When I was a child and was first diagnosed with hay fever, the doctor told me I would grow out of it. I didn’t ask for a rough date when that might be – I just went away and each year I suffered I hoped it would be the last. When I reached 20, it was still as bad as ever, as it was in my 30s and 40s. It’s mid-May and the grass pollen season is poised ready to start. I won’t be holding my breath.
As a pollen forecaster, I frequently meet hay fever sufferers who tell me they have “grown into it”. Hay fever can come along at any age although it mostly affects people who have a genetic predisposition towards it.
It can also affect people in different ways. For example, I’m affected by the earlier-flowering grasses and my symptoms tend to subside by late June, whereas a previous colleague didn’t get symptoms until late June. My younger sister is mildly affected whereas I get it quite badly. Some people are only affected at very high counts, others sneeze at just a few grains.
Hayfever is caused by pollen entering the nose and triggering a reaction in the mast cells causing them to release high amounts of histamine in an attempt to repel the invaders. The histamine release causes a raft of symptoms, including excessive sneezing, a runny nose, blocked sinuses, itchy palate, irritability and watery, itchy and inflamed eyes.
Not all pollen types cause an allergy. The worst offenders are a suite of tree pollens (hazel, alder, birch, plane and oak), grass pollen and a few weed pollens (nettle, dock, mugwort and plantain). All of these are pollinated by the wind and therefore become airborne in high amounts as they are dispersed between plants.
Grass pollen is the worst, affecting around 95% of hay fever sufferers. A pollen count of just 50 grass grains per cubic metre of air is sufficient is sufficient to trigger symptoms in all patients.
Flowers are often blamed for hay fever but these are largely insect-pollinated and the heavy, sticky pollen is unlikely to be breathed in.
The grass pollen season can start in April with several early-flowering types. This year, the grass pollen season is off to a late start due to the cold weather up to mid-April, but it will catch up and already a few grass species are in flower. The lawn grass (Poa annua) is flowering widely and abundantly this year, suggesting that the main season types will also. The main grass pollen season starts in late May and the first high count usually occurs in early June. So, what will this year’s season bring us?
Since the mid-nineties, pollen levels have been on the increase. Even in the predominantly cool, wet summers of the last six years, the total grass pollen catch has been average rather than low. We can assume this trend will continue this year and that, if the weather is good in June, we will have a severe season or at least an average one if it’s not.
There have been peaks and troughs in grass pollen since records began 60 years ago. Largely, the trends have followed the amount of grassland area. However, looking at the records for grassland cover reveals little change since the mid-nineties, suggesting that other factors have become more important.
So, what could these be? It is already well-established that climate change is affecting many plants in various ways. In the case of grasses it seems that warmer, wetter spring weather favours growth and allows them to produce more pollen. In addition, a number of researchers have examined the effects of higher CO2 levels on pollen production and found increases in some circumstances.
Researchers at the National Pollen and Aerobiology Research Unit, along with associates in Europe, have been looking at the amount of allergen that gets airborne. Pollen grains contain proteins and it is these that are the allergens that trigger symptoms. The research shows that sometimes the allergen amounts can be much higher than the actual pollen count. Further work will be conducted to determine why this occurs and whether or not the pollen grains are producing more proteins per grain – in other words, whether they are becoming more allergenic.