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Weed pollen allergy

Pollen from weeds can trigger hayfever, a type of allergy – your doctor may call it seasonal allergic rhinitis.

Hayfever occurs when your body makes the mistake of treating the weed pollen as a harmful organism, and the immune system goes into action by making antibodies to try to prevent it spreading. Symptoms of hayfever include sneezing, itchy, even watery eyes and a stuffy nose.

When do weed pollens trigger allergy symptoms?

Weed pollen allergy is seasonal, with weed pollen season mostly occurring between late June and September, although weed pollens can be released at any time between early spring to late autumn.

Pollen counts – the amount of pollen in the air – can vary. Symptoms normally appear when the count is above 50. Weather and biological factors can have an effect, so the pollen counts – and your symptoms – can be worse in some years than others. Pollen counts are often higher on warmer dry days than cooler wet days as rain removes pollen from the air, and they won't be the same in every region, so where you live in the country can determine your allergy symptoms. You may also have symptoms to only one type of weed pollen or to several, so when you experience symptoms will depend on which weed pollen you are allergic to and when it is released.

According to the Met Office, on average, the following weeds release pollen during these months:

  • Dock (Rumex) – pollen released between late May and early August, peaking between late June and late July
  • Mugwort (Artemisia) – pollen released between late June and early September, peaking between late July and mid-August
  • Nettle (Urtica) – pollen released between early May and late September, peaking between late June and early August
  • Oilseed rape (Brassica napus) – pollen released between late March and late July, peaking between early May and late June
  • Plaintain (Plantago) – pollen released between early May and late August, peaking between early June and mid-July.

Can weed pollen allergy be made worse by what I eat?

Some people with a weed pollen allergy may have a cross-reaction when they eat certain foods at the same time that weed pollen is in season. This is known as oral allergy syndrome or pollen food syndrome, and occurs when they eat certain fruits, vegetables or seeds, especially in raw form. It occurs because the proteins in the pollen are very similar to those in the foods.

In people with weed pollen allergy to mugwort, the most common foods that can cause a cross-reaction are:

  • Melons
  • Green peppers
  • Carrots
  • Celery
  • Parsnip
  • Sunflower seeds.

Because the process of digesting the food inactivates the allergen, the symptoms are normally limited to the mouth and throat, involving mild itching, swelling both of the lips, tongue, mouth or throat. They normally begin within minutes of eating the food, but then calm down within 30 minutes to an hour. Cooking the food can inactivate the allergen, which is why cooked foods are less likely to trigger symptoms.

Additionally, beer, wine and spirits contain histamine – the chemical responsible for allergy symptoms – so alcohol can make hayfever symptoms worse.

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