Climate change will provide longer pollen seasons and higher pollen concentrations and, as a result, the number of people suffering from allergies will increase. Pollen consists of tiny “seeds” or, rather, “ova” contained in flowers and plants and dispersed into the environment and air by the action of wind, insects and even birds, an allergen, therefore, that affects and weakens the health of many people.

The amount of pollen that is dispersed into the air depends both on the type of flore/plant and on the season and geographical location of the plant and, generally, the highest concentration of pollen is obtained during summer. Due to climate change, meteorology and its precipitation patterns are changing significantly: in the near future there will be more hot days than cold days and, in general, the seasons will be warmer and the concentration of carbon dioxide (CO₂) in the air will be higher than at present.

There are several allergic reactions caused by exposure to pollen that affect humans: hay fever (also more commonly known as “allergic rhinitis”), for example, perhaps is the most common. When allergens, such as pollen, enter the human body through the airways (nose and mouth), the immune system identifies them as threats so, with allergic rhinitis, the human body counteracts the allergen by producing and releasing particular chemicals that cause unpleasant and annoying symptoms in the nose (runny nose, congestion and constant sneezing). Depending on the type of allergen released into the air by the flower or plant, allergic rhinitis symptoms can occur all year round, threfore not just in summer, affecting hundreds of millions of people.

Another very annoying symptom caused by exposure to pollen is “allergic conjunctivitis”, an inflammation of the eye lining that causes redness, severe itching and excessive tear production. Conjunctivitis normally affects about 70% of people who already suffer from allergic rhinitis, while more generally, conjunctivitis can affect 30% of the world’s population even if they have never suffered from rhinitis. Furthermore, as far as respiratory diseases are concerned, people who already suffer from “asthma” are the most and sensitive and exposed to the discomfort caused by allergens, such as pollen: most of the strongest asthma attacks, in fact, are caused by pollen, especially in the warmer seasons.

Weather conditions can alter the quantity and seasonality of aeroallergens. The early blossoming of certain flowers and plants such as oak trees, for example, encourages increased production of pollen and carbon dioxide; therefore the rising temperatures and extreme rainfall should not be underestimated, both of which contribute to mould growth and worsening air quality: under these circumstances, the already precarious respiratory condition of people with asthma can only worsen and become more acute.