“The Influence of Weather and Climate on Hay Fever: Symptoms and Causes Explained”

People with hay fever suffer from pollen (pollen) in the air. The symptoms are most common in the spring, especially in the months of May and June. In recent years, however, complaints have often occurred much earlier. What is the influence of the weather and climate on hay fever?

What is hay fever?

Let’s start at the beginning; what exactly is hay fever? Hay fever is an allergy to pollen, also called pollen, from grasses and trees. Hay fever can cause various complaints. Think of complaints such as itchy or watery eyes, sneezing or shortness of breath. The complaints all stem from inhaling pollen (better known as pollen). Pollen from grasses in particular often causes problems.
Not only grasses cause hay fever complaints, but also herbs and trees. Normally it is like this: the higher the concentration of pollen, the more complaints.

The moment at which complaints can arise depends on when the plants bloom and to which plant species you are sensitive. Most grasses don’t start blooming until May (some one or two months earlier), but trees generally bloom earlier. In recent years, some people have been suffering from hay fever at the end of December due to hazel or alder pollen. New plants are also blooming in the Netherlands, for which people can also develop complaints. About 1 in 5 people in the Netherlands suffer from hay fever (20%).

Influence of the weather

Wind direction
The pollen production of flowers mainly takes place on dry, sunny and warm days and then mostly in the morning. On wet days with dew, fog or rain, the amount of pollen is much lower. Wind can spread the pollen through the air. In a strong wind, the pollen can travel up to 100 kilometers. The supply direction of the air is therefore very important for people who suffer from hay fever.
Air that has traveled a long way over land usually contains more pollen than air from the sea. An easterly wind can bring in air from Central and Eastern Europe, increasing the pollen concentration. In addition, many trees grow in these areas that flower later than in our country. In addition, an eastern supply direction is often a dry supply direction. This allows a lot of pollen to rise from the ground. If the wind comes from the west or north, it has also traveled a long way overland further inland. With a northwesterly wind, the pollen concentrations are therefore greater in Limburg than, for example, in Zeewolde. The severity of hay fever complaints can therefore differ between coastal residents and people living further inland.

Effect of thunderstorms
As mentioned earlier, rain normally washes the atmosphere clean and the pollen disappears. But this is not the case with thunderstorms. The reverse can even occur with a peak in pollen concentration being observed. We now dive a little deeper into the meteorological theory. Updrafts (wind moving upwards) can carry pollen up into the atmosphere, where it is broken into smaller pieces by the electrical charge of the thunderstorm.
These smaller pollen are transported back to the earth’s surface by the ‘downdraft’ and ‘outflow’ (wind moves downwards). It is precisely these smaller particles that penetrate deep into the human airways more easily and cause more complaints in hay fever patients. This phenomenon is also known as thunderstorm asthma.

Influence of climate (change)

The climate and especially the current climate change affects hay fever in different ways.
Higher temperatures cause the flowering and growing season to start earlier, but also increase the pollen count. So people suffer sooner and also more. If we look at 2023, we saw the first hay fever complaints in early January due to a mild autumn and a mild December. This was because the hazel was already in bloom at that time. Because it was quite wet and cold in the following months, the hay fever complaints remained limited.
Nevertheless, in the longer term it is expected that the growing season (and therefore the hay fever season) will be extended by about 40 days. New plants and trees that bloom later and can cause allergies, such as the olive tree, thrive in a warmer climate and are increasingly being planted in the Netherlands. An increased CO2 (and ozone) concentration causes an increase in the amount of pollen that plants can produce. In addition, the amount of allergens per pollen grain also increases.
It is therefore expected that hay fever complaints will increase in the future in the Netherlands due to climate change.