Antihistamines are active ingredients that produce anti-allergic effects. These active ingredients cancel out or weaken the effect of the body's own messenger substance histamine. Antihistamines are used, among other things, for allergies, sleep problems, nausea, vomiting and colds.
If an allergy sufferer is confronted with allergens through the air (e.g. pollen), the skin (e.g. insect bites) or the gastrointestinal tract (e.g. food), the body releases the messenger substance histamine, which causes the allergic reaction.
Active ingredients such as azelastine or levocabastine in eye drops or nasal sprays and loratadine or cetirizine in tablets prevent histamine from docking with the specific histamine receptors.
These are called antihistamines because they compete with histamine for the histamine receptor binding sites. When the released histamine reaches the receptors, they are occupied and can no longer be activated by the histamine responsible for the allergy symptoms such as redness, swelling, itching, sneezing and runny nose.