Standard hay fever calendar – high pollen times
Here is the standard hay fever calendar in the UK:
• The pollen season starts in February or March with pollens from trees becoming airborne.
• This is followed, from late May to mid-August, by the pollen from grasses.
• Most weeds pollinate between August and October. It is the low-growing weeds that tend to produce airborne pollen.
• Meanwhile mould, after lying dormant during winter, begins to release its spores into the air in the spring, reaching a peak in July and August and often continuing until the first frost.
Of course, not everyone with hay fever is allergic to all types of pollen. You may be surprised to read, though, that as many as 95 per cent of sufferers are allergic to the pollen from grasses, whereas only 10 per cent are allergic to the pollen from trees. In the USA, approximately 75 per cent of sufferers are allergic to the pollen from ragweed – a plant belonging to the daisy family which produces massive amounts of pollen.
The length of the pollen season has extended in recent years, the pollen count first peaking as early as March. This extension is believed to be another sign of world climate change.
Sources of pollen
In the UK, the following pollens often trigger hay fever symptoms:
• January – alder and hazel
• February – alder, poplar and hazel
• March – elm, poplar, willow, silver birch and ash
• April – silver birch and poplar
• May – grass, horse chestnut, poplar, silver birch, linden and oak
• June – grass, poplar, linden and weeds
• July – grass and weeds
• August – grass and weeds
• September – weeds and fungal spores
• October – fungal spores
• November – fungal spores.
Some people would include oilseed rape for May. However, it is usually the strong-smelling chemicals released by this plant that causes irritation of the upper respiratory tract. The grasses that mostly trigger an allergic reaction include sweet vernal grass, cocksfoot, meadow fescue, common reed, meadow grass, redtop and Johnson grass. The weeds that may provoke hay fever symptoms include nettles and dock.
In the course of a day
As the pollen season gets under way, pollen is released from plants early in the morning. If the day is sunny, more flowers open as the day grows warmer, with their pollen soaring high into the air. The pollen count rises in the early evening, when the air cools and the pollen falls closer to the ground. If the day is windy or humid, pollen tends to travel a greater distance and so pose a problem to more people. On rainy days, pollen is likely to be washed from the air, causing the pollen count to drop.