1. Reduced sneezing, itchy eyes, and runny nose. Histamine causes the blood vessels in the nose and eyes to dilate and leak fluid, leading to nasal congestion, watery eyes, and sneezing. Antihistamines block this effect, preventing these symptoms from occurring.
2. Lessened itching and hives. Histamine also causes the release of chemicals that irritate nerve endings in the skin, leading to itching and hives. Antihistamines block this effect, preventing these symptoms from occurring or reducing their severity.
3. Decreased swelling. Histamine can also cause swelling in the nose, throat, and other parts of the body. Antihistamines block this effect, preventing or reducing swelling.
4. Lessened stomach upset. Some antihistamines can also block the effects of histamine on the stomach, which can reduce stomach upset and nausea.
Antihistamines are commonly used to treat allergic rhinitis (hay fever), urticaria (hives), and other allergic reactions. They are also sometimes used to prevent or treat motion sickness.
_Some side effects of antihistamines include dry mouth, drowsiness, fatigue, blurred vision, and nausea._