Background

Allergic rhinitis, commonly known as hay fever, is an allergic reaction when the immune system overreacts to environmental allergens. It is a common condition that affects a significant portion of the population worldwide. Seasonal allergic rhinitis, also known as hay fever, occurs during specific seasons when certain plants release pollen into the air.

Common triggers include tree pollen in spring, grass pollen in summer, and weed pollen in fall. Perennial allergic rhinitis is a type of allergic rhinitis that persists throughout the year and is usually caused by indoor allergens such as dust mites, pet dander, mold, or cockroach allergens.

Epidemiology

Allergic rhinitis is a common condition, and its prevalence varies across different populations and geographical locations. According to estimates, allergic rhinitis affects approximately 10-30% of adults and up to 40% of children worldwide. The prevalence can be higher in urban areas and industrialized countries. The incidence of allergic rhinitis refers to the rate of new cases developing within a specific period. It can vary depending on age, genetics, environmental exposure, and geographical location.

The incidence tends to be higher in children and adolescents, with the condition often developing during early childhood. Specific allergens in the environment primarily trigger seasonal allergic rhinitis during certain seasons. Different types of pollen can cause symptoms during different times of the year. For example, tree pollen allergies are more common in spring, grass pollen allergies in summer, and weed pollen allergies in fall.

However, it’s important to note that perennial allergic rhinitis, triggered by indoor allergens, can occur year-round and is not limited to specific seasons. Allergic rhinitis can affect both males and females, but some studies suggest it may be more prevalent in males during childhood. In contrast, females may have a higher prevalence during adulthood. The reasons for these gender differences are not yet fully understood and may involve complex interactions between genetic, hormonal, and environmental factors.

Anatomy

Pathophysiology

Sensitization is the initial step in the development of allergic rhinitis. It occurs when an individual is first exposed to an allergen, such as pollen or dust mites. The allergen enters the body, typically through inhalation, and comes into contact with immune cells called antigen-presenting cells (APCs). The APCs process the allergen and present it to another type of immune cell known as a T-lymphocyte (T-cell). The T-lymphocytes, specifically a subset called T-helper 2 (Th2) cells, recognize the allergen presented by the APCs. Upon activation, the Th2 cells release chemical signals called cytokines, particularly interleukin-4 (IL-4), interleukin-5 (IL-5), and interleukin-13 (IL-13).

These cytokines play a crucial role in orchestrating the subsequent immune response. IL-4 stimulates B-lymphocytes to produce and release large amounts of immunoglobulin E (IgE) antibodies specific to the allergen. IgE antibodies are specialized molecules that bind to mast cells and basophils, which are types of immune cells found in tissues throughout the body, including the nasal passages. During subsequent exposures to the same allergen, the allergen binds to the specific IgE antibodies attached to the mast cells and basophils.

This triggers the release of various chemical mediators from these cells, such as histamine, leukotrienes, and prostaglandins. Releasing chemical mediators leads to an inflammatory response in the nasal mucosa. Histamine causes blood vessels to dilate, leading to nasal congestion and swelling. It also triggers itching and stimulates the production of mucus. Leukotrienes and prostaglandins contribute to increased mucus production, bronchoconstriction, and further inflammation.

Etiology

The etiology of allergic rhinitis involves a combination of genetic predisposition and environmental factors.

• Genetic Factors: There is a significant genetic component to allergic rhinitis. If one or both parents have allergic rhinitis, asthma, or other allergic conditions, the risk of a child developing allergic rhinitis increases. Specific genes related to the immune system and the body’s response to allergens are thought to play a role in the development of allergic rhinitis.
• Allergen Exposure: Allergic rhinitis is triggered by exposure to specific allergens, which vary among individuals. Common allergens include pollen from trees, grasses, weeds, dust mites, pet dander, mold spores, and certain foods. When a susceptible individual comes into contact with these allergens, the immune system overreacts, leading to allergic symptoms.
• Immune System Dysregulation: Individuals with allergic rhinitis have an immune system hypersensitive to allergens. Upon exposure to allergens, the immune system reacts by producing IgE antibodies specific to those allergens. This immune response releases various chemical mediators, causing inflammation and the characteristic symptoms of allergic rhinitis.
• Environmental Factors: Environmental factors can contribute to the development and severity of allergic rhinitis. These include air pollution, tobacco smoke, occupational exposures to allergens or irritants, and early-life exposures such as breastfeeding practices, exposure to allergens during infancy, and exposure to certain infections or antibiotics during childhood. These factors can influence the immune system’s development and response to allergens.
• Hygiene Hypothesis: The hygiene hypothesis suggests that reduced exposure to microbes and certain infections in early childhood may increase the risk of developing allergic conditions, including allergic rhinitis. According to this hypothesis, a lack of exposure to microbes and infections during critical periods of immune system development may lead to an imbalance in immune regulation, resulting in an increased risk of allergic diseases.

Genetics

Prognostic Factors

The prognosis of allergic rhinitis is generally good as it is a chronic condition that can be managed effectively with appropriate treatment and lifestyle modifications.

Clinical History

A comprehensive and detailed medical history is crucial in assessing allergic rhinitis (AR). It is important to ask specific questions about the nature of symptoms, their timing, duration, and frequency, any potential exposures, factors that worsen or alleviate symptoms, and any observed seasonal patterns.

Individuals with intermittent or seasonal AR commonly experience sneezing, rhinorrhea, and watery eyes. On the other hand, patients with chronic AR often present with complaints of postnasal drip, persistent nasal congestion, and obstruction. These individuals frequently have a family history of allergic rhinitis or a personal history of asthma.

Patients with intermittent rhinitis may provide information about triggers that initiate their symptoms, including allergens like pollen, animal dander, mold, dust mites, and irritants such as certain flooring or upholstery materials, high humidity levels, strong perfumes, or exposure to tobacco smoke.

Physical Examination

While the diagnosis of allergic rhinitis is primarily based on clinical history, physical examination findings can provide additional information. The provider may observe nasal congestion or swelling of the nasal passages. The presence of clear, watery nasal discharge (rhinorrhea) may be noted. The provider may observe redness or swelling of the conjunctiva, the thin membrane covering the white part of the eyes.

Excessive tearing or watery eyes (epiphora) may be noted. Signs of postnasal drip and mucus dripping down the back of the throat can be observed. This can lead to throat irritation or cough. Dark circles or puffiness under the eyes, known as allergic shiners, may be present due to congestion of blood vessels in the area.

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Vasomotor Rhinitis

Infectious Rhinitis

Nasopharyngeal Neoplasm

Nasal Polyposis

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

Identify and try to avoid allergens that trigger your symptoms. This may involve taking steps such as using dust mite-proof covers on bedding, keeping windows closed during high pollen seasons, and avoiding outdoor activities when pollen counts are high.

Medications such as antihistamines, nasal corticosteroids, and leukotriene receptor antagonists are commonly prescribed. Also, rinsing the nasal passages with a saltwater solution can help reduce nasal congestion and remove allergens and thin mucus.

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Medication

Future Trends

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References