Allergic rhinitis

Allergic rhinitis is an inflammatory condition of the nose that happens when the immune system overreacts to airborne allergens. The seasonal form is known as hay fever, and it is considered a type I hypersensitivity reaction. Common symptoms include a runny or stuffy nose, sneezing, red, itchy, and watery eyes, and swelling around the eyes. Nasal discharge is typically clear.

Symptoms usually appear within minutes of encountering an allergen and can interfere with sleep, work, or study. For some people, symptoms occur only during certain seasons, often due to pollen. Many individuals with allergic rhinitis also have asthma, allergic conjunctivitis, or atopic dermatitis.

Prevention

The condition is usually triggered by environmental allergens like pollen, pet dander, dust mites, or mold. Both inherited genetics and environmental exposures play a role in developing allergies. Growing up on a farm or having multiple older siblings is linked to a lower risk. The underlying process involves IgE antibodies binding to an allergen, which then triggers mast cells to release inflammatory chemicals such as histamine.

This causes the mucous membranes in the nose, eyes, and throat to become inflamed and itchy as the body tries to expel the allergen. Diagnosis is typically based on symptoms along with a skin prick test or blood tests for allergen-specific IgE antibodies, though these tests can produce false positives. Allergic rhinitis symptoms resemble those of the common cold, but they often last longer than two weeks and usually do not include a fever.

Early exposure to animals may reduce the risk of developing these allergies. Several types of medications can help, including nasal steroids, intranasal antihistamines like olopatadine or azelastine, second-generation oral antihistamines such as loratadine, desloratadine, cetirizine, or fexofenadine, the mast cell stabilizer cromolyn sodium, and leukotriene receptor antagonists like montelukast. However, medications often do not fully control symptoms and can have side effects.

Allergen immunotherapy, which involves exposing people to gradually larger amounts of the allergen, is often effective and is used when first-line treatments fail. The allergen can be given as an injection under the skin or as a tablet under the tongue. Treatment usually lasts three to five years, after which benefits may continue.

Epidemiology

Allergic rhinitis is the most common type of allergy. In Western countries, it affects 10 to 30% of people each year, most often between the ages of twenty and forty.

History

The first accurate description came from the 10th-century physician Abu Bakr al-Razi. In 1859, Charles Blackley identified pollen as the cause, and in 1906, Clemens von Pirquet determined the mechanism. The term "hay fever" originated from an early, incorrect theory that symptoms were caused by the smell of new hay.

Signs and symptoms

Characteristic symptoms include excess nasal secretion, itching, sneezing fits, and nasal congestion. Physical signs can include conjunctival swelling and redness, eyelid swelling with Dennie–Morgan folds, dark circles under the eyes from lower eyelid venous stasis (called "allergic shiners"), swollen nasal turbinates, and middle ear effusion. Nasal endoscopy may reveal pale, boggy inferior turbinates from mucosal edema, stringy mucus in the nasal cavities, and cobblestoning. Behavioral signs include the "nasal salute" or "allergic salute," where people rub their nose upward with their palm to relieve irritation or mucus flow.

This can create a transverse nasal crease and, if repeated often, lead to permanent deformity. Cross-reactivity is also possible; for instance, people allergic to birch pollen may react to apple or potato skin, causing an itchy throat or sneezing. Hay fever is not a true fever and does not raise core body temperature above 37.5–38.3°C.

Predisposing factors include eczema and asthma; these three conditions often occur together as the atopic triad. Environmental exposures like air pollution and maternal tobacco smoking can also increase the risk.

Seasonal allergic rhinitis, commonly called hay fever, is triggered by pollens from wind-pollinated plants, which are tiny and easily airborne. Pollens from insect-pollinated plants are too large to stay airborne and pose no risk. Examples of common pollen sources include trees such as pine, mulberry, birch, alder, and cedar.