What is the most common allergic thing?

The most common allergen worldwide is grass pollen. Grass pollen allergies affect up to 25% of the population in some areas and can cause a range of symptoms including sneezing, runny nose, itchy eyes, and nasal congestion. Grass pollen is released into the air by grasses during the spring and summer months, and can be particularly problematic for people who spend a lot of time outdoors.