Overview

Asthma is a chronic lung (respiratory) condition caused by inflammation leading to difficulty breathing. People of all ages can be affected, however, symptoms usually start during childhood. In the UK, 5.4 million people are receiving treatment for asthma. The current course of treatment is in the form of inhalers that help resolve symptoms both short and long-term. Unfortunately, there is currently no cure for asthma and symptoms are only managed. The symptoms of asthma can be exacerbated by allergies, which can lead to acute asthma attacks with varying severity.^1,2

The connection between allergies and asthma

What causes an asthma attack?

Currently, the exact cause(s) of asthma remains unknown, but it is associated with both genetic and environmental factors (2). The result of this interaction in people with asthma is inflammation and bronchial vasoconstriction (pronounced: bron-ki-al vase-o-constriction). Common environmental factors such as allergens, viral and bacterial infections, and pollution can exacerbate and lead to an asthma attack in susceptible people.

• What is bronchial vasoconstriction? Bronchioles are smaller ‘tubes’ that connect to the windpipe (trachea). These become tighter during asthma attacks (chest tightness symptom). Though bronchial vasoconstriction is reversible, it can be life-threatening since it reduces the amount of air reaching the lungs causing suffocation if not treated quickly³ 
• And inflammation? Inflammation is the result of the immune system's response to what it recognises as a ‘foreign threat’ that can cause danger to the body. The threat can vary, including allergens, viruses and bacteria. During an asthma attack, the trachea and bronchi become inflamed causing the muscle inside it to tighten. Again, this leads to difficulty breathing⁴

What are allergens and how do they cause an asthma attack? 

The term ‘allergen’ is an umbrella term to describe a substance that can cause an allergic reaction, i.e., activate the immune system causing the production of antibodies leading to the specific immune cells being ‘switched on’.

Immune response

When an allergen first finds its way into the body, it can bind to specific ‘ports’ known as receptors on immune cells (eosinophils, mast cells and basophils). The result of this activation is the release of the specific antibody IgE: a variant involved in hypersensitivity (i.e., priming the immune system for defence). The activated (switched-on) immune cells release chemicals such as histamines that increase inflammation and try to remove the cause of the allergy: the allergen.⁵ 

Histamine release

Histamine released specifically by mast cells and basophils plays a major role in controlling the immune response and the resulting physiological activity. Histamines are found concentrated in the lungs having vasoactive effects (affecting the width of blood vessels). When histamine binds the receptor (‘port’) known as H1 it causes the bronchioles to tighten.⁶

Histamine binding H1 makes the airways more sensitive, and since it affects the smooth muscles in the airways, it causes a narrow spasm and congests the airways with mucus, making it difficult to breathe and leading to an asthma attack. 

Chronic inflammation

Asthma is referred to as a ‘chronic’ inflammatory condition; chronic denoting persistent. Unlike in people without asthma, T-helper type 2 cells (Th2, a type of immune cell) are ready to react to normally harmless allergens such as dust. This heightened activity is thought to be due to a genetic predisposition making these cells more reactive. Therefore, the immune system is regularly in a ‘switched-on’ state.⁷

Common allergens and their effects on asthma

Different types of allergens can lead to an asthmatic episode. 

Indoor allergens

Several different indoor-associated allergens can exacerbate asthma. These allergens can be found at home, in the workplace or in schools. 

• Dust mites: these microscopic critters are found naturally and are not parasites. They feed on dead skin cells. However, dust mites can produce allergens in the form of their droppings that become aerosolized causing potential allergic reactions and asthma in vulnerable individuals⁸
• Mould/mildew: it is estimated that over 2 million people in the U.K. live with mould/mildew in their homes. Spores produced from fungi can lead to hypersensitivity (through the actions of the antibody IgE mentioned earlier), and an asthma episode. Though not all fungi can cause asthma, several are found to do so,⁹ including:
  • Aspergillus 
  • Alternaria
  • Candida
  • Cladosporium 
  • Fusarium
  • Penicillium
• Pet hairs/dander: a commonality in about 57% of households in the U.K. Again, the body recognises microscopic pet hairs as invaders and activates the immune system in the airways, leading to potential asthma attacks in susceptible individuals, exhibiting symptoms such as tight chest and wheezing¹⁰

Seasonal allergens

Pollen is a common seasonal allergen that causes hay fever (runny nose, itchy eyes, sneezing). This same culprit that makes late spring/early summer an itchy sneezy nightmare for many of us can also cause asthma episodes. Studies show that 80-90% of children and 40-50% of adults with asthma, also have pollen-associated allergies, with many suffering from acute asthma attacks when the pollen count is high. 

Pollutants

For most of us who live in an urban, or even suburban setting, it can be hard to escape the constant air pollution. Sources of these include: 

• Exhaust fumes from vehicles: diesel fuel particularly has been found to stimulate the activation of Th-lymphocytes, which are already on heightened alert in people with asthma¹¹
• Dust is a common aggregator of asthma, especially when in high quantities¹¹ 
• Industrial factories including mining, oil production, and subsequent large transportation of goods can produce air pollutants in the form of sulphur dioxide, nitrogen dioxide and methane.¹¹ These can exacerbate pre-existing asthma

Clinical studies and evidence

Studies linking allergies and asthma exacerbations

Numerous studies link the interaction between allergens and the increased likelihood of asthma exacerbation. 

• A study undertaken in 10 European cities found that 14% of cases of acute asthma in children and 15% of all childhood asthma exacerbations were directly a cause of air pollution from road traffic 
• Other studies have linked genetic predispositions to the likelihood of asthma exacerbation following exposure to air pollutants. For example, one study found that mutations in genes that provide the necessary defence against reactive chemicals produced when pollutants are inhaled, lead to an increased likelihood of asthma exacerbations when these pollutants are encountered
• There are extensive studies dating back to the 1980s showing that exposure to ozone (a form of oxygen) and sulphur dioxide results in inflammation of the airways

Management of allergies to reduce asthma exacerbation

Though there is currently no cure for asthma, there are a variety of treatment options that can help alleviate symptoms: both acute and chronic. 

Medical interventions

There are a number of medical-related treatments including: 

• Inhalers: the most common and widely recognised treatment of asthma. There are two types of inhalers one might commonly use for asthma:¹²
  • Reliever inhalers are used to reduce symptoms following an asthmatic episode. These are usually blue in colour. There are short term side-effects including shakiness and increased heart rate after the inhaler is used, but these disappear soon after
  • Preventer inhalers are to stop the development of symptoms. These inhalers contain medical steroids and are prescribed by a GP (or medical professional) due to the potential side effects including oral thrush (fungal infections of the mouth), hoarse voice, and sore throat- though these can be uncommon
  • Combination inhalers (as the name suggests) are a combination of both reliever and preventer inhalers. These are used when individual inhalers are not preventing asthma attacks as well. These are used daily. The side effects associated are the same as the reliever and preventer inhalers
• Tablets are also a potential method of treatment if inhalers alone are not effective.
  • Theophylline is used to prevent and treat wheezing, chest tightness and shortness of breath caused by asthma
  • Steroid tablets can be used either as an immediate treatment for an asthma attack or as a long-term preventative treatment. Prednisone is the most commonly prescribed and results in reduced inflammation⁷
  • Antihistamine tablets can be used as an allergy relief and reduce asthma exacerbations. These can be obtained over the counter, but ensure to follow usage suggestions supplied by the provider

Complementary therapies

• Breathing exercises such as:
  • Buteyko method: breathing through the nose instead of the mouth and reducing the volume of air taken in. This method can help reduce tightness of the chest and improve breathing
  • Papworth method: this technique relies on diaphragm breathing and relaxing exercises that can help strengthen breathing muscles and reduce discomfort during asthmatic episodes 
• Regular aerobic exercise and time away from polluted spaces can also help reduce asthmatic severity
• Avoiding sources of exacerbation such as smoking significantly reduced asthmatic episodes

Future research and considerations

Much about the aetiology (genetic and physiological causes) of asthma remains unknown despite the great strides made over decades of research. 

Future research aims to explore and resolve the development of asthma. Asthma commonly occurs during childhood and research is ongoing to distinguish the genetic causes that lead to its development.  For example, clinical trials are underway to understand how different genes affect immune cells in asthma, and potential ways it can be corrected using therapeutics. 

On top of the progressive scientific work done to learn more about asthma, the growing problems of asthma in people have been recognised and has increased awareness leading to alterations to urban environments through increased planting of trees, introduction of ultra-low emission zones (e.g., in London, U.K.), and the reduction of diesel car sales. All of which positively contribute to better breathing. 

Summary

Asthma is a global health crisis affecting millions of people. This chronic respiratory condition causes shortness of breath, dizziness, and difficulties undertaking daily activities that may exacerbate symptoms. Common allergens are a source of exacerbation through activation of the immune system resulting in episodic asthma attacks. Asthma currently has no cure but is commonly treated with inhalers that reduce or prevent symptoms. Research has shown potential genetic links, but further research is ongoing to develop potential cures. Recent urban amendments to pollutants and laws to reduce the impact of pollution have aided individuals suffering from asthma. 

FAQs

Who should I reach out to if I am suffering from asthma? 

• Asthma+Lung UK
• NHS
• Your GP or medical practitioner

Does allergy-induced asthma go away?

Unfortunately, you don’t out-grow asthma and therefore allergy-induced asthma. But, as we get older (remember asthma often starts during childhood) the airways become larger and the symptoms can subside. 

Do antihistamines help with asthma exacerbation? 

Though they are not the first line of treatment for asthma, they can help alleviate symptoms of allergy-induced asthma.