Less sedating antihistamine
When you get injured or your immune system detects a potentially dangerous foreign substance, certain white blood cells and tissue cells release histamines that seek out and attach to other cells that have a histamine receptor.
Here, the histamines induce an inflammatory response — they dilate the blood vessels, increasing blood flow to the site of injury or invasion.
They can cross the blood-brain barrier and inhibit one of the other functions of histamines — that is, the pivotal role they play in regulating sleep and wakefulness.
Additionally, the increased fluid leakage from your blood vessels, combined with an increased mucous production — also caused by histamines — can result in a runny nose.Newer antihistamines such as loratadine (Claritin) and fexofenadine (Allegra) have been shown in clinical trials to cause less drowsiness than first-generation antihistamines.Allergies occur when your immune system erroneously thinks an innocuous foreign substance, such as pollen or pet dander, is actually dangerous.Histamines jump to action, causing the range of symptoms associated with allergies (sneezing, itchy eyes, chest congestion, wheezing, etc.).
They also make blood vessels more permeable, allowing proteins and white blood cells to seep into the damaged or infected tissue.
But there are side effects to this healing process.