic to certain pollen, it releases IgE antibodies to switch off the allergens. The antibodies can be detected in blood serum and provide information about whether and which pollen allergy is present.
How can I find out if I am suffering from a pollen allergy?
The treatment of hay fever depends on the severity of the symptoms and how well the pollen allergen that causes them can be avoided. Avoiding pollen is the most important step you can take to avoid symptoms. Other options include hyposensitisation and taking medication.
What are the forms of pollen allergy treatment?
According to the current state of research, allergies usually develop in early childhood. There are various measures you can take during pregnancy, but also after the birth of your child, to ensure that the risk of developing a pollen allergy is reduced. For example, it is recommended to eat a balanced diet rich in omega 3 during pregnancy and breastfeeding.
Can a pollen allergy be avoided?
 Bousquet, J. et al. ‘Work productivity in rhinitis using cell phones: The MASK pilot study’, Allergy, vol. 72(10), 1475–1484, 2017, doi: 10.1111/all.13177.
 Bousquet, J. et al. ‘The Allergic Rhinitis and its Impact on Asthma (ARIA) score of allergic rhinitis using mobile technology correlates with quality of life: The MASK study’, Allergy, vol. 73(2), 505–510, Feb. 2018, doi: 10.1111/all.13307.
 ‘Klimawandel und Pollenallergien’, Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit, available at https://www.bmu.de/themen/gesundheit-chemikalien/gesundheit-und-umwelt/klimawandel-und-gesundheit/allergien/klimawandel-und-pollenallergien/, accessed on 23 June 2020.
 ‘WHO | Allergic rhinitis and sinusitis’, World Health Organization, available at https://www.who.int/respiratory/other/Rhinitis_sinusitis/en/, accessed on 10 June 2020.
 ‘Schlimmer, als viele wissen: Heuschnupfen’, AEDA - Ärzteverband Deutscher Allergologen e.V., available at https://www.aeda.de/presse/pressearchiv/einzelansicht/?tx_ttnews%5Btt_news%5D=234&cHash=0e0d9cc4ddcffa1bf00cccf13c92ef9d, accessed on 10 June 2020.
 Möller, C. et al. ‘Pollen immunotherapy reduces the development of asthma in children with seasonal rhinoconjunctivitis (the PAT-study)’, Journal of Allergy and Clinical Immunology, vol. 109(2), 251–256, Feb. 2002, doi: 10.1067/mai.2002.121317.
 ‘Heuschnupfen » Was ist Heuschnupfen? » Lungenaerzte-im-Netz’, Deutsche Lungenstiftung e.V. und Verband pneumologischer Kliniken e.V., available at https://www.lungenaerzte-im-netz.de/krankheiten/heuschnupfen/was-ist-heuschnupfen/, accessed on 9 June 2020.
 ‘Die Bedeutung der Bestäuber für die Landwirtschaft - Landwirtschaftliche Produktivität und Bestäuberschutz’, available at https://www.europeanlandowners.org/files/pdf/2014/Pollinators_DE_FIN2_LR.pdf, accessed on 9 June 2020.
 ‘Heuschnupfen - Grundlagen’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/krankheitsbilder/heuschnupfen/grundlagen.html, accessed on 4 June 2020.
 ‘Statistics’ Allergy UK, available at https://www.allergyuk.org/information-and-advice/statistics, accessed on 10 March 2021.
 ‘Pollenallergie’, European Centre of Allergy Research Foundation (ECARF), available at https://www.ecarf.org/info-portal/allergien/pollenallergie/, accessed on 9 June 2020.
 ‘Allergies | Symptoms, Diagnosis, Treatment & Management’, The American Academy of Allergy, Asthma & Immunology, available at https://www.aaaai.org/conditions-and-treatments/allergies, accessed on 4 June 2020.
 ‘Heuschnupfen » Risikofaktoren » Lungenaerzte-im-Netz’, available at https://www.lungenaerzte-im-netz.de/krankheiten/heuschnupfen/risikofaktoren/, accessed on 22 June 2020.
 ‘Heuschnupfen - Symptome’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/krankheitsbilder/heuschnupfen/symptome.html, accessed on 10 June 2020.
 ‘Heuschnupfen » Krankheitsbild » Lungenaerzte-im-Netz’, Deutsche Lungenstiftung e.V. und Verband pneumologischer Kliniken e.V., available at https://www.lungenaerzte-im-netz.de/krankheiten/heuschnupfen/krankheitsbild/, accessed 10 June 2020.
 ‘Allergie-Centrum-Charité| Patienteninfo’, Pollenassoziierte Nahrungsmittelallergie, available at https://www.allergie-centrum-charite.de/herzlich-willkommen-zu-den-sprechstunden-br-des-allergie-centrum-charite/nahrungsmittelallergien/patienteninfo/, accessed on 6 June 2020.
 Price, A., Ramachandran, S., Smith, G. P., Stevenson, M. L., Pomeranz, M. K., Cohen, D. E. ‘Oral Allergy Syndrome (Pollen-Food Allergy Syndrome)’, Dermatitis, vol. 26(2), 78–88, Apr. 2015, doi: 10.1097/DER.0000000000000087.
 Ballmer-Weber, B. K. ‘Kutane Symptome nach Genuss pollenassoziierter Nahrungsmittel’, Der Hautarzt, vol. 57(2), article no. 2, Feb. 2006, doi: 10.1007/s00105-005-1077-4.
 ‘Allergene Pflanzen’, Universitätsklinikum des Saarlandes - Innere Medizin V - Pneumologie, Allergologie, Beatmungs- und Umweltmedizin, available at https://www.uniklinikum-saarland.de/de/einrichtungen/kliniken_institute/medizinische_kliniken/innere_medizin_v/patienten_informationen/pollenwarndienst/allergene_pflanzen/, accessed on 9 June 2021.
 ‘Wetter und Klima - Deutscher Wetterdienst - Leistungen - Pollenflug-Gefahrenindex’ available at https://www.dwd.de/DE/leistungen/gefahrenindizespollen/gefahrenindexpollen.html, accessed on 4 June 2020.
 ‘Gewitterasthma’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/aktuelles/schwerpunktthemen/gewitterasthma.html#c189998.
 D’Amato, G., Liccardi, G., Frenguelli, G. ‘Thunderstorm-asthma and pollen allergy’, Allergy, vol. 62(1), 11–16, 2007, doi: 10.1111/j.1398-9995.2006.01271.x.
 Hew, M., Sutherland, M., Thien, F., O’Hehir, R. ‘The Melbourne thunderstorm asthma event: can we avert another strike?’, Internal Medicine Journal, vol. 47(5), 485–487, 2017, doi: 10.1111/imj.13413.
 ‘Heuschnupfen - Diagnose’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/krankheitsbilder/heuschnupfen/diagnose.html, accessed on 11 June 2020.
 ‘Hauttests zur Allergie-Diagnose’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/hauttests.html#c192934, accessed on 11 June 2020.
 ‘Labortests zur Allergie-Diagnose’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/diagnose/labortests.html, accessed on 11 June 2020.
 ‘Heuschnupfen » Vorbeugung » Lungenaerzte-im-Netz’, Deutsche Lungenstiftung e.V. und Verband pneumologischer Kliniken e.V. https://www.lungenaerzte-im-netz.de/krankheiten/heuschnupfen/vorbeugung/, accessed on 11 June 2020.
 ‘Heuschnupfen bei Kindern | kindergesundheit-info.de’, BZgA - Bundeszentrale für gesundheitliche Aufklärung, available at https://www.kindergesundheit-info.de/themen/krankes-kind/erkrankungen/allergien/heuschnupfen/, accessed on 11 June 2020.
 ‘Wie wird Heuschnupfen behandelt?’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/krankheitsbilder/heuschnupfen/therapie.html#c191311, accessed on 11 June 2020.
 ‘Heuschnupfen » Therapie » Lungenaerzte-im-Netz’, Deutsche Lungenstiftung e.V. und Verband pneumologischer Kliniken e.V. https://www.lungenaerzte-im-netz.de/krankheiten/heuschnupfen/therapie/, accessed on 11 June 2020.
 ‘Risiko- und Provokationsfaktoren für die Entstehung von Allergien’, Allergieinformationsdienst - Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt, available at https://www.allergieinformationsdienst.de/immunsystem-allergie/risikofaktoren.html, accessed on 23 June 2020.
 ‘S3-Leitlinie Allergieprävention - Update 2014: Leitlinie der Deutschen Gesellschaft für Allergologie und klinische Immunologie (DGAKI) und der Deutschen Gesellschaft für Kinder- und Jugendmedizin (DGKJ)’, available at https://www.awmf.org/uploads/tx_szleitlinien/061-016l_S3_Allergiepr%C3%A4vention_2014-07-abgelaufen.pdf, accessed on 8 June 2020.