Environmental allergies, also known as allergic rhinitis or hay fever, occur when the immune system overreacts to harmless substances like pollen, dust mites, mold, or pet dander. Symptoms include sneezing, runny or congested nose, itchy eyes, throat irritation, and postnasal drip. Seasonal allergies (caused by pollen) and perennial allergies (year-round allergens like dust mites) can significantly affect quality of life.