Cetirizine belongs to the class of medicines known as antihistamines. Cetirizine is a second-generation, anti-allergic, and non-sedating drug. 

Histamine is a useful substance; however, in any allergic reaction, it causes uncomfortable signs and symptoms such as watery eyes, itching, runny nose, blocked nose, redness on skin, sneezing, or skin rashes. On the other hand, antihistamines like Cetirizine block the histamine release and effects to lessen these symptoms