Common weed pollens and the importance of accurately identifying, treating and allergy

Allergy to specific pollens can make this period of the year particularly challenging for many people. Hay fever is widely recognised and commonly presents with symptoms such as sneezing, clear nasal discharge (rhinorrhoea) and itching of the eyes, nose and soft palate. Although these symptoms are often associated with grass or tree pollen, certain weed pollens may also trigger allergic reactions.  

People who are allergic to weed pollen may experience symptoms such as sneezing, itchy eyes/throat, cough and nasal congestion/rhinorrhoea during this season. The weed pollen season overlaps with the grass pollen season (late April to beginning of August) and can exacerbate these symptoms, as both types of pollen can be present simultaneously. 

 Weed pollen season in the UK typically lasts from late June to early September, with peak levels often occurring in July and August.  

Pollen from weeds such as Mugwort, Ragweed, Plantain and Nettle can be especially unpleasant allergens. There are no licensed immunotherapy treatments for these, to change the immunological response, so patients are left with basic management of antihistamines (which should be long acting and non-sedating), nasal steroid spray (or a combination of steroid/antihistamine spray), nasal saline douching and avoiding the pollens wherever possible.  

Distribution by wind action

Weather conditions play a significant role in pollen levels. Warm, dry and windy days can lead to higher pollen counts, while rain can help to wash pollen out of the air, temporarily reducing levels.  

Ragweed is an invasive annual weed which is not native to the UK and so relatively uncommon in some areas. It’s mainly found in southern England and Wales and can grow in areas that have been disturbed by human activities, such as alongside train tracks/railways, riverbanks, construction sites, wasteland etc.  

Ragweed pollen is very light and can travel in the warm air for hundreds of miles. There is ragweed in Europe as it thrives in warm, dry climates, so even though there may be no local ragweed plants nearby, people who have this allergy may still develop symptoms, which will need to be treated.  

Dockweed is also found on wasteland while Mugwort can also be found on embankments and meadows. It produces large amounts of wind-borne pollen and people with this allergy can also develop a cross-reactivity reaction with some foods. This is called pollen food syndrome (PFS). The Allergy UK website has a factsheet 1 on this where you can learn more about it. Some main foods which ‘cross react’ are celery, carrot, pistachio and mango. There are other foods as well. It is important to seek advice or referral for patients reporting these types of symptoms as they can get an itchy mouth and throat which can make them very anxious and lead to lots of dietary adjustments. These may reduce quality of life, so a correct diagnosis is important.  

Advanced techniques of allergy testing such as component resolved diagnostics (CRD) is often used in specialist Allergy/Immunology services to determine if there is a primary allergy or a cross reactivity with a pollen, especially when investigating food allergy, as risks needs to be assessed. These types of tests should only be undertaken where there has been adequate training in interpreting the results and understanding the context to be able to communicate the risk to the patient and, in the case of a primary nut allergy, prescribe adrenaline for risk of anaphylaxis. In the case of pollen food syndrome and cross reactivity, adrenaline is rarely required. It is this complexity which can be dealt with in Allergy/immunology services or via their advice.