They're also sometimes used to prevent motion sickness and as a short-term treatment for sleeping difficulties (insomnia).
They're usually divided into two main groups: They also come in several different forms – including tablets, capsules, liquids, syrups, creams, lotions, gels, eye drops and nasal sprays.
Here, the histamines induce an inflammatory response — they dilate the blood vessels, increasing blood flow to the site of injury or invasion.
They also make blood vessels more permeable, allowing proteins and white blood cells to seep into the damaged or infected tissue.
Bender, Ph D, of National Jewish Medical and Research Center in Denver.
"The first-generation antihistamines are more sedating, but the distinction isn't as black-and-white as the marketing of the newer products may lead you to believe.