@cavstat- Good morning and welcome to Mayo Clinic Connect. This is a great question. I'm not a doctor so I can't get into the chemistry of an antihistamine. I take Claritin and I'm hoping that since it reduces symptoms that irritate my sinuses and lungs it will help strengthen my immune system. Allergy symptoms happen when your immune system reacts to something harmless, like pollen, pet dander, or mold. Your body sees the allergen as an invader and attacks it, giving you a runny nose and itchy eyes. Allergy medicines counteract your body's reaction to your allergies. My impression is that If you have symptoms that continually batter you your body might have a harder time fighting off something else. Does this make sense? Have you spoken with your allergist about this?