what are antihistamines used for

Antihistamines are a class of drugs used to treat symptoms of allergies caused by too much histamine, a chemical created by the bodys immune system. They are most commonly used to relieve symptoms of allergies such as hay fever, hives, conjunctivitis, and reactions to insect bites or stings. Antihistamines work by blocking the effects of histamine on certain cell receptors, which helps decrease allergy symptoms such as congestion, runny nose, sneezing, itching, swelling of the nasal passages, hives, and other skin rashes. They come in several different forms, including tablets, capsules, liquids, syrups, creams, lotions, gels, eyedrops, and nasal sprays. Antihistamines are divided into two major subtypes: H-1 receptor antagonists or H-1 blockers, which are used to treat allergy symptoms, and H-2 receptor antagonists or H-2 blockers, which are used to treat gastrointestinal conditions such as acid reflux, peptic ulcers, gastritis, motion sickness, nausea, and vomiting. The first-generation antihistamines were the first type approved by the FDA and are still prescribed today. They work on histamine receptors in the brain and spinal cord along with other types of receptors. Most notable about this generation of antihistamines is that they cross the blood-brain barrier, which can cause drowsiness and other side effects. The newer second-generation and third-generation antihistamines were developed to target their action on more specific receptors, which helps decrease side effects, including drowsiness. Also, these drugs work longer in the body, so you need fewer doses.