Allergic rhinitis, also known as hay fever, is characterised as inflammation of the nose due to an overreaction of the immune system to allergens (substances that enter the body through the nose to trigger a reaction)¹. Common examples of allergens include as pollen, dust or animal fur.

Evidence suggests that allergic reactions are caused by a combination of both genetic and environmental factors, with a genetic predisposition in individuals with a family history of atopic diseases like asthma and eczema^2,4. The condition can develop begin at any age, although most people first develop symptoms in childhood or young adulthood².

Types of allergic rhinitis:

There are two types of allergic rhinitis; seasonal allergic rhinitis (SAR) and perennial allergic rhinitis (PAR)³.

Seasonal allergic rhinitis (SAR)

Symptoms develop during specific seasons such as spring, summer and early Autumn. Allergens that cause this type of rhinitis include pollens from trees, grasses, and weeds^3,4.

Perennial allergic rhinitis (PAR)

Symptoms persist throughout the year and is difficult to diagnose as the symptoms can mimic sinusitis or respiratory infections². Allergens that cause this type of allergic rhinitis include dust mites, cockroaches, animal dander, and fungi or mould^3,4.

How does allergic rhinitis develop?

During allergic rhinitis, an allergen enters the nose and penetrates your nasal mucosa (the lining of your inner nasal cavity), where it binds to the IgE antibodies on the surface of immune cells (mast cells). In a normal person, this process is minimal but in a person suffering from allergic rhinitis the process is excessive, resulting in the release of histamine^1,4.

Histamine causes inflammation and swelling of the nasal mucosa, excessive mucus production and blood vessel dilation. Excessive mucus production results in rhinorrhoea (runny nose) and blockage the nasal lacrimal duct (tear duct) resulting in water eyes and blockage of the eustachian tubes resulting in the sensation of blocked ears. Finally, the nerves in the nasal cavity may become irritated resulting in sneezing¹.

In summary allergic rhinitis may result in 5 main symptoms¹:

• Nasal swelling and congestion
• Water eyes
• Blocked ears
• Runny nose
• Sneezing

References:

1. http://www.worldallergy.org/professional/allergic_diseases_center/rhinitis/rhinitis_indepth.php
2. https://www.ncbi.nlm.nih.gov/pubmed/11449200
3. http://acaai.org/allergies/types/hay-fever-rhinitis
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1661616/

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