Antihistamine Different medications can treat allergies, including steroids and allergy shots, but usually the first thing to try is an antihistamine. When your body comes into contact with whatever your allergy trigger is -- pollen, ragweed, pet dander, or dust mites, for example it makes chemicals called histamines. They cause the tissue in your nose to swell (making it stuffy), your nose and eyes to run, and your eyes, nose, and sometimes mouth to itch. Sometimes you may also get an itchy rash on your skin, called hives.
Antihistamines reduce or block histamines, so they stop allergy symptoms.
These medicines work well to relieve symptoms of different types of allergies, including seasonal (hay fever), indoor, and food allergies. But they can't relieve every symptom. To treat nasal congestion, your doctor may recommend a decongestant. Some medicines combine an antihistamine and decongestant.