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Pollen Count

Pollen Count

A pollen count is generated by measuring the number of pollen grains in a given volume of air, using a pollen trap. In pollen counts, all pollen is treated the same. A count of 50 pollen grains or less is considered low, and a count of 1,000 pollen grains or more is considered high. The risk to you will depend on which plant pollens you are allergic to. Pollen count can significantly help to manage asthma and hay fever.

Frequently Asked Questions

A pollen forecast is based upon current pollen counts and information on the weather and time of year. The start of the pollen season can now be predicted quite accurately. These forecasts can be your guide to when to start taking antihistamines or extra asthma treatments.

Pollen counts tend to be higher in early morning and late evening, although they can sometimes be high all day long. If the grass is damp, the pollen peak will be later in the morning because the water evaporates before the pollen is released. Some grasses release their pollen in the afternoon. Pollen rises in the air during the day and then descends at night, as the air cools. In rural areas, the evening peak tends to occur between 6pm and 9pm but in the city, where the air stays warmer for longer, the pollen descends later and levels tend to peak between 9pm and midnight or even later, which is why you may wake up sneezing in the night. Sunny days favour higher pollen counts and rain tends to wash the pollen away. On a cloudy day, pollen builds up only to be released on the next sunny day.

The pollen season is the same for the hay fever season. The pollen season is different for different plants but it usually lasts from early Spring to late Autumn. A harsh winter will delay the start of the pollen season. Here is what to expect:

First out is tree pollen from mid to late March to mid-May. The season for each tree species lasts three to four weeks. These trees (listed from early to late with respect to their season) are associated with pollen allergy:

  • Hazel
  • Alder
  • Poplar
  • Ash
  • Birch
  • Oak

Next is the grass pollen season, which begins in mid-May and ends in July. The most common pollens associated with allergy in the UK are:

  • Foxtail
  • Oat
  • Dogstail
  • Timothy
  • Meadow grasses

Finally, the weed pollen season overlaps and extends beyond the grass pollen season – from the end of June to September. The exact duration depends upon the species of weed.

  • Dock weed has the longest pollen season, beginning in early Summer and finishing in mid-Autumn
  • Ragweed season runs from August to November
  • Nettle
  • Sorrel

Each plant produces as many as a billion pollen grains per season. It is a very powerful allergen with only minimal exposure often producing an attack.

The amount of pollen released by trees, grasses, and weeds depends upon temperature and amount of sunlight, so will vary from season to season. Allergic attacks tend to happen in the city a day or so after pollen is released from its source in the countryside. Even though pollen travels, levels are still usually higher in rural areas than in the city.

Grass pollen allergy is more common than tree or weed pollen allergy. Grass pollen grains are relatively large and tend to affect the nose and eyes more than the lungs. Wind-pollinated plants with small flowers are the main cause of pollen allergy. The wind carries the tiny grains of pollen on air currents and pollen may be found at a great distance from its plant source. Insect-pollinated plants, which tend to have bright flowers, are less likely to cause problems, but always heed pollen warnings on cut flowers like lilies. Check the following list for plants whose pollen could be causing you an allergy problem:

  • Trees: Ash, Birch, Cedar, Chestnut, Cypress, Elder, Elm, Hazel, Oak, Poplar, Sycamore, Walnut and Willow. 
  • Grass: Dogstal, Fescue, Foxtail, Meadow, Oat, Rye, Timothy and Vernal. 
  • Weeds: Dock, Mugwort, Nettle, Plantain, Ragweed, Sorrel, Wall and Pellitory.

At different times of year it is believed that certain foods consumed can react with pollens in the air - making your allergy symptoms worse. The foods that can react with pollens are as follows:

Pollen from Birch can react with: Celery, curry spices, raw tomato, raw carrot, apples, pears and kiwi. Pollen from grasses can react with: Oats, rye, wheat, kiwi and raw tomato. Pollen from weed can react with: Raw carrots and curry spices. Mould can react with: Yeast

Pollen grains may rupture in the high humidity before a storm breaks releasing lots of tiny starch granules. These are inhaled, often attached to diesel exhaust particles in urban areas, and may trigger an asthma attack at around the time when the thunder starts to rumble. Thunderstorm asthma tends to occur in people who have hay fever but do not usually suffer from asthma.