Hay fever, also called allergic rhinitis, is an immune system reaction to pollen from trees, grasses, and weeds. These pollens are normally harmless, but in people with hay fever, the immune system mistakenly perceives them as a threat. When pollen is inhaled, the body produces immunoglobulin E (IgE) and the immune system activates mast cells, leading to inflammation and the typical symptoms of sneezing, itching, and a runny nose. The main triggers are pollen from trees such as birch, alder, and hazel, grass pollen, which is common in spring and summer, and weed pollen such as ragweed. Weather conditions also play a role; on windy days, pollen spreads further, increasing exposure. Mold spores and other airborne allergens can also contribute to symptoms. These allergens irritate the mucous membranes of the nose, eyes, and throat,...