Antihistamine

Antihistamines are drugs which treat allergic rhinitis and other allergies. 
Usually people take antihistamines as an over-the-counter drug , with few side effects. It is for relief from nasal congestion, sneezing, or hives. These symptoms may be caused by pollen, dust mites, or allergy to animals. 
Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and respiratory tract infections near the lungs. Consultation of a medical professional is recommended for those who intend to take antihistamines for longer-term use.
Although people use the word “antihistamine” to describe drugs for treating allergies, doctors and scientists use the term to describe a class of drug that opposes the activity of histamine receptors in the body. In this sense of the word, antihistamines are subclassified according to which histamine receptor they act upon.