What Is Pollen Allergy

Pollen allergy

The presence of green spaces in urban areas is essential for reducing air pollution levels and air temperature. As the winter transitions to spring, flowers bloom, trees start budding and growing leaves. Besides flowers, pollen is also found in weeds, grass and trees, but they are small and dry so they can easily disperse into the wind. This pollen production is essential for the reproduction of flowers and plants during the warm seasons. However, despite its ecological benefits, pollen can cause problems for humans by triggering allergic reactions. So why is it important to find out more about pollen allergy?¹

Prevalence 

Nowadays, the prevalence of pollen allergy is increasing. Studies have shown that the causes for this increase are due to the rise of urbanisation, climate change and air pollution, particularly in urban areas. Pollen normally causes allergic rhinitis, and its prevalence has mainly increased in developed cities and countries, affecting 10-30% of adults and 20-25% of children worldwide. This allergy has a considerable effect on the quality of life of pollen allergy sufferers.²

Importance

To reduce the effects of air pollution and climate change, an increase in green spaces and urban forests has been introduced to improve the lifestyle of living in urban areas. However, increasing green spaces could impact the increased prevalence of pollen allergy. It is, therefore, necessary to understand how pollen allergy develops and how it can be prevented and treated.²

Types of pollen allergies

Tree pollen allergy

Here are some common tree pollen allergens that are found in the environment:

• Birch tree - Around 19.6% of Europeans suffer from birch tree pollen allergy caused by the Bet v 1 protein found in birch tree pollen.
• Plane tree - Originally from the Northern Hemisphere, the plane tree is also found in Asia and European countries. The plane tree pollen is known to affect 12% of the UK population. The Pla, an inhibitor in the birch tree pollen, is responsible for triggering an allergic reaction. 

Grass pollen allergy

Besides tree pollen, common grass pollen allergens are fairly common in the outdoors and have a high chance of being exposed to humans.

• Timothy grass - Found in temperate climates and affecting around 18.5% - 28.5% of the European population, timothy grass allergy is predominantly caused by the Phl p 1 and Phl p 5 allergens, affecting around 90% of the grass pollen allergic patients.
• Bermuda grass - Bermuda grass allergy is caused by the Cyn d 1 allergen, and this type of grass allergy is found in 76% of patients with grass pollen allergies. 
• Bahia grass - Pas n 1 allergen has also been found to be causing grass pollen allergy.

Weed pollen allergy

Similar to both grass and tree pollen, several weed pollens can trigger an allergic reaction.

• Ragweed - Found in Central and Northern America, ragweed allergy is caused by the Amb a 1 allergen 
• English plantain - English plantain pollen is ubiquitous in flower seasons. They are found in Central and Southern areas of Europe and the the Pla l 1 allergen in English plantain is responsible for eliciting an allergic reaction. 
• Mugwort - Found in the Northern Hemisphere, mugwort-specific pollen allergy is found to affect 10%-14% of patients in the European population. This type of weed allergy is caused by the Art v 1 allergen.³

Causes and triggers

How do pollen allergies develop?

When an allergic reaction happens, the body’s immune system reacts to a particular unfamiliar property (allergen)  that is not harmful to the body. The immune system will treat these allergens as germs or foreign substances that need to be neutralised and removed from the body. For example, dust and certain foods like nuts and shellfish, which normally will not cause you harm, could activate the immune system of those who are allergic to dust and food. An allergic reaction happens when the immune system forms antibodies, also known as IgE, which recognise the allergen and trigger an immune response when immune cells detect the antibodies. These antibodies act like a tag when lined to the allergen, alerting the immune system to the presence of a foreign object in the body and the need to eliminate it immediately. To form IgE antibodies, the body must come first in contact with the foreign allergens and remember it through a process called sensitisation. However, the immune system will not do anything until the body is exposed to the allergens again. So if the body comes in contact with the allergens again, a chemical substance made by the immune system known as histamines will be released. This will then contribute to the manifestation of various allergic symptoms, such as sneezing, skin rashes and coughing.^4,5

Genetics and environmental factors

This condition is known to be an atopic condition, which means it may often run in the family. This suggests that genetics are involved in the manifestation of allergy. However, whether or not a person develops a pollen allergy depends mainly on environmental factors. For example, the weather, pollution, humidity, wind speed direction and location.⁶

Symptoms of pollen allergy

Pollen allergy symptoms can occur throughout the year. However, they can become worse in spring, summer and early autumn. This is because warmer conditions promote weeds and flowers to bloom, so pollen count will increase in the air.

Common symptoms:

• Nasal Congestion, runny nose, sneezing
• Itchiness in eyes, nose and throat
• Increased mucus in throat and nose
• Headaches, sinus pain
• Fatigues and tiredness/discomfort, dark circles under the eyes
• Wheezing, coughing, breathing problems
• Sore throat, postnasal drip⁷

Complications

Allergies are mostly mild at first; however, depending on the severity of the symptoms, they can lead to more severe medical conditions. For example, if you have prolonged pollen allergies, then there is a chance of you developing asthma later in life. Another example is skin rashes from an allergic response that becomes more severe, and then you can also develop a skin condition known as eczema.⁸

Diagnosis 

There are several ways pollen allergies can be diagnosed:

Allergy testing methods

1. Skin Prick Tests: A doctor or nurse will place a small drop of the allergen on the skin by prickling or scratching the surface of the skin with a needle. If you have IgE antibodies towards the allergen, the spot that has been pricked will become red, followed by some itching and swellings after  15-20 minutes. This phenomenon is called a wheal and flare reaction. If the wheel grows, then you are likely to be allergic to the allergen.
2. Blood Tests: The radioallergosorbent test (RAST)  is a type of blood test that can help diagnose a skin condition or be used on children who may find the skin prick test scary. The doctor first takes a blood sample and sends it to the laboratory for testing. The laboratory will then add the allergen to the blood sample and measure the amount of antibodies released in the blood sample.⁸

Differential diagnosis

Another differential diagnosis method that can help with the diagnosis of pollen allergy is molecular diagnostics. This technique utilises purified versions of the allergens from natural sources and recombination molecules. This allows healthcare professionals to get detailed information on the sensitisation process needed for the management of pollen allergy.²

Treatment and management

Avoidance strategies

• Taking allergy medication before the pollen season prevents the body from releasing histamine and various biochemicals that cause allergic symptoms.
• Limiting outdoor activities when there is a high pollen count can help to manage symptoms.
• Keeping windows closed prevents pollen from entering enclosed spaces.
• Wearing sunglasses and covering hair keeps the pollen out of the eyes and hair.
• Washing beddings frequently can remove pollen and reduce exposure.
• Limit contact with pets - pets can carry pollen in their fur, so limiting this can aid in less spreading of pollen.
• Staying informed on the pollen count for the day and at what time the pollen count is the highest via local weather reports can help prevent unnecessary exposure to pollen.⁸

Medications

1. Antihistamines

Antihistamines are medications that suppress the effects of histamine. They come in liquid, nasal spray or pill form. Antihistamines are commonly taken to relieve sneezing and frequent itching of the nose and the eyes. They can also temporarily stop a runny nose and nasal stuffiness. Examples of antihistamines include Allegra, Claritin Alavert and Zyrtec.

1. Decongestants 

Decongestants can help shrink the swollen nasal passage lining triggered by an allergic reaction to relieve stuffiness. It is usually used for only a short period of around 3 days. The use of decongestants should be consulted with the doctor if you have glaucoma, high blood pressure and thyroid disease. Examples of decongestants include Vicks Sinex, Sudafed, Actifed and many more. 

1. Corticosteroids

Corticosteroids usually come as nasal sprays. They help treat inflammation around the lining of the nose because they mimic the effects of cortisol. Examples of this medication include Flonase Allergy Relief, Nasonex, and many more.⁹ 

Immunotherapy (allergy shots) 

Allergy shots are a type of immunotherapy that helps to prevent allergic reactions and make them easier to manage. This treatment can alter the trajectory of pollen allergy by modifying the body's immune response to the allergens. 

Allergy shots are also known as subcutaneous immunotherapy (SCIT). It is a treatment that has been used for 100 years and has the potential to reverse an allergic reaction rather than just treat allergic symptoms. This involves injecting an allergen into the fatty layer under the skin, enabling the patient to overcome allergic symptoms. These results may only last for 1 to 3 years after stopping  SCIT.⁸

Emergency treatment (Anaphylaxis)

Pollen and various allergens rarely cause anaphylaxis, however, it can happen if your symptoms are very severe and left untreated. Anaphylaxis can be life-threatening and requires immediate medical attention. The beginning of anaphylaxis from an allergic reaction can manifest as severe throat itching, followed by difficulty in breathing due to rapid swelling of the throat and windpipe.¹⁰

Lifestyle tips for pollen allergy sufferers

There are some ways in which you can help manage your symptoms by controlling the amount of pollen present in your home. This includes installing an air conditioner or an air cleaner with HEPA filtration or an allergy filter. These filters help eliminate 99.97% of the dust and pollen that enters your home. However, this equipment can be very expensive and requires regular maintenance. ¹¹

Future developments and research

At present, the best approach for treating the root cause of pollen allergy is immunotherapy.  Despite the progress made in allergy treatment by introducing the use of recombinant allergens to help with a more precise diagnosis of the type of allergy, studies have shown that recombinant allergen immunotherapy does not have an advantage over the efficacy and safety of using allergen extracts. However,  the use of recombinant allergens is being researched for producing bespoke vaccines that contain specific allergens that are based on the specified IgE sensitivity.¹¹

Summary

Pollen allergy is becoming more and more common in humans as a result of increased exposure to pollution and urbanisation. Symptoms of pollen allergy can range from itchy eyes to more severe conditions such as eczema. In non-life-threatening cases, pollen allergy symptoms can be managed by the use of over-the-counter medications like antihistamines and decongestants or simply by reducing the time of outdoor activities. Subcutaneous immunotherapy is a long-term treatment option that can reduce the severity of allergic reactions to pollen, though this treatment method will only last for 1-3 years after treatment cessation. With ongoing research in the development of allergen vaccines using recombinant allergens, there is hope that pollen allergy can be cured or prevented completely.