You need them to ease allergy symptoms such as a runny nose, sneezing, and itchy, watery eyes. They block a substance called histamine, which your immune system makes when you come across an allergen. You can get them over the counter and by prescription. Newer ones like cetirizine, desloratadine, fexofenadine, levocetirizine, and loratadine are less likely to make you sleepy. Check with your doctor or pharmacist.