Allergies, a result of the immune system's overreaction to typically harmless substances, can range from mild symptoms like sneezing to life-threatening anaphylaxis. Below article provides an overview of allergy triggers, mechanisms, and emerging treatments, all informed by the latest research and clinical advancements.

Why do some people have allergies?

Genetic Factors

Specific genes associated with immune regulation and inflammatory responses can significantly increase an individual's susceptibility to developing allergies.

Epigenetic Influences

It's important to be aware of how environmental factors can influence gene expression through epigenetic modifications, potentially altering an individual's susceptibility to allergies or even across generations.

Hygiene Hypothesis

This theory suggests that reduced exposure to microbes in early life due to improved hygiene may lead to an underdeveloped immune system, increasing the risk of allergies.

Environmental Pollutants

Exposure to air pollution and other environmental toxins may increase the risk of developing allergies by altering immune system function.

Allergen Properties 

Specific proteins in allergens have structural characteristics(molecular structure) that make them more likely to trigger an allergic response. These include stability, size, and the ability to cross epithelial barriers.

Cross-Reactivity

Some allergens share similar protein structures, leading to cross-reactivity, in which an individual allergic to one substance may react to others with similar molecular structures.

Immune System Imbalance

Th1/Th2 Balance

Allergies are associated with an imbalance between T helper 1 (Th1) and T helper 2 (Th2) immune responses, with a shift towards Th2 dominance promoting allergic reactions.

Regulatory T Cell Dysfunction

The impaired function of regulatory T cells, which generally help maintain immune tolerance, can contribute to the development of allergies.

Common allergens 

Allergens vary widely and can be grouped into environmental, food, and contact categories:  

Environmental allergens

• Airborne(via air): Pollen, dust mites, mould spores, and pet dander
• Insect-related: Bee or wasp stings, cockroach debris
• Irritants: Cigarette smoke, perfume, car exhaust

Food Allergens  

• Top triggers: Peanuts, tree nuts, milk, eggs, shellfish, soy, wheat, fish, and sesame
• Childhood prevalence: Milk and egg allergies are most common in infants, while peanut allergies often persist into adulthood 

Other Triggers 

• Medications (e.g., penicillin), latex, and certain chemicals 

Immune Mechanism of Allergies  

Allergies occur when the immune system mistakenly identifies harmless substances as threats. Upon initial exposure to an allergen, the body produces specific immunoglobulin E (IgE) antibodies.¹ These antibodies attach to immune cells like mast cells and basophils, priming the immune system for future encounters. Understanding the mechanisms, diagnosis, and treatment options for allergies is crucial for effective management and improving the quality of life for those affected.

Allergic reactions primarily involve Type I hypersensitivity, mediated by IgE antibodies:  

• Sensitisation: Initial allergen exposure prompts B cells to produce IgE antibodies, which bind to mast cells and basophils 
• Re-exposure: Allergen cross-links IgE on sensitised cells, triggering the release of histamine, leukotrienes, and cytokines
• Symptoms: Rapid onset of itching, swelling, hives, or anaphylaxis due to systemic inflammation

Altered immune system processes in an allergic patient

Histamine Release and Symptoms

When re-exposed to the allergen, IgE antibodies trigger mast cells and basophils to release histamine and other inflammatory mediators.¹ This release causes the characteristic symptoms of allergies, such as sneezing, itching, and nasal congestion. The severity of symptoms can vary widely among individuals and allergens.

Anaphylaxis

In some cases, allergic reactions can be severe and life-threatening, leading to anaphylaxis. This systemic reaction can cause rapid onset of symptoms affecting multiple organ systems, including difficulty breathing, swelling of the throat, and a dangerous drop in blood pressure.²

Diagnosis of Allergies

Symptoms and Clinical Assessment

Diagnosing allergies begins with a thorough clinical assessment. Common symptoms include sneezing, runny nose, itchy eyes, and skin rashes. The timing and consistency of symptoms with allergen exposure are crucial factors in diagnosis.³

Testing Methods

Several methods are used to diagnose allergies:

• Skin prick tests: Small amounts of allergens are introduced into the skin to observe local reactions
• Blood tests: Specific IgE levels are measured to identify sensitisation to particular allergens¹
• Oral food challenges: Used to definitively diagnose or rule out food allergies³

Challenges in Diagnosis

Diagnosing allergies can be challenging due to overlapping symptoms with other conditions. Non-IgE-mediated allergies, such as specific food allergies, may present with delayed symptoms, making diagnosis more complex.⁴

Traditional Treatment Options

Antihistamines

Antihistamines are commonly used to manage mild to moderate allergy symptoms by blocking the effects of histamine.⁵

Corticosteroids

Nasal corticosteroid sprays and oral steroids are effective in reducing inflammation and managing more severe allergic reactions.⁵

Allergen Avoidance

Identifying and avoiding specific allergens is crucial to allergy management, particularly in food and environmental allergies.⁴

Immunotherapy

Allergen-specific immunotherapy, such as allergy shots, can help desensitise the immune system to specific allergens, providing long-term relief for some individuals.⁵

New and Emerging Allergy Treatments

Biologic Drugs

Monoclonal antibodies, such as omalizumab, target specific components of the allergic response, offering new treatment options for severe allergies.⁵ Targeted therapies (e.g., anti-IgE monoclonal antibodies) block specific immune pathways involved in allergic responses.⁶ 

Allergen Immunotherapy Innovations

New forms of immunotherapy, including sublingual tablets and subcutaneous injections, are being developed to improve efficacy and patient compliance.⁵

Probiotics and Microbiome Research

Research is exploring the role of gut health and the microbiome in allergic diseases, with potential for new therapeutic approaches.⁵

Future Directions

Personalised Medicine for Allergies

Genetic and molecular research advancements are paving the way for personalised allergy treatments based on individual patient profiles.⁵

Ongoing Research

Current clinical trials are investigating novel approaches to allergy treatment, including targeted therapies and potential allergy vaccines.⁵

Gene therapy

 Investigational approaches aim to edit genes responsible for allergic sensitisation.  

Cell Therapy  

Mesenchymal Stromal Cells (MSCs): These cells modulate immune responses by suppressing Th2 activity (linked to allergies) and promoting regulatory T cells, promising to reduce airway inflammation and eczema.⁶  

Advances in Allergen Detection and Monitoring

Smart devices and apps are being developed to help individuals monitor their allergen exposure and manage their symptoms in real time.⁵

Conclusion

Allergies remain a significant health concern affecting millions worldwide. Early detection, accurate diagnosis, and personalised treatment approaches are crucial for effective management. As research continues to uncover the complex mechanisms underlying allergic reactions, new and innovative treatments are emerging, offering hope for improved outcomes and quality of life for allergy sufferers. The future of allergy management lies in personalised medicine, targeted therapies, and advanced monitoring technologies, promising more effective and tailored approaches to allergy care.