Hay fever and airborne allergens
Hay fever is a very common allergy caused by pollen, house dust mite, pet hair or skin.
Applies to England
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Topic: environmental exposures
Air-related exposure: airborne allergens
Part of: The Health Risks of Airborne Allergens
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Hay Fever and Airborne Allergens
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About hay fever
Allergic rhinitis, more commonly known as hay fever, is an allergy caused by pollen, house dust mite or pet hair and skin (1) with common symptoms including:
- sneezing
- coughing
- runny or blocked nose
- itchy eyes, mouth or throat (2)
Hay fever is very common, with cases having trebled in the last 20 years. It affects 10 to 15% of children and 26% of adults in the UK (1). Hay fever normally develops during childhood or as a teenager, but can be triggered at any age. You are more likely to suffer from hay fever if you also suffer from eczema or asthma (1).
Although it is sometimes regarded as a small problem, hay fever causes disruption to sleep, which impacts daytime concentration, and causes people to miss days of work or school (1). People who have hay fever are also at an increased risk of developing asthma, highlighting the importance of treating this condition. For people who are allergic to pollen, it’s also worth knowing that certain things can worsen the effects of pollen, such as alcohol. Pollen levels can also be higher after rainfall if it is followed by dry weather (3).
Factors that impact pollen concentration
Pollen is a fine powder made up of tiny particles released by plants and trees and spread by insects and the wind (5). It can be inhaled by people and animals, and causes irritation and inflammation for those who are allergic to it (5). Birch pollen is the most dominant tree pollen in Northern and Central Europe and is a major cause of hay fever and, possibly, asthma symptoms (6).
Within the pollen season, different types of allergens peak at different times:
- tree pollens occur first from March until mid-May
- grass pollen then occurs from mid-May until July (this is the most common hay fever trigger)
- weed pollen can be released at any time but most typically the season occurs from the end of June until September (7)
Pollen seasons can be affected by many different factors, including where you are in the UK. For example, the pollen season is shorter and starts later in the North of the UK, and urban and coastal areas have lower counts than rural areas and inland locations.
Low winter temperatures can delay the season start because trees and plants that produce pollen remain dormant for longer. If there is not a lot of rain during spring then this can also reduce the amount of pollen produced. Rainfall generally causes a decrease in pollen concentrations, however, if rainfall is early in the day as well as heavy and prolonged, then it can keep pollen counts low all day (7).
A temperature between 18 to 28°C could mean a high count of grass pollen, whereas tree pollen will be highest between 12 to 15°C. Temperatures above 28°C reduces all pollen levels. Light winds mean pollen can struggle to get off the ground in order to travel, and if it’s extremely windy the pollen disperses far and wide, meaning its concentration thins out. Plants need sunlight in order to photosynthesise, which means that if there is a particularly cloudy day this is limited and plants produce less pollen (7).
What you should know about pollen
The ‘pollen count’ is a measure of how much pollen is present per cubic metre over 24 hours, so is used along with the weather forecast to predict pollen levels (8). Pollen counts tend to be lower in urban areas compared to the countryside, however, pollen can combine with air pollution in urban areas and worsen hay fever symptoms (3).
Hay fever also affects animals, and people should watch out for signs that their pets might be allergic to pollen (9).
References
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Allergy UK, ‘Allergic Rhinitis and Hay Fever’, 2021 (Viewed 25 March 2025)
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NHS, ‘Hay fever’ (Viewed 7 March 2025)
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Met Office, ‘10 things you should know about pollen’ (Viewed 20 March 2025)
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Cleveland Clinic, Allergic Rhinitis (Hay Fever): Symptoms & Treatment (Viewed 7 May 2025)
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Met Office, ‘Pollen Allergies’ (Viewed 20 March 2025)
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Biedermann T, Winther L, Till SJ, Panzner P, Knulst A, Valovirta E, ‘Birch pollen allergy in Europe’ European Journal of Allergy and Clinical Immunology: 2019 Volume 74(7) pages 1237-1248 (Viewed 20 March 2025)
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Met Office, ‘When is hay fever season in the UK?’ (Viewed 7 March 2025)
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Met Office, ‘Hay fever’ (Viewed 7 March 2025)
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Met Office, ‘How hay fever affects your pets’ (Viewed 7 March 2025)