Hay fever, medically called allergic rhinitis when it is caused by airborne allergens, is an allergic inflammatory condition affecting the nose and often the eyes. In the UK, seasonal hay fever is most commonly triggered by pollen from grasses, trees or weeds. Typical symptoms include sneezing, an itchy or runny nose, nasal congestion, itchy or watery eyes and an itchy throat or palate. Despite its name, hay fever is not caused by hay and does not involve a fever. The historical name arose because symptoms were associated with the haymaking season, when airborne plant material and pollen were abundant.
Allergic rhinitis occurs when the immune system reacts excessively to otherwise harmless airborne proteins. In an IgE-mediated reaction, exposure to an allergen activates mast cells and other immune pathways in the nasal and ocular tissues. Histamine and other inflammatory mediators produce itching, sneezing, vasodilation, increased mucus secretion and tissue swelling. This explains the characteristic combination of watery nasal discharge, repeated sneezing and congestion. The reaction can occur within minutes of exposure and can persist while exposure continues.
Hay fever can be seasonal or perennial. Seasonal allergic rhinitis occurs during periods when relevant pollen is present, with timing varying according to plant species, weather and geographical location. Tree pollen often appears earlier in the year, grass pollen later in spring and summer, and weed pollen at different times depending on species and region. Perennial allergic rhinitis is triggered by allergens present throughout the year, such as house-dust mites, moulds or animal allergens, although this is usually distinguished from seasonal pollen-related hay fever.
Symptoms commonly affect the upper respiratory tract and eyes. Nasal symptoms include itching, sneezing, clear watery discharge and congestion. Ocular symptoms include itching, redness and watering, a pattern known as allergic conjunctivitis when the eyes are significantly involved. Some people experience coughing or worsening of asthma symptoms because allergic inflammation can affect the lower airways. Headaches or facial pressure can occur, especially with severe nasal obstruction, but severe facial pain, high fever or thick persistent discharge can point towards another condition such as infection rather than uncomplicated hay fever.
Hay fever is different from a common cold. Colds are infectious illnesses caused by viruses and commonly produce sore throat, cough, malaise and sometimes fever, whereas allergic rhinitis usually causes itching, repeated sneezing, watery discharge and symptoms that correlate with allergen exposure. Hay fever is not contagious. Symptoms can nevertheless overlap, and a person can have both an infection and allergic rhinitis. The absence of fever does not alone prove an allergy, but the pattern and seasonal recurrence provide useful clues.
Pollen exposure varies according to plant type, weather and location. Warm, dry and windy conditions can increase airborne pollen concentrations, while rain can temporarily reduce airborne pollen although thunderstorms and changing weather patterns can have more complicated effects. Pollen can enter homes through open windows, clothing and hair. People with significant symptoms may therefore notice differences according to where they spend time and the prevailing pollen conditions. Weather-based pollen forecasts can help some people anticipate high-exposure periods.
Hay fever is common and can significantly affect quality of life even though it is usually not dangerous. Poor sleep caused by nasal obstruction can lead to daytime tiredness, while persistent symptoms can interfere with concentration, school, work and outdoor activities. People with asthma may also experience worsening respiratory symptoms during pollen exposure. Severe breathing difficulty should not be automatically attributed to hay fever, however, because it can indicate asthma or another respiratory problem requiring assessment.
Management combines allergen avoidance where practical with medicines that reduce inflammation or symptoms. Antihistamines can reduce itching, sneezing and watery symptoms, while corticosteroid nasal sprays are particularly effective for nasal inflammation and congestion when used correctly and consistently. Saline nasal irrigation can help some people, and severe persistent cases may be considered for allergen immunotherapy by specialist services. Hay fever is therefore an allergic inflammatory disorder rather than an infection, and treatment aims to control the immune response and reduce exposure rather than eradicate a contagious organism.
