If you have started sneezing, sniffling, or feeling congested every fall despite never having allergies before, you are not imagining things. Many adults are surprised to learn that seasonal allergies can appear later in life, sometimes decades after childhood. Your immune system is not static. It can change how it responds to environmental triggers due to shifts in hormones, prior illnesses, where you live, or repeated exposure over time. Fall allergies can also be tricky ...